Science, Politics & Religion Articles by B.J. Anderson
Et Tunc Nulla Erat IX (Dinos 2)
Et tunc nulla erat IX
(And Once There
Dinos: Part 2 of
Theropods’ temporal range is from
231.4-0.0 mya first appearing in the Late Triassic all the way to the present
as birds. The term ‘theropod’ means “beast footed” but the term ‘bird footed’
would have been more befitting since the pes (foot) are more comparable and the
theropodal end result is birds. This dinosaur group is mainly characterized in
having three-toed limbs, hollow bones and derived from a carnivorous ancestry.
Most theropods were carnivorous with recurved sharp teeth, but some evolved
into herbivores, scavengers, insectivores and primary piscivores.
Theropods are a very extensive and
diverse bipedal group of dinosaurs and in the innumerable cladistic structuring’
and phylogenetic rearranging. It can become confusing, as in the very
simplified clade list of divisions and subdivisions below. So, as revisions
continue to grow due to more fossil finds of new theropods, we’ll be presenting
clades in a much more facilitating manner.
In the Middle Triassic, theropods
evolved from lagosuchian ornithodirans. If you might recall, lagosuchians were
small lightly built archosaurs notable for slender legs and well developed feet
which was a prelude for primitive theropod features. The hind limbs were larger
than the forelimbs, but as facultative quadrupeds, could move bipedally with induced
Theropodal archosaurian ancestries were
ectotherms (cold blooded), but as active hunting terrestrial predators, (opposed
to lying in wait ambush semi aquatic predators as in extant crocodilians),
paleontological evidence and crocodilian oxidative metabolism points to the
fact that these early terrestrial archosaurs had the potential for improving
body heat. The theropod line and indeed dinosaurians in general took advantage
of this. For sure the avian bird-line theropods had developed endothermic
metabolism. Unlike mammalian endothermic down to the cellular in burning fuel
for generating heat, dinosaurs, like birds produced internal heat through
increased oxidative capacities. Other theropods were at least mesothermic (not
quite ectothermic but not quite endothermic either). This is evident from the
high muscular tissue content in theropods and other dinosaur lines. With
multiple strong and effective muscles, dinosaurs were active making them the
dominant animals during the Jurassic and Cretaceous.
The transformation from an ectothermic to
an endothermic metabolic state occurs by the interaction between the increased
basal uncoupling of aerobic metabolism from energy production demand. Increased
oxidative capacity and increased uncoupling of mitochondria witnessed in
developing bird embryos is a process controlled by tyrosine-based thyroid
hormones via its effect on PGC 1alpha (key regulator of energy metabolism) and
adenine nucleotide translocase (ANT) gene expression. Most likely, this was the
same molecular mechanisms for theropod endothermic capabilities.
Eoraptor skeletal anatomy
It appears that theropods originated in
what is now southern South America. Living 231-228 mya ago, Eoraptor (E-oh-rap-tor) was one of the
earliest lines of basal theropods and was found in Argentina’s ‘Ischigualasto
Formation’ composed of muddy siltstones. At 1m/3.3ft long, this animal was
slender and as lightly built running digitigrade (moving on its digits rather
than the whole foot) in an obligate bipedally upright position, it was designed
Credit: KN3 Eoraptor
Obligate or habitual bipedalism today is
a rarity as seen only in humans and kangaroos, but theropods were virtually all
bipeds. The only one I know of that could choose to walk as an occasional
quadruped was, Spinosaurus as long as
the pelvis could align and the manus wrist bones wouldn’t be crushed in the
overbearing weight. Eoraptor’s long
tubular bones, such as the femur were hollow.
Dentition was heterodont consisting of
serrated, recurved teeth in the upper jaw, as later theropods would possess and
leaf-shaped teeth in the lower jaw, like the teeth of basal sauropodomorphs. Eoraptor with its speed and agility
could easily overtake any of its small prey then immediately immobilize them
with its forelimbs’ formidable claws. But, due to its leaf-shaped herbivorous
teeth in the lower jaw, it is considered to be more as an omnivore.
Eoraptor was close in
relations to the 231.4-225 mya family, Herrerasauridae
(Huh-ree-ah-ruh-sawr-ruh-day) with multiple shared features such as the
saurischian lizard pelvis, but it is now phylogenetically been determined that
herrerasaurids were not ancestral to any later dinosaurian groups. It currently
is being proposed that Eoraptor may
be the common ancestor to all dinosaur groups with more emphasis towards the
sauropodomorpha line. Eoraptor went
extinct during the Triassic/Jurassic extinction.
Artist: Paul Sereno Eodromaeus
A basal theropod was Eodromaeus (E-o-dro-may-us). Occurring
231.4-229 mya during the Late Triassic of Argentina, Eodromaeus was relatively small at 1.2m/3.9ft in total length. The
main features to this primitive theropod were: it being a biped carnivore with
smaller forelimbs ending in hands that were transitioning from five to three
digits, as digits IV and V were shortening to the point of becoming vestigial.
Artist: Jorge Gonzalez Tawa
Theropodal cavity air sacs
occurred 215 mya during the Late Triassic and was one of the first N. America
early theropods to have lived in what is now New Mexico. At 2.5m/8.2ft long, it
had a very slender build as compared to other earlier theropods, but was a
trait to be characteristic of its descendants. The femur being longer than the
lower tibia and fibula leg bones was a unique feature, but the main
characteristic was that the neck vertebrae contained air sacs which were almost
identical to the air sacs of birds.
Artist: apsaravis Daemonosaurus
The name, Daemonosaurus (Day-mow-no-sawr-us) literally termed means,
‘prominent tooth’, but loosely termed means ‘buck tooth’ and for good reason.
At 1.5m/5ft long, this theropod may have been small, but considering its bite,
you would not want to tangle with it. What makes this theropod unique among
theropods is that its short skull bore large and sharp conical maxillary and
premaxillary teeth that protruded out from the tip of the mouth. There was a
lack of fusion between the braincase bones, but the fossil remains were of an adult
as the neurocentral sutures of the vertebrae were fused. Perhaps with the teeth
projecting outwards as they did, it was necessary to have unsown suturing and
expandable skull bones to accept the biting force of this animal. With its
unique skull traits, Daemonosaurus
was an early theropod that went extinct during the Triassic/Jurassic extinction
period and left no genetic lineage.
Artist: Maurillo Oliveira Tachiraptor
occurring in the Early Jurassic 200 mya was not a raptor, as the name might
imply to readers. It preceded the raptor family, Dromaeosauridae (Drom-me-ah-o-sawr-ah day) by 74 million years and
is not directly related. However, it represents a very primitive basal member
to Neotheropoda, therefore, it is an
unequivocal stem group to averostrans, the ‘bird snout dinosaurs’, in which
we’ll dwell on a bit later.
At 1.5m/4.9ft long, Tachiraptor ’s fossil remains were found in Venezuela and it is
considered a ‘ghost linage’ to birds. This shows that theropods were radiating
out from their place of origin in southern South America. Early theropod
species also began appearing in N. America during the connection between the
two present continents of N. and S. America. Also, Pangea at the
Triassic/Jurassic border connected these two continents to Asia and Africa.
Once land bridges were cut off by continental plate tectonics further into the
Jurassic and Cretaceous, theropod species as isolated evolved into newer
Postulating the spread from the earliest
dinosaurs originating from what is now Argentina and later into what is now N.
America, aids greatly in the understanding of the geological evolutionary role
played on dinosaurs by confirming the equatorial zone of the supercontinent
Pangea’s influence over the development of early dinosaurs through ecological
and geographical isolation via natural selection.
Neotheropoda simple Cladogram
Neotheropoda: This is a
major clade that includes all the theropod groups that survived the
Triassic/Jurassic extinction, namely the ceratosaurs, noasaurids,
abelisauroids, and the coelophysoids. Neotheropods’ revealed traits were size
increases of ilium surface attachments and enlarged pelvic muscles, while
reducing pedal (foot) digits I and V making the foot tridactyl while walking on
three toes. Also, there was a further reduction in manus (hand) digits IV and V
making the digits either vestigial or obsolete in later forms. These distal
limb features would now be the prevailing trait of theropods.
Coelophysoidea ~ (See-luh-phi-soy-dee-uh)
is an older sister group to averostrans and were small slender dinosaurs that
had radiated out globally.Coelophysoids
appeared 220-183 mya during the Late Triassic and Early Jurassic. Coelophysoids
were direct descendants of the earliest dinosaurs but with smaller slender
builds, dentition for capturing insects/small reptilian prey, definitive feathering
and hollow bones. As a predecessor, they passed these genetic traits onto coelurosaurs.
Artist: Alain Beneteau Procompsognathus
had a temporal range of 210 mya during the Late Triassic and was a small and
slender theropod at 1m/3.3ft long. It was a very refined and lightly built
dainty theropod as the name, taken from the Greek words, ‘kompsos’ and
‘gnathos’ attest to in meaning, ‘elegant jaw’ when put together respectively.
Long hind limbs, short forelimbs ending in large clawed hands, a long slender
snout filled with many tiny teeth and a stiffened tail are key features of Procompsognathus. This theropod dieted
on insects and small animals like lizards and the young of other smaller
dinosaurs. The fossil remains come from what is now Germany when the country
was a relatively dry and inland environment. The name Procompsognathus does not mean it is a direct descendent of Compsognathus. It only implies that with
some similarities, the former came long before the future one.
once considered a ceratosaur, then a basal coelophysoid and now is under dilophosaurids which are considered as a sister group to averostrans. It had two cranial crests that
sat atop the skull just below the neck and measured 7m/23ft long. The crests
were formed from extensions of the lacrimal and nasal bones and would’ve been
only useful as displays. There was no sexual dimorphism so both sexes supported
crests. With a temporal range of 193 mya in the Early Jurassic, its fossil
remains were discovered in Arizona, U.S. Dilophosaurus
had a weak bite and it was incapable of biting through bone as most theropods
easily could. It most likely, in conjunction with its manus distal claws used
its teeth to immobilize and kill smaller prey, then pick flesh off the bones.
Averostra simple Cladogram
(Ay-vee-ros-truh): With the term standing for ‘bird snouts’, averostrans were
composed primarily of two main groups and one subgroup in being the
ceratosaurians and tetanurans. The tetanuran line gave rise to the orionideans,
the largest of theropod groups. Through biomechanical studies, it’s been shown
that in the later and larger averostrans, the skull narrowed laterally but was
deep vertically. This shows averostrans were more dependent on strong repeated
bites in the skull withstanding the up and down pressures and forces from
repeatedly biting down hard into larger prey. But, in being narrower, the skull
was not equipped in resisting side to side pressures and forces due to
possessing a weak muscular and fragile jaw bone not capable to grip for the
shaking of prey.
(Seh-rat-o-sawr-ee-ah) ~ This is a clade of theropods that shared a common
ancestry to all the non-avian dinosaur groups, but possessed hollow bones as
did the maniraptoriforms, which includes birds. Diverging from the dinosaur
bird groups in the Early Jurassic, ceratosaurians arose 185 mya while dying out
66 mya at the end of the Late Cretaceous. An original ceratosaurian feature was
the complete fusion of the astragalus and calcaneum ankle bones. Known as the
tibiotarsus, this astragalus and calcaneum fusion to the tibia would survive
through the latter theropod line all the way to birds. Three main groups of
ceratosaurians were in the families: Ceratosauridae,
Noasauridae and the more derived Abelisauridae (Eh-bel-ah-sawr-ah-day).
Artist: karkemish00 Berberosaurus
A basal ceratosaurian was the 185 mya
Early Jurassic, Berberosaurus (Ber-ber-o-sawr-us)
and it may be the earliest of ceratosaurians. At 5m/16.4ft, its fossil site was
found in the continental series ‘Toundoute Group’ of Morocco. It was a biped
carnivore giving distinction to the later form theropod morphologies and
osteological anatomy in its vertebrae arrangement, metacarpals and hind
Artist: Yu Chen Limusaurus
Ceratosaurians were primitive predatory
theropods with the exception of the 161-157 million year old noasaurid, Limusaurus (Le-moo-sawr-us); it was an
herbivore in its adult stage. Isolated as the only known Asian ceratosaurian, Limusaurus through the process of aging
underwent a drastic transformational morphology. Juvenile teeth were lost and
replaced with a beak in the adult stage changing the diet as an omnivore to an
Artist: vaderxl Ceratosaurus
Two ceratosaurians were the
ceratosaurid, Ceratosaurus (in which Ceratosauria derives its name) and Genyodectes (Jin-yo-decks) where both supported head
crests, although it’s only purported that Genyodectes
had crests. In addition, Ceratosaurus
sported a nose horn with large nasal passages and small osteoderm armor running
down its spine. Similar to birds, the sacrum and pelvic bones were fused
together. Ceratosaurs at 5.3m/17.4ft long had radiated out into Utah/Colorado
U.S., Tanzania and Portugal. The temporal range during the Late Jurassic was
153-148 mya. It was ancestral to abelisaurids and Carnotaurus (Car-no-tar-us), which also possessed high crested brow
ridges. Carnotaurus also made T. rex look like it had Arnold Schwarzenegger
arms as this 8.25m/ 27.1ft long dinosaur’s vestigial forelimbs were tiny.
Artist: teratophoneus Genyodectes
In the superfamily Abelisauroidea (Eh-bel-ah-sawr-oi-dee-ah) are the two sister group
families of noasaurids and abeilosaurids. Noasaurids appeared from the Late
Jurassic until the Late Cretaceous 161-69 mya, while the temporal range of
abelisaurids was from the Middle Jurassic until the end of the Late Cretaceous
Artist: cisiopurple Abelosaurids
In the family, Abeilosauridae some unique characteristics were in the skull having
ornamentation of brow ridges/horns with grooves and pits, very short but tall
skulls due to the vertically lengthened premaxilla blunting the front of the
snout, hind limbs comparable to ceratosaur legs and vestigial forelimbs.
Abelisaurids formed a transitional intermediate relationship between Ceratosaurus and Carnotaurus and were closely related to both.
Artist: Wayne D. Barlow Xenotarsosaurus
The abelisaurid, Xenotarsosaurus (Zee-no-tar-so-sawr-us) at 5.4m/18ft long occurred
in the Late Cretaceous 95mya. Found in Argentina’s ‘Bajo Barreal Formation’, it
had the unique ceratosaurian feature in showing a complete fusion between the
astragalus and calcaneum ankle bones. With this complete fusion without any
visible suturing and further fusion of the astragalus/calcaneum element to the
widened distal end of the tibia, there is a prevailing thought to remove Xenotarsosaurus from the family, Abelisauridae and list it as a basal
neoceratopsian with uncertain affinities. However, due to its’ remains showing
numerous Carnotaurus features, as
skull traits, it is still listed as an abelisaurid.
Artist: Damir G. Martin Carnotaurus
One odd derived abelisaurid that
occurred in the Late Cretaceous 72-69.9 mya ago was Carnotaurus. At 9m/29.5ft it had a very muscular neck with the
deepened skull supporting thick bull-like horns just above the eyes. Also, the
forelimbs were vestigial while the hind limbs were long and slender adapted for
running. The horns, measuring 15cm/5.9in were formed from the frontal bones and
most likely were sheathed in keratin. With the neck musculature, thick skull
and horns, most likely the head was used as butting weapons against
conspecifics (members of the same species). The eye orbits were small, so the
eyes were better equipped to avoid injury during ramming bouts.
Artist: Philip Hood Noasaurus attacking Saltasaurus
Noasaurids are defined as all theropods
closer to the ceratosaurian noasaurid, Noasaurus
(No-ah-sawr-us) than to Carnotaurus.
Unique features of noasaurids are a low rectangular arrangement of the mid
caudal neural spines, a coracoid (a structure stationed anteriorly on the
scapula) that is almost double the width than its length, a stout humeral head
and the tibia possessing a flat anterior at the distal end.
Credit: Pixel Dust Studios M. knopfleri
(Phonetics: May-shuh-kuh-sawr-us = nop-fleur-eye) was a 1.9m/6.2ft noasaurid
that lived during the Late Cretaceous 70 mya. It had heterodont teeth along the
jawlines while the front teeth projected forwards. The species name, knopfleri was used due to the two
paleontologists always jamming out to the rock band, ‘Dire Straits’ while
working on the Madagascar fossil dig. Mark Knopfler was the band’s leader.
The name refers to ‘stiff tails’ and is a clade including megalosauroids
(temporal range: 170-93 mya), allosauroids (temporal range: 175.6-70 mya),
tyrannosauroids (temporal range: 165-66 mya) and maniraptoriforms (temporal
range: 167-0 mya) which includes maniraptors, ornithomimosaurs and birds.
Tetanurans are those dinosaurs more related to birds than to their
contemporaneous ceratosaurian cousins. In tetanuran evolution, there were
multiple parallel diversifications of multiple lineages. Tetanurans are
identified by two skull types. The first is more primitive being three times
longer than tall and ends in a blunter snout than the second. The first skull
also, along the lacrimal, nasal and frontal bones was ornamented with horns,
crests and spikes. In the second skull type, it’s also longer than tall, but
much lower and with less elaboration of ornamentation. Tetanurans and the
ceratosaurian line diverged and split during the Late Cretaceous more than 200
mya. But the biggest transition from primitive theropods to the most derived
occurs within the tetanuran clade.
From tetanurans onwards, as big and
diverse a clade as it was, only birds still exist just like modern humans are
the only hominid that still exists, but with a much shorter temporal range than
that of tetanurans. We’ve got a long way to go to match the success of
tetanurans who roamed Earth for 100 million years. The oldest known hominids
are Orrorin tugenensis and Sahelanthropus tchadensis in that both
lived ~ 6 mya.
Two basal tetanurans were the previously
discussed, Antarctic Elvis Presley crested, Cryolophosaurus
and its sister taxon, Sinosaurus (Sye-no-sawr-us)
that lived during the Early Jurassic 201-196 mya. As a medium sized dinosaur,
at 5.6m/18.4ft, Sinosaurus was
closely related to the North American Dilophosaurus,
so much so that it was, until recently, once considered to be an Asian
dilophosaurid. Just like the ceratosaur crest, the sinosaur crest was too
fragile for defense so likely was used for display purposes and/or species
Orionedes simple Cladogram
(O-rye-o-nye-dees): This is a major tetanuran theropod clade that had a
temporal range from the Middle Jurassic to the present 175.6-0.0 mya. The
tetanuran clade includes most of the theropod groups, including birds. Large tetanurans
are contained in the Orionides node,
such as allosaurids, spinosaurids and carcharodontosaurids that reached lengths
of 18m/59ft. The spinoraurid, Spinosaurus
aegyptiacus (Phonetics: Spy-no-sawr-us = e-gyp-tuh-cus) is the largest
terrestrial predator of all times.
Orionides is comprised of the two clades, Megalosauroidea (Meg-uh-lo-sawr-oi-dee-uh) and Avetheropoda (Ay-vee-the-rop-o-duh), along with these two clades’
most recent common ancestors and descendants.
Megalosauroideans temporal range was during the Middle Jurassic to the Late
Cretaceous 170-93 mya. This clade is the sister group to Avetheropoda. Just to note, the term, ‘Spinosauroidea’ is
synonymous to Megalosauroidea and is
sometimes used in place of. The three genera members of the family, Piatnitzkysauridae (Pee-ut-nits-kee-sawr-ah-day)
are basal megalosauroids composed of: Condorraptor
(Marsh-o-sawr-us) and Piatnitzkysaurus
(Pee-ut-nits-kee-sawr-us), in which gave the name to the family. This gives the
real definition of piantnitzkysaurids as those megalosauroids that are more
closely related to Piatnitzkysaurus
than to the other megalosauroids. Piatnitzkysaurid shared traits were in
having, among others, vertically ridged paradental plates, anteriorly inclined
posterior dorsal neural spines and a humerus with a canted (bent forward and
away from body) distal condyle (rounded knob of humerus bone). Piatnitzkysaurus
synapomorphies (distinguishing features) from the more derived megalosauroid
are: a small or absent anterior process of the maxilla, moderately developed
axis diapophyses (diapophysis ~ singular; transverse process of a vertebra) and
an absence of axial pleurocoels (hollow depressions on lateral portions of vertebrae).
Credit: De Agostini Picture Library Piatnitzkysaurus
The sister group to Piatnitzkysaurids
(Meg-uh-lo-sawr-e-uh) and it is composed of the basal megalosaurid, Streptospondylus (Strep-toe-spon-dill-us)
that occurred in the Late Jurassic 161 mya and the two major sister families of,
(Meg-uh-lo-sawr-uh-day) and Spinosauridae
(Spy-no-sawr-uh-day) that occurred respectively in the Late Jurassic 170-148
mya and in the Late Jurassic to the Late Cretaceous 148-93 mya.
Artist illustration: Sergey Krasovskiy Torvosaurus
One megalosaurid was, Torvosaurus (Tor-voe-sawr-us) that
existed in the Late Jurassic 153-148 mya and was the largest carnivore of the
Jurassic Period with a length of 10m/33ft. Its narrow snout, with a kinked
profile just above the large nostrils, had in its front most snout bone (premaxilla),
three flat teeth oriented outwards with the front edge of the teeth crown
overlapping the outer side of the rear edge of the preceding crown. Torvosaurus was an apex predator in Late
Jurassic N. America and Portugal and most likely scavenged other predator kills
and hunted either in packs or solitarily other larger dinosaur herbivores.
There are two species in T. tanneri (tan-nur-ree) of USA, Colorado
and T. gurneyi (grr-nee-ah) of Portugal. In the Late Jurassic N. America
and Europe were connected where Torvosaurus
evolved as one species. Once the continents split, it evolved through
isolation and natural selection as two separate species.
The oldest clutch of fossilized dinosaur
eggs was found in what is now western Portugal and were laid down by a Torvosaurus mother between 152-145 mya.
In addition to the eggs being shown to be single layered, the eggs also housed
fossilized embryonic stages.
Artist: David Bonadonna Spinosaurus aegypticus
Spinosaurids first appeared in the Late
Jurassic 148 mya and went extinct 93 mya in the Late Cretaceous. Spinosaurids
had elongated crocodile-like snouts with very little if any serrated teeth that
were conical in shape. The conical teeth were excellent for grabbing onto
slippery prey, such as fish, in which spinosaurids were the most aquatic of large
dinosaurs in being semiaquatic. Also, the largest carnivore ever was in the
spinosaurid, Spinosaurusaegypticus reaching a length of
18m/59ft. The major characteristic of spinosaurids was in the sail that the
dorsal vertebral spines of the back supported. In fact, the term, Spinosaurus refers to ‘spine lizard’.
These spines were nearly 2m/6.5ft tall. Along with the genus, Spinosaurus that occurred 112-92.5 mya,
there were four other spinosaurid genera in, Baryonyx (Bar-ee-on-iks) 130-125 mya, Siamosaurus (Sye-am-o-sawr-us) 130 mya, Suchimimus (Su-ko-mie-mus) 125-112 mya, Irritator (Ear-re-tay-tor) 110 mya and occurring ~ 119 mya was Ichtyovenator (Ick-thee-o-ven-a-tor) that
had two separate sails down its back. The sails of Ichtyovenator were separate with the first as the highest ending
abruptly with the second sail from the separation rising down towards the tail.
This is an indication that the sails of all spinosaurids were for display
purposes for mating recognition and/or for appearing larger.
Through oxygen isotope studies of
spinosaurid bones, as compared to other theropod fossils and extant
turtles/crocodiles, the spinosaurid isotopic ratios were much closer to living
turtles and crocodiles than to other theropod remains alluding to a semiaquatic
lifestyle.The main source of prey for
spinosaurids was fish, but they were also opportunistic and if aquatic prey
wasn’t available would hunt down terrestrial prey. Baryonyx and Spinosaurus
both ate fish, but where Baryonyx was
more of a carnivore than a piscivore, Spinosaurus
was more of a piscivore than a carnivore.
There are four other genera listed under
the family, Spinosauridae, but due to
scant fossil material are only suspect spinosaurids as they might be synonymous
to established spinosaurids or are simply nomen dubium.
Avetheropoda clade with Allosauroidea ousting Carnosauria
first occurred in the Late Jurassic 175.6 mya and still exist in the present as
extant birds. As the sister taxon to Megalosauroidea,
avetheropods refers to ‘bird footed dinosaurs’ and it is in a section of this
clade that contains the major path to birds with its most common ancestors and
all of its descendants. The famed Tyrannosaurus
is also an avetheropod, although it was not in the direct line to birds. The
simple relationship grouping below shows the avetheropod major groups.
The first sectioning of avetheropod
relations is in the two clades, Coelurosauria
(Phonetics: See-lure-o-sawr-ree-uh) and Allosauroidea
(Phonetics: Al-lo-sawr-oi-dee-uh). You will find at times Carnosauria in place of Allosauroidea.
I’m even using it in the tetanuran clade. That’s fine as both are still
acceptable, but as time moves on Allosauroidea
is going to be the permanent term.
Avetheropod shared characteristics are
in possessing extremely complex vertebrate air sac chambers and in the loss or
only a vestigial single metacarpal of the manus digit IV making the manus (hand),
like the pes (foot), functionally tridactyl.
Allosauroidea ~ occurred in
the Middle Jurassic 175.6 mya to the Late Cretaceous 70 mya. It appears that
there was a co-evolutionary race between herbivores and allosauroids, for as
when herbivores started increasing in size and inheriting newer weaponry in
spikes, clubs and bony plates, allosauroids began their increases in size,
speed and agility. The two main derived sister taxa (plural for taxon) of
allosauroids are Metriacanthosauridae
(Phonetics: Met-rih-ah-kanth-o-sawr-uh-day) and Allosauria (Phonetics: Al-lo-sawr-e-ah).
The primitive allosauroid members all
belong to the family, Metriacanthosauridae.
Currently comprising six genera, metriacanthosaurids ranged in size from
4.5m/15ft to 10.8m/35.4ft long. The synapomorphies shared with the more derived
allosauroids were: a fused distal end of the ischium, a manus shorter than the
forearm, the laterosphenoid (lateral form of cranium’s sphenoid bone that is
ossified cartilage) was articulated on the frontal and postorbital skull bones,
sub-rectangular and sheet-like neural spines of the middle caudal vertebrae while
the manus lacked digit V as well as the phalanges of digit IV.
Unique features of metriacanthosaurids
were: a pronounced ventral keel on the anterior dorsal vertebrae, a straight
posterior margin of the iliac post-acetabular process at the ventral inflection
point, a ventrally curved ischial shaft and a bulbous fibular crest on the
order consists of two sister taxa in the family of, Allosauridae and the order of, Carcharodontosauria
(Phonetics: Car-care-o-don-toe-sawr-e-uh). Occurring 155-146.8 mya during the
Late Jurassic, Allosauridae consists
of three genera in: Allosaurus, Epanterix and Saurophaganax (Sawr-o-fag-uh-nax). There are three species of Allosaurus in: A. fragilis, A. europaeus,
and A. lucasi with A. fragilis being the more famous. Epanterias lived 146.8 mya at the end of
the Late Jurassic and was large at 12m/40 ft. The largest allosaurid however,
was Saurophaganax at 13m/43ft in
length living 150 mya in the Late Jurassic.
Artist: atrox1 A. fragilis
Allosaurid anatomy was typical of large
tetanuran theropods, but all teeth were serrated with five teeth seated in the
premaxillary and sixteen in the maxilla. Also, digit I of the manus formed an
opposable thumb. All allosaur fossils come from N. America’s ‘Morrison
Formation’. It is mainly composed of shallow sea and alluvial sedimentary rock.
Allosaurid fossil remains are found in the basin portion of the formation
formed from the uplifting of the Rocky Mountains.
Artist: Manuel G. Jaramillo Saurophaganax
One other suspect allosaurid found in
the midsection of the Morrison Formation in what is now Oklahoma was, Saurophaganax. Being larger than the
other allosaurids, it is also much rarer in fossil finds. The scenario in lack
of fossils supports the idea that larger predators have smaller populations,
due to the fact that larger animals are restricted to population growths as not
to restrict food sources. However, as big as Saurophaganax was, it could easily steal a meal from a much smaller
predator’s kill. Saurophaganax is
Oklahoma’s state fossil.
Carcharodontosauria encompasses the
two families of, Neovenatoridae
(Nee-o-vuh-nay-tor-uh-day) and Carcharodontosauridae.
Neovenatorids had a temporal of 128-93 mya in the Early-Late Cretaceous. As
compared to other allosauroids, their shoulder blades were much wider and
shorter while the ilium was pocketed with cavities. Neovenatorids have had
fossil discoveries in China, northern Africa, S. America and N. America.
Neovenatorids consist of five genera plus the unranked file of, Megaraptora (Meg-uh-rap-tor-ah) that has
another five genera. One with coelurosaurian characteristics has just been
discovered in Australia, but with controversial relations to other allosauroids
as they also have basal coelurosaurian anatomical traits. With the discovery of
the as yet unnamed Australian fossil find dating back to 110 mya in the Early
Cretaceous, its age makes it the oldest and most primitive megaraptoran.
Therefore the evolution of megaraptorans originated in Australia and radiated
out during the Gondwanan connection if it is finalized as a true maegaraptoran.
Artist: Jorge Gonzalez Siats
Siats (See-atch) is a
neovenatorid with remains discovered in the ‘Cedar Mountain Formation’ of Utah,
U.S. from the Late Cretaceous 98.5 mya. The term, Siats comes from the Native American, Ute tribe meaning ‘man eating
monster’ in their mythology. Siats
autapomorphic unique traits were a subtriangular cross section of the distal
caudal vertebrae, broad neural spines on the dorsal vertebrae and a
transversely concaved acetabular rim of the iliac (relating to ilium) pubic
peduncle. As one of the largest known N. American theropods, it reached a
length of 11.9m/39ft and filled the large carnivore gap in N. America between
the earlier carcharodontosaurs and the latter tyrannosaurs.
Artist: Julio Lacerda Gualicho
Another neovenatorid was the Late
Cretaceous 90 mya, Gualicho
(Gwah-lee-cho). This 6.5m/21.3ft long neovenatorid had already possessed the
reduction of forelimbs ending in only two fingers. The arms were about the size
of a child toddler’s. This is an indication that allosaurians were evolving
reduced forelimbs just as tyrannosauroids were, but independent of each other.
Coming from what is now Argentina, Gualicho
lived at a time when Argentina was a part of northern Patagonia after having
split off from the supercontinent, Gondwana. Although Gualicho is a neovenatorid, it doesn’t fit nicely into any taxa
grouping and is considered ‘mosaic’. Its anatomy suggests two things: either both
megaraptorans and neovenatorids were carnosaurs, or that these two groups were
a grade of theropods more closely related to coelurosaurs than to carnosaurs.
Artist: Damir G. Martin Giganotosaurus
Carcharodontosauridae ranges from the
Late Jurassic to the Late Cretaceous 154-89 mya comprising nine genera, one
with one genus and within the subfamily one tribe (Giganotosaurini) with three genera. The defining term of Carcharodontosauridae is
caecharodontosaurians that are closer in relations to, Carcharodontosaurus than to Allosaurus.
Carcharodontosaurid features were foremost, no matter their size, a distinctly
oversized head in comparison to their body, in which their fossil skulls are
the largest of any dinosaur group. Acrocanthosaurus
(Ak-row-can-tho-sawr-us), living in the Early Cretaceous 116-110 mya and
measuring 11.5m/38ft in total length had a head measuring 1.3m/4.3ft. Giganotosaurus (Jig-uh-not-o-sawr-us)
lived 98-97 mya during the Late Cretaceous was 13m/43ft long and had a head ~
1.8m/5.9ft in total length. The skulls were not heavy though as they were
filled with large fenestrae that decreased weight. Like most of the larger and
later derived theropods, their forearms were much smaller than the hind limbs,
but the carcharodontosaurid forelimb was robust with strong muscles as muscular
attachments attest in the arms’ fossil bones.
Artist: Xing Lida Acrocanthosaurus
Acrocanthosaurus had a row of
tall neural spines at least 2.5 times that of the vertebra that ran the length
of the back from the neck to down to the upper tail. These spines may have
served as a fat reservoir and temperature control. There might only be a
hypothesis of thermoregulation in Acrocanthosaurus,
but in Giganotosaurus there is very
good evidence that it was at least homeothermic. The fossil bones’ oxygen
isotope patterns indicated an even heat distribution throughout the body which
would have created a stable core temperature giving a metabolism between that
of a mammal and a reptile. This in turn would have benefitted a rapid growth
rate and an increase in cursorial (running) speed. In calculating the kinetic
running speed limit in the time it would take for one of its sized legs to gain
balance after the retraction of the other leg, it was found that the speed Giganotosaurus could safely obtain was
14m/45.9ft per second or an astounding 50km/hr-31mph. In running, the heavily
stiffened tail acted as a counterbalance.
One other carcharodontosaurid was, Concavenator (Con-kah-veh-nay-tuhr) that
arose 130 mya in the Early Cretaceous. This medium sized 6m/20ft long theropod
had some interesting features. Fossil remains of Concavenator’s posterolateral surface of the ulna (forelimb)
possess homologous quill knobs, an anatomical trait found only in extant
animals with large quilled forelimb feathers. Fossil impressions also reveal
wide rectangular scales located underneath the tail and feet resembling extant
birds’ covering of scutes and plantar pads on their undersides. The main trait
though, is just in front and above the pelvis an extension of two elongated
presacral vertebrae and along with a series of shorter, but more elongated than
the rest of the neural spines, most likely supported a sail. The elongated
spine row originated just in front of the hips and terminated at the base of
the tail. From thermoregulation to fat storage, there is much speculation on
why this hip sail evolved, so I’m going to throw in another.
Artist: Frank Lode Concavenator
One thought of mine is in the body plan.
Vertebrates have bilateral symmetry creating only one sagittal plane; basically
creating a mirror image from both body halves when bisected. For a lying in
wait ambush predator, the sail could’ve acted in a way as camouflage,
distorting the potential prey’s viewpoint recognition of the predator’s general
body outline. This would’ve given Concavenator
an advantage of pouncing on and subduing prey at much closer range exerting
less energy in the encounter as opposed to a chase and encounter.
Just like Convenator and Acrocanthosaurus,
other orinidans, such as the spinosaurids, Metriacanthosaurus
and Becklespinax all had sails, so
they inherited it from a common ancestor ruling out convergent evolution.
Coelurosauria ~ had a
temporal range of 165-0.0 mya during the Late Jurassic to the present. This
subgroup of Orionides comprises the
compsognathids, tryrannosauroids, ornithomimosaurians and maniraptoriforms
which include birds. The generic term, ‘coelurosaurus’ is a blanket moniker
referring to the smaller coelurosaurians and does not represent any individual
species. Although most were small, coelurosaurian sizes ranged from Parvicursor (Par-vee-cur-sor) at
39cm/29.5in long to Tyrannosaurus
(Tie-ran-no-sawr-us) at 12.3m/40ft long with a potential of reaching
Virtually all of the smaller
coelurosaurians from the most primitive to the most derived possessed
feathering over parts or the entire body. Even some of the larger
coelurosaurian fossil remains show evidence of feathering. Although there is no
direct evidence that Tyarannosaurusrex possessed feathers, there is
indirect evidence that it did. Dilong
(Di-long), occurring 126 mya in the Early Cretaceous was a basal tyrannosauroid
in the direct line to T. rex and it had feathers. The feathering
was simple filaments and would’ve given the 2m/9.9ft long, Dilong a shaggy appearance.
Artist: Cheung Chun Tat Yutyrannus
The recently discovered fossil remains
of, Yutyrannus (U-ty-ran-nus) was
even a more evolved ancestral tyrannosauroid in direct relations to T.rex
and it had feathers all over its body. This 9m/29.5ft long tyrannosauroid lived
124.6 mya during the Early Cretaceous and is the largest known theropod with
direct evidence in donning feathers. Even the name, Yutyrannus means ‘feathered tyrant’. The feathers of these two
theropods would have served as insulation. While Dilong was cloaked in feathers and Yutyrannus was tucked in a tuft of plushy feathering, there are
some T. rex scale impressions from fossil remains, but as yet no feathers.
Distinguishable traits found in all
(vertebrae series attached to hips) longer than in other dinosaurs
stiffened towards the tip
ulna (lower arm bone)
(lower leg bone) that is longer than the femur (upper leg bone)
intramandibular joint inherited from primitive to derived forms
Basal coelurosaurians were smaller than
their allosauroid, megalosauroid and tyrannosauroid outgroups, but were also
larger than their ornithomimosaur, oviraptorosaur and alvarezsaurid outgroups.
So, coelurosaurs trended towards miniaturization as well as gigantism.
Artist: Michael B.H. Zuolong
occurring 161.2-155.2 mya in the Late Cretaceous ‘Shishugou Formation’ of China
is the most basal coelurosaurian found thus far. It was 3.1m/10ft long and
despite its coelurosaur primitiveness, it may turn out to be more derived than
There was some initial speculation that,
was a direct ancestor to all coelurosaurians. Living 90 mya in the Late
Cretaceous, Bicentenaria most
definitely is not the true ancestor to all coelurosaurs, as it is ~ 70 million
years too late for that since coelurosaurs were already an established
diverging group during the Late Jurassic 165 mya. But its fossil finds are
unique as it is a transitional form in possessing both primitive and derived
coelurosaurian anatomical traits.
Illustration Artist: Christian Masnaghetti Bicentnaria
This 2.5-3m/8-10ft coelurosaur possessed
primitive plesiomorphic traits such as having long slender tridactyl pes and
manus (feet and hands) that were fashioned for speed running and grasping,
while possessing ziphodont teeth, the laterally compressed, curved and serrated
dentition allowed for slashing, grasping and seizing. A few of the more derived
autapomorphies were in the humerus bearing a deep fossa on its surface, premaxillary
teeth with mesial denticles only at the base of the crown and a spoon-shaped retroarticular
process [ventral end of zygomatic arch (cheek bone)] was dorsoventrally
depressed and transversely wide.
The fossils, including subadult and
adult remains were found as washed up into a pile in the Late Cretaceous
Argentine sediment of the ‘Ezequiel Ramos Mexia Reservoir’ in Argentina’s
Patagonia region. The name, Bicentenaria
refers to Argentina’s bicentennial years as a nation. There had been
speculation that it was a social animal due to the pile up of fossil bones, but
once geological and taphonomic (taphonomy: the paleontology branch dealing with
the processes of fossilization) considerations were employed, the fossils were
individuals that had previously died in separate places when afterwards parts
of their remains were washed away and heap deposited during separate time
Artist: Tom Miller Huaxiagnathus
is a family of coelurosaurians that had a temporal range during the Late
Jurassic to Early Cretaceous 151.5-108 mya. Huaxiagnathus
(Wash-ag-nuh-thuse) and Sinocalliopteryx
(Sye-no-cal-ee-op-ter-ix) were by far the largest at 1.8m/5.9ft and 2.4m/7.8ft
long respectively, while most were just under or at 1m/3.3ft in total length.
In being the largest, these two compsognathids were also two of the earliest
compsognathids, showing that this group overall were trending towards miniaturization
as compsognathid species were some of the smallest dinosaurs found so far.
Artist: Cheung Chun Tat Sinocalliopteryx
In being small, compsognathids had the
generic smallish coelurosaurian characteristics of large eyes, a three-fingered
manus (hand) and an S-shaped neck and rigid long tail. Scales, filamentous
feathering and skin impressions have been found among their fossils. Even
though they had bird features their genetic line went extinct before the Late
The specific characteristic trait of
compsognathid anatomical features was the shared feature in the distal end of
the manus. As in all coelurosaurians, digit I is longer than all the other
metacarpal digits, but in compsognathid manus morphology, the metacarpal in
digit I is stockier and shorter than in other coelurosaurians. With
compsognathids, there is also a projection from digit I.
Compsognathid diets most likely
consisted of small vertebrates and large insects. They appear to have been
especially fond of small lizards as the remains of lizards have been found in
the digestive tracts of several compsognathid fossils.
At 1.1m/3.6ft, Sinosauropteryx (Sye-no-sawr-op-tear-icks) and not to be confused
with the aforementioned, Sinocalliopteryx,
was a compsognathid that roamed open Early Cretaceous habitats 124.6-122 mya.
Its fossil finds are very important due to the fact the remains still retained
the feathering pigmentation, giving us evidence of its coloration. The pigments
of Sinosauropteryx fossils come from
the bristly filamentous feathering that weren’t for flight, but served as
insulation and for camouflage. Melanosomes, the pigment that gives coloration
to bird feathers, were found buried within the structure of the fossil
The two pigment storing melanosomes
found were eumelanosome and phaeomelanosome embedded in the protein structuring
of the feathers revealing darker striping down the tail. As melanosomes, these
two pigments are organelles enclosed by their own membrane bound in the
proteins of cells. Eumelanosome gives black pigmentation to the fossil while
the phaeomelanosome gives a burnt orange with both colors alternating down the
tail. Other colors, produced by pigments such as, carotenoids and porphyrins
add more vivid colors, but due to the fact they’re not melanosomes, they
degrade much easier over time and will not contribute to a fossil find.
Eumelanosome pigment was also found along the orbitals of the eye sockets and
nasal bridge masking the animal.
Fossilized Sinosauropteryx feathering
Along the body torso there was also
evidence of countershading with a darker dorsal side (the back) over a lighter
ventral side (the belly). This color scheme would aid Sinosauropteryx as camouflage from predators and prey with diffuse
sunlight reigning down where there is little vegetation and shrubbery to hide. Feather
coloration would have starkly shifted from dark to light, with paler plumes
running across its chest distorting an observer’s view with Sinosauropteryx and its open environment
backdrop. It is with this camouflage and its agility, quickness and speed that
gave this small dinosaur an advantage in the open sunny habitat it lived in, in
what is now northeastern China.
Sinosauropteryx fossils also
reveal that females had two oviducts instead of just one as found in birds.
This is evident in a well preserved fossil that had two developed eggs
side-by-side where two oviducts would have been.
Artist: Bob Nicholls Sinosauropteryx
Apparently, Sinosauropteryx was fond of lizards, for numerous fossils have the
remains of lizards in the digestive tract, in particular, Dalinghosaurus, which was a small lizard contemporaneous to Sinosauropteryx as found in fossil
sediment containing both animals. One fossil find had the remains in the gut
region of, Sinobaatar, a small
mammal. A further note on this little 35cm/13.8in multituberculate mammal is
that it lived beyond the Cretaceous surviving the K-Pg extinction, living into
the Eocene finally becoming extinct 34 mya. It was an arboreal herbivore that
made it as a species nearly 100 million years. When you know that, Homosapiens
have only been around for ~ 200 thousand years, Sinobaatar had quite a long success story.
is the sister group to compsognathids. Occurring 170-0 mya in the Middle
Jurassic to the present, Tyrannoraptora
is further divided into the two clades of, Tyrannosauroidea
and Maniraptoriformes (Man-ih-rap-tor-rih-formz).
Under tyrannosauroids, tyrannoraptorans are an inclusive clade to all non-avian
coelurosaurians that are more related to Tyrannosaurus
rex and under maniraptoriforms; this clade represents closer relations to Passer domesticus (the modern pigeon).
Aorun skull fossil
Two tyrannoraptorans that were not in
the direct, but as an indirect line (cousins) of tyrannosaur descendancy was, Aorun (Aw-roon) occurring 161.5mya and Ornitholestes that occurred 154 mya.
Both of these Late Jurassic tyrannoraptorans were small with Aorun no more than 1m/3.3ft long and Ornitholestes (Or-nith-oh-less-tees) at
best was 3m/9.9ft in length. Aorun is
the oldest and most primitive of tyrannoraptorans. The fossil remains were of a
sub adult that was no more than 1-yr-old, so the adult form would have been
larger than demonstrated in the fossil find from the ‘Shishugou Formation’ in a
remote part of Xinjiang, China. The fossil had very thin metacarpals in manus
digits, III and IV approximating the hands of later more derived non-avian
tyrannoraptorans. The thumb claw is large and curved while the other two finger
claws are smaller exhibiting a straight underside. The tiny skull was just
higher in height as a U.S. quarter.
Artist: Charles R. Knight Ornitholestes
Built for speed and agility, Ornitholestes did not possess any
strength for brute force as its latter day tyrannoraptorans would possess.
Chasing after small vertebrate and larger insect prey, Ornitholestes most likely didn’t use its mouth and teeth to capture
prey due to the small mouth and skull. It most likely was dependent on its
longer forelimbs to seize small prey then, once captured, deliver a killing
bite with its conical and slightly serrated frontal teeth. The back teeth were
recurved making it easier to slice through meat, so may have also scavenged on
The first major division of Tyrannoraptora is with the two sister
(Tuh-ran-o-sawr-oi-dee-uh) and Maniraptoriformes
Tyrannosauroidea ~ The temporal
range for tyrannosauroids was during the Late Jurassic to the Late Cretaceous
165-66 mya. Their special evolved features are in the skull and pelvis. Where
earlier tyrannosauroids had a long, low and lightly built skull, later forms
had taller and more massive skulls. Still there were similar distinct features,
such as possessing a very tall premaxillary bone while the nasal bones were
fused together. The tyrannosauroid pelvis had a concave notch at the upper
front end of the ilium with a sharply defined vertical ridge on the outside
surface of the ilium extending upwards from the acetabulum (hip socket). Also,
a huge ‘boot’ on the end of the pubis was more than half as long as the shaft
of the pubis itself.
Beginning in the Jurassic Period,
tyrannosauroids originated on the Laurasian supercontinent, but when Laurasia
split from Gondwana in the Middle Jurassic it left tyrannosauroid species
isolated to further evolve from the rest on the northern continents that later
separated from Laurasia during the Cretaceous. By the end of the Cretaceous,
tyrannosauroids radiated outwards becoming dominant predators in the Northern
Hemisphere culminating in Tyrannosaurus
Artist: Teratophoneus Tyrannosauroids
In more derived forms, tyrannosauroids
trended towards larger sizes and smaller forelimbs. In the more basal
tyrannosauroids, long filamentous pennaceous structures, sometimes referred to
as protofeathers and branching downy feathering were found in their fossil
remains. Downy feathering covered most of the body in these fossils finds and
was most likely used for insulation.
One of these basal tyrannosauroids with
insulation feathering features was the afore mentioned, Dilong (Dye-long). Occurring 126 mya in the Early Cretaceous, this
tyrannosauroid at 2m/6.6ft was just a bit larger than today’s average human and
at 5kg/11lbs weighed no more than a regular sized turkey. As transitional, it
is in anatomical appearance a derived coelurosaur, as well as a very primitive
tyrannosaur. In body appearance, Dilong
resembled juvenile tyrannosaurs, but had much longer forelimbs that could
support weight if it chose to stand on all fours.
Credit: American Natural History Museum Dilong
The anterior teeth of Dilong were D-shaped in cross-section
giving it a cookie cutter bite. With sure balance and dexterity as its body,
tail and hind limbs anatomically show, Dilong,
could easily reach speeds of 32kph/20mph in chasing down its prey, which likely
consisted of smaller dinosaurs and larger lizards.
Artist: Todd Marshall Timurlingia
A recent 2016 Uzbekistan fossil find in
the ‘Bissekty Formation’ of a tyrannosauroid bore out some interesting evidence
that the brain size had increased before the body size of tyrannosauroids and
later tyrannosaurs. Timurlingia
(Tim-ur-len-gee-uh) was only 3.5m/11.5ft long, but already had the brain size
of a horse according to its braincase. Occurring 90 mya in the Late Cretaceous,
Timurlingia exemplifies that
tyrannosaurs diversified upon a genus-to-genus basis with the lighter and
longer limbed hunting down more swift smaller prey and the more derived shorter
limbed genera with more brute force hunting down larger prey.
Artist: Durbed Dryptosaurus
Basal tyrannosauroids began increasing
in size evolving finally into tyrannosaurids. At 7.5 m/24.6ft, one of the last
most derived tyrannosauroids that wasn’t quite a tyrannosaurid anatomically
was, Dryptosaurus. Living 67 mya in
the Late Cretaceous in what is now the eastern USA, this tyrannosauroid’s only
anatomical disposition to tyrannosaurs was its longer forelimbs. Its larger
hands also had three fingers with 20.3cm/8in claws attached to each finger in
conjunction with surangular (all jaw bones muscularly connected) lateral teeth.
Equipped as such, this tyrannosauroid was merciless to its prey. It was also
feathered at least on the anterior body portion.
Along with, Dryptosaurus, the tyrannosauroid, Appalachiosaurus (Ah-pah-lay-chee-oh-sawr-us) are the only two
tyrannosauroids found in the eastern U.S.; the rest of tyrannosauroid fossil
finds as tyrannosaurids were found in the western half of the USA. As a
juvenile at 7m/23ft long, Appalachiosaurus’
77 mya fossil remains were found in Alabama in the ‘Demopolis Chalk Formation’.
Artist: sbpaleoartist Applalachiosaurus
The first beakdown of a tyrannosauroid
family was in the more primitive, Proceratosauridae
(Pro-seh-rat-o-sawr-ah-day) grouping. with a temporal range of of 165-120 mya
during the Middle Jurassic to the Early Cretaceous, as a family,
proceratosaurids were a difficult taxon as they had coelurosaur, ceratosaur
(hence the nomenclature) and primitive tyrannosauroid affinities in anatomy.
However, in having enough specific anatomy traits to list them as a separate
taxon, they were, through maximum parsimony and Bayesian analyses,
phylogenetically grouped together. Some main characteristics are: a cranial
crest formed by the nasal bones starting at the junction of the premaxilla and
nasals, a short and shallow concave step on the anterior margin of the maxilla,
a short ventral margin of the premaxilla, a ventrally concave ischium and just
ventral to the contact of the pubis and ilium the pubis retained a convex
Although proceratosaurids shared similar
anatomical body traits with the more derived tyrannosaurs, they were generally
smaller with distinct skull differences. First off the crests were distinct,
the dentition was odd in having small premaxillary teeth, but large lateral
teeth and the skull as a whole was highly pneumatized in the nasal, jugal,
maxillary and cranial bones. Like the primitive tyrannosauroids,
proceratosaurids also had longer forelimbs and fingers. Currently, five genera
make up the family, Proceratosauridae.
Artist: Raul Martin Guanlong
One proceratosaurid was, Guanlong (Gwon-long) which lived 160 mya
in the Late Jurassic’s ‘Shishugou Formation’ of China. The above illustration portrays a Guanlong sub-adult and adult scene of how their fossil remains were interpreted. The juvenile became trapped in a muddy watery pit, perhaps a foot track made by a large sauropod. The adult apparently attempted a rescue and became mired in the mud as well, with both dying by suffocation as the mud sunk them under. The fossil remains were found with the juvenile underneath the adult.
At 3m/9.9ft, Guanlong lived 92
million years before its relative, Tyrannosaurus
evolved. But unlike the tyrannosaurs, it had three forelimb fingers instead of
just two with the forelimbs, although shorter than the hind legs were much
longer than the tyrannosaurs. It was closer in relations to Dilong than to any tyrannosaurid. Having
found two fossils remains of a six-yr-old juvenile and a 12-yr-old adult,
paleontologists discovered that the crest was restricted to the forward portion
of the snout in the juvenile where it extended to the back of the head in the
adult. The cranial crest most likely, due to its fragility was merely for
display. There is fossil evidence that Guanlong
possessed integument feathering.
Tyrannosauridae: This is the
family that pinnacled into one of the largest and best known land predators of
all time in, Tyrannosaurusrex. Tyrannosaurids appeared in the Late
Cretaceous 80-66 mya. Although some tyrannosaurids technically support crests,
they are not as elegant or elaborate as other crested dinosaurs as either being
a row of bony bumps on the nasal bones as in Alioramus (Ah-lee-oh-ray-mus), or as a prominent horn in front of
each eye as in Albertosaurus (Al-bear-toe-sawr-us). Also, Tarbosaurus and Tyrannosaurus
had a small crescent-shaped crest behind each eye on the postorbital bone.
Tyrannosaurids essentially had binocular
vision veering away from stereoscopic vision as most actively hunting predators
in any animal group do. There is still some ongoing argument that T. rex
was more of a scavenger than a hunter due to its size hampering locomotion, but
T. rex had one of the most sophisticated forms of binocular vision
than any predator dinosaur, which would make it more of a hunter than a
scavenger, in which scavengers rely more on stereoscopic vision for depth
perception. However, Tarbosaurus did
have orbits for the eyes that faced more sideways than they did in front, but
fossil evidence proves that this tyrannosaurid relied more on the sense of
smell rather than sight.
T. rex binocular forward vision
As in modern crocodiles, tyrannosaurids
had flat snout scales that at the center were covered with small keratinized
patches. In crocodiles, these scales cover bundles of sensory neurons that
detect thermal, mechanical and chemical stimuli. It is thought that the
tyrannosaurid snout scales also covered sensory neurons to identify objects and
measure temperature ranges of their nests and to mechanically and gingerly move
eggs and hatchlings.
Tyrannosaurids were at least
homeothermic in regulating their own core body temperature putting them between
ectothermic and endothermic animals. Histological growth rates in
tyrannosaurids and in particular in Tyrannosaurus
bear out that the young had pronounced growth rates whereas in adult forms
growth halted. This is viewed in endothermic mammals and birds of today in
limiting growth only in the immature stages. Indeterminate growth as seen in
ectothermic vertebrates where growth continues throughout life is not evident
in tyrannosaurid fossils, thus through studies it appears that tyrannosaurids
maintained a constant temperature of the body’s core that was no more than 4-5
°C/7-9 °F higher than the extremities such as the tibia of the lower leg.
As in most cases though, there normally
is an exception to the rule. Albertosaurines did have a rapid juvenile growth
rate, but once reaching adulthood, although very slowly, still continued to
grow throughout the adult stage.
Tyrannosauridae is further
divided into three groups which comprise two subfamilies, one tribe, eleven
genera and thirteen species. The two main divisions are in the subfamilies, Tyrannosaurinae, orTyrannosaurine and Albertosaurinae which both are sister clades. Albertosaurinae consists of two genera in, Gorgosaurus (Gor-guh-sawr-us) and Albertosaurus with one holotype species in each genus. Albertosaurines
had a temporal range of 76.6-68 mya during the Late Cretaceous and were lightly
built with flatter skulls, shorter ilia and proportionally longer tibia when
compared to tyrannosaurines. Albertosaurine adults measured ~ 9m/30ft.
Artist: Philip Whiteley Gorgosaurus
Both albertosaurines are from what is
now N. America, with Gorgosaurus
living in lush floodplains near the inland sea of the ‘Western Interior Seaway’,
while Albertosaurus lived in areas
where the seaway had receded comprising several environments due to the
recession and transgression of the waters before the final recession. These
coastal habitats included lagoonal, estuary and tidal flat environments.
Artist: Steve White Albertosaurus
As the sister group to albertosaurines, Tyrannosaurinae includes the tribe, Alioramini (Ale-ee-ur-ray-muh-nee)
consisting of two genera and three species in, Alioramusremotus
(Ale-ee-ur-ray-mus = ruh-mo-tus), A. altai (al-tai) and Qianzhousaurus sinensis (Kin-zao-sawr-us = sigh-nen-sis). The two
species of Alioramus occurred 70 mya
in the Late Cretaceous and were from what is now the Gobi Desert of Mongolia. Q. sinensis’
almost complete remains were discovered in southern China within the city of
Ganzhou at a construction site.
Artist: Zhao Chuang Qianzhousaurus
Qianzhousaurus lived somewhere
between 72-66 mya during the Late Cretaceous, which was contemporaneous with
other tyrannosaurids that had the more typical tyrannosaurid bulky skull and
heavily muscled and powerful deep set jaws. The smaller, Qianzhousaurus at no more than 6m/20ft had to compete against these
much larger and stronger tyrannosaurids and the clue as to how it did lies in
its nickname of ‘Pinocchio rex’. This tyrannosaurid had much weaker jaws and
brute force than its other contemporary tyrannosaurids, but it had a much
longer snout. This indicates that it left the much larger prey to the other
tyrannosaurids while it filled a niche in pursuing smaller prey.
Credit: BBC Daspletosaurus
The remaining seven genera are all
direct tyrannosaurids with Daspletosaurus
(Das-plet-o-sawr-us) containing two species giving a total of eight species.
With a temporal range of 77-74 mya ago in the Late Cretaceous and up to 9m/30ft
long, Daspletosaurus species were
apex predators. They lived alongside another apex predator in, Gorgosaurus; a distinct difference in Qianzhousaurus’ situation where it
filled a lesser niche in competition with other contemporaneous tyrannosaurids,
Artist: Lukas Panzarin Lynthronax
The oldest tyrannosaurine fossil found
thus far is, Lythronax
(Lye-thru-nax), whose temporal range is in the Late Cretaceous 80 mya. This
primitive tyrannosaur was 7.3m/24ft long and had T. rex skulltraits with forward facing orbitals for
binocular depth perception as well as the skull itself being short and wide.
The serrated teeth were banana-shaped meat cleavers able to chop through the
toughest of dinosaur hides and just like T.
rex, would’ve been able to carve out
large chunks of flesh and bone to swallow whole. In being a primitive
tyrannosaurine, Lythronax had
shortened forelimbs, but were still larger than the more derived
tyrannosaurines; however, its postcranial morphology was very similar to that
of the later tyrannosaurs giving a much earlier insight into tyrannosaur
Artist: paleo executor Nanuqsaurus
Occurring 69.1 mya during the Late
(Nah-nuk-sawr-us) was a 6m/20ft tyrannosaurine theropod that lived in what is
now called the North Slope Borough of Alaska, USA. It is considered a highly
derived tyrannosaur and is the sister taxon to the clade of Tarbosaurus and Tryrannosaurus. Although temperatures weren’t as cold in northern
Alaska as they are today, Late Cretaceous Alaska, as part of the ancient
subcontinent, Laramidia would have experienced cold snowy and long periods of
dark winters. Food sources would’ve been scarce, so during the more bountiful
summer months, with its smaller size and perhaps an ability to store fat, Nanuqsaurus managed to survive the
harsher winter months supplemented by scavenging any carcasses it came
The most derived tyrannosaurines were
the two sister genera of, Tyrannosaurus
and Tarbosaurus. In fact, when Tarbosaurus
fossil remains were first found, scientists indeed thought that it was another T. rex
fossil due to the vast similarities. The main differences between the two, is
that the Tarbosaurus snout was
thinner than the wider T. rex snout and Tarbosaurus forelimbs along with total body length were a bit
Artist: James Kuether Tarbosaurus bare skin/feathered
Tarbosaurus lived 70 mya
while Tyrannosaurus lived 68-66 mya.
With both coming from Late Cretaceous, Tarbosaurus
remains come from southern Mongolia, while Tyrannosaurus
finds are from western North America. In Tarbosaurus
being older, some paleontologists have hypothesized that T. rex
evolved from Tarbosaurus, speculating
that the Tyrannosaurus taxon line
migrated from Asia into N. America from Siberia. To bear this out, more fossils
will have to be discovered and evaluated in what occurred in between the two
T. rex skin fossil
As of yet, there is no direct evidence
that either Tarbosaurus nor Tyrannosaurus possessed any type of
feather covering. But due to close phylogenetic relations of tyrannosaurids
that did possess feathers, most paleontologists consider it likely that there
were at least on some parts of the T. rex
body…feathering. Scales and scale impressions have been found in T. rex
fossils including small mosaic scales. Even bare skin impressions have been
found that would allude to feathering.
Artist, R.J. Palmer version of T. rex feathered
Back under ceratopsids we discussed a
bit on the duels we perceive that might have occurred between T. rex and Triceratops and who would win the battle as we assume a fifty
percent chance of either one winning. But we neglect the begging query as why
would T. rex fight a Triceratops
when it only had a 50-50 chance? The deal is...T. rex wouldn’t. He or
she would only fight Triceratops if
the odds were in its favor. It most definitely was and here is why...
Artist: Vlad Konstantinov T. rex vs. Triceratops
T. rex had a bite force of 562.5kg/sq. cm
or 8,000 lbs/sq. in, while in the initial bite, the teeth’s tip exerted an
astounding 30,302.3kg/sq. cm or 431,000 lbs/sq. in. That’s equivalent to the
same pressure as having 33 full grown African elephants stacked atop one
another atop your head. With this biting force supplemented by sixty razor
sharp 30.5cm/12in serrated teeth, T. rex could slice through any tough dinosaur
hide and chomp through bone to get at the marrow. So in getting back to the T. rex/Triceratops battles mentioned earlier
under ceratopsids, in one quick bite hold, T.
rex could have easily sliced through
and severed Triceratops head and
flung it; with a frill or no frill.
Simple Maniraptoriformes Cladogram
Maniraptoriformes ~ Quickly
radiating out into new lands, basal coelurosaurs were predators of various
Jurassic and Cretaceous environmental biomes. This created a rapid
diversification and evolvement to fill in niches that never before were
available to theropods. It also generated omnivorous and even herbivorous
theropods filling in regions where small herbivores were absent. In regions
where there were large herbivores but no large carnivores, the smaller
theropods began enlarging their bodies. In ecology, this is known as ‘niche
partitioning’ and is the process by which competing fauna utilize a biome
differently than another species allowing a steady coexistence. This is the
setting where the maniraptoriforms’ story unfolds.
As the sister taxon to Tyrannosauroidea, maniraptoriforms
consist of two clades in Ornithomimosauria
(Or-nith-uh-my-mo-sawr-ee-ah) and Maniraptora
(Man-uh-rap-tor-ah). Maniraptoriforms had a temporal range from the Late
Jurassic to the present from 167-0 mya. Maniraptoriforms consist of the clades
that led directly to birds.
According to the cranial portion of the
skulls, maniraptoriforms contained in the clade, Maniraptora (Man-uh-rap-tor-uh), all had brains that were at a
minimum twice as large as the more basal coelurosaurs. Typical features are in
having small phyllodont (leaf-shaped) teeth or no teeth at all in the more
derived and, except for the most basal, often lacked grabbing claws, or no
claws at all in the more derived. This would suggest that early in their
evolvement, maniraptoriforms were trending on the whole toward an herbivorous
diet. They all possessed feathering, even in some, broad pennaceous feathers
branching off from a shaft. The tiny alvarezsaurid, Shuvuuia (Shu-vue-ee-ah) possessed a form of keratin consistent to
that of modern day birds, while the ornithomimosaur, Pelecanimimus (Pel-ee-can-eye-mime-us) fossil finds bear impression
evidence to the skin’s collagen fibers suggesting that under a feathered cloak,
the body was without scales just as in birds.
Ornithomimosauria ~ Called
ornithomimosaurs, or ornithomimosaurians, but commonly known as ‘ostrich
dinosaurs’ occurred 140-66 mya during the Early-Late Cretaceous. They are the
most basal of maniraptoriforms with their taxa line coming to an end 66 mya.
Compared to the large eyes the skulls were small. While they experienced a
reduction in tooth size, the slender necks lengthened. The forelimbs were also
long with the manus distal ends terminating into powerful hooked claws, used
most likely for reaching and grasping. The hind limbs were also long and
powerful with the pes (feet) ending in hoof-like claws making ornithomimosaurs one of
the swiftest of dinosaur runners. Even though there are numerous fossils
detailing ornithomimosaurs as prey, with their hind limbs, they weren’t totally
defenseless. Just as ostriches can today in gutting a lion or even a human with
their pes claws, the larger ornithomimosaurs could have done the same to their
predators. Even a well-placed kick could do damage.
Judging from ornithomimosaur fossil
finds containing gastroliths, for the most part, it alludes to the fact they were herbivores, but some could also have been omnivores preying on small
vertebrates and large invertebrates such as insects.
Ornithomimosaurs make up for a large
group of species, with nine holotype genera and with two families in Deinocheiridae (Dee-in-no-care-ah-day)
having three genera and Ornithomimidae
(Or-nith-o-mi-muh-die) having eleven genera.
Found in South Africa’s ‘Kirkwood
Formation’ that was laid down during the Early Cretaceous, Nqwebasaurus (Nuh-qway-ba-sawr-us) from 140 mya is the most basal ornithomimosaurian
found thus far. As the earliest ornithomimosaur and coelurosaur from Gondwana,
it was a 90cm/35.4in long three-year-old subadult. It had small reduced teeth
and utilized gastroliths for digesting plant material. The hands were
three-fingered including an opposable tipped with a claw. The well preserved
fossil remains were found in the ‘Kirkwood Formation’ of South Africa making it
the only African coelurosaur found.
Artist: Riley Chandler Nqwebasaurus
The ‘mimo’ in Ornithomimosauria refers to the Latin word, ‘mimicus’ meaning
mimic. So, Ornithomimosauria, means
‘bird mimic’, which in essence means they appeared to be birds but weren’t.
Tooth reduction is an obvious evolutionary pattern in ornithomimosaurs, with Nqwebasaurus having reduced teeth as
compared to other contemporaneous coelurosaur groups, while the latter
ornithomimosaurian holotypes in the 130 mya Pelcanimimus
(pelican mimic) had more reduced teeth than Nqwebasaurus
and the 130 mya, Harpymimcus (harpy
mimic) only had small cylindrical teeth in the lower jaw. By the time the
ornithomimid, Gallimimus (chicken
mimic) arrived 70 mya, its beak was totally toothless.
occurred between 115-66 mya during the Late Cretaceous of Asia. Best known for
their forelimbs, deinocherids had the longest arms of any other biped theropod.
In general body anatomy, they were bulky but lightweight due to hollow bones.
The three genera that make up the family are: Bishanlong (Bay-shan-long) from the ending of the Early Cretaceous
115-100 mya, Garudimimus
(Gah-rue-die-mime-us) from the beginning of the Late Cretaceous 98-83 mya and Deinocheirus (Dee-in-no-care-us) from
the ending of the Late Cretaceous 71-69 mya.
Artist: Damir Martin Deinocheirus
The largest ornithomimosaurian was the
deinocheirid, Deinocheirus at
11m/36ft long while weighing 6,350kg/14,000lb. The Gobi Desert fossil finds in
Mongolia prove this ornithomimid to be one unique theropod. Most
ornithomimosaurs were lithe built for speed, but this huge humpbacked
ornithomimosaur was a slow moving gargantuan. It also had a duck-billed shape
beak mounted on a horse-shaped skull. The last twelve back vertebrae supported
bulky neural spines that became increasingly longer from front to back with the
last one being 8.5 times longer than the centrum portion. This made the central
to rear half of the back look hump-like. The spines supported interconnecting
ligaments supporting the large abdomen. The forelimbs are the largest of any
Deinocheirus fossils have
been found in sediment that were near rivers, small lakes and in mudflats. With
at least 1,400 gizzard stones 8-87mm/0.32-3.3in in diameter found in fossil
remains and also with the large abdomen, Deinocheirus
ate soft plants and in particular with the duck-billed snout it foraged for
water plants and browsed near the ground. It had no teeth but fish vertebrae
and scales have been found mixed in with the gastroliths and whether the fish
were ingested incidentally or not, makes it an omnivore. The musculature
working the jaws were weak, so if it preyed on any land animals they would’ve had
to been small, as the jaws were too weak to seize any prey with any larger size
to it. Deinocheirus also had
vertebrae spines in the middle of the back that supported a hump and like
camels, it presumably stored fat.
Ornithomimidae is the last of
the two families of ornithomimosaurians to radiate out into its own group. With
a temporal range confined to the Late Cretaceous 92-66 mya, ornithomimids are
known for their ostrich-like appearance in having large eyes, small heads and
relatively long slender necks. With muscled long hind limbs, the legs were
powerful terminating in a long foot with short but strong toes bearing
hoof-like claws. As mentioned earlier, ornithomimosaurs were the fastest of
dinosaurs, but ornithomimids were the fastest of ornithomimosaurs. The body’s
skin was feathered rather than scaly.
Artist: Mohamad Haghani Struthiomimus
Another ornithomimid besides the
aforementioned, Gallimimus was, Struthiomimus (Stru-fee-o-mime-us) which
stands for ‘ostrich mimic’ and had a temporal range of 77-66 mya towards the
end of the Late Cretaceous. At 4.3m/14ft long and 1.4m/4.6ft tall, Struthiomimus was the fastest runner of
ornithomimids, therefore the swiftest of all dinosaurs with anatomical studies
showing maximum speeds of up to 80kph/50mph. Struthiomimus was a gregarious herbivore. The anatomy supports an
herbivorous diet in that the structure of the shoulder girdle was construed as
to not allow the arms to reach in elevation, nor was the shoulders optimized
for reaching to the ground. The II and III manus digits were equal in length
and could not function independently suggesting that in life they were bound to
work as a single unit by skin covering. The whole manus (hand) could not be
fully flexed, so all this alludes to the fact that the manus was used as a hook
and clamp for bringing plant material in reach of the mouth. This hand
adaptation would also have served as the forelimb’s wing feather support.
Maniraptora ~ Genetically
borrowed from their coelurosaur ancestry, maniraptorans and early birds
inherited an increase in the size of the brain’s proportion devoted to the
cerebrum. The cerebrum is that part of the brain responsible for the
integration of complex sensory and neural functions and the initiation and
coordination of voluntary activity in the body. However, there was much
convergent evolution in maniraptoran groups as well, but have enough
synapomorphies (common anatomical structures) to be phylogenetically united. With
this understanding, keep in mind that maniraptorans as deeply nestled within
coelurosaurs, are a branched clade closer in genetic relations to extinct and
extant birds than they are to ornithomimosaurs.
Typical maniraptoran anatomical features
were: a fused clavicle (shoulder blade) and sternum (breast bone), a bird pubis
that points downwards rather than forwards, a shortened or absent tail ending
in a stiffened pygostyle, a manus (hand) longer than the pes (foot) in the most
derived and are feathered. With a unique modified wrist bone found only in
maniraptorans called the, ‘semi-lunate carpal’ it originally made the wrist
more flexible, but later on in the most derived maniraptorans, it made it
possible for flight. Thus, the maniraptoran clade contains the only group of
dinosaurs that evolved the capability of flight.
The temporal range for maniraptorans is
from the Late Jurassic 167-0 mya. The major clades of maniraptorans are the: alvarezsauroids,
therizinosaurs and the pennaraptorans which includes the avialan groups in
which birds are a part of.
Artist: Matthew Martyniuk Some alvarezsauroid sizes
The most basal of maniraptorans are from
the clade, Alvarezsauroidea
(Al-vuh-rez-sawr-oid-dee-ah) occurring in the Late Jurassic to the Late
Cretaceous 160-66 mya. The oldest and most primitive alvarezsauroid is Haplocheirus (Hap-lo-chair-us) predating
any other maniraptoran member species by 63 million years. It roamed through
the Late Jurassic northwestern China semi-arid lands 260 mya. Haplocheirus was ~ 2m/6.6ft long with
fossil exposing an almost complete individual. It had not yet developed the
specific developed manus (hand) as the more evolved Cretaceous South American
and Asian maniraptorans show with the singly enlarged digit as it still
retained the use of two fingers with a well-developed thumb that became
vestigial on most of the latter maniraptoran forms. It was covered in downy
insulating feathers and possessed a deep keel (extension of the sternum). With
long legs ending in three toes it was a swift runner and walked in digitigrade
(walking on toes) fashion just as birds do.
Artist: Portia Sloan Haplocheirus
Like most Jurassic theropods, Haplocheirus had relatively normal-sized
curved and serrated front maxillary teeth. But the distinguishing dentition
feature is that the back teeth rapidly decreased in size while the roots of the
teeth became circular in cross section. There were at least 30 teeth in the
maxilla and judging by this, Haplocheirus
most likely preyed on small animals and larger insects.
All other alvarezsauroids belong to the Alvarezsauridae family. This family is
comprised of twelve genera with the two subfamilies, Patagonykinae (Pat-ah-go-nee-key-nee) and Parvicursorinae (Par-vye-kur-sor-uh-nay) in which has the two
(Suh-rat-toe-nee-key-nee) and Mononykini
(Maw-no-nee-key-nee). Alvarezsaurids had a temporal range of 89-66 mya during
the Late Cretaceous. Evolving from a primitive maniraptoran branch,
alvarezsaurids were trending toward smaller body sizes and shorter forelimbs
with Parvicursor (Par-vee-kur-sor)
being no longer than 39cm/15.4in when fully grown. Alvarezsaurids only had one
developed digit ending in a large claw. The other fingers, except in Linhenykus were vestigial nubs. This
claw is presupposed to have been used in digging for insects, in particular to
dig through termite mounds. Although the forearms were significantly short, the
strong arm and breast muscles were adapted for tearing and digging.
Artist: Ezekiel Vera Parvicusor
members are composed of the largest alvarezsaurids, with Patagonykus (Pat-ah-go-nee-cuss) at 2m/6.6ft in length and Bonapartenykus (Bo-nuh-par-tuh-nee-cuss)
at 2.6m/8.5ft long. Both occurred in what is now, the Patagonia region of
Argentina during the Late Cretaceous, with Patagonykus
from ~ 89 mya and Bonapartenykus from
72 mya. They were primarily insectivores but also could handle small vertebrate
prey. Both Patagonykinae and Parvicursorinae members came from a
common coelurosaurian ancestor when their respective continents were connected
and diverged when continental drift separated them.
Patagonykus skeletal anatomy
Patagonykus is a basal
alvarezsaurid anchoring the subfamily, Patagonykinae.
With primitive features for an alvarezsaurid, the last sacral centrum is
ball-shaped caudally, a condition that is also found in the caudal vertebrae
like the earlier coelurosaurs. But it possessed the derived alvarezsaurid,
‘pinched’ middle toe.
Artist: Gabriel Lio Bonapartenykus
Bonapartenykus fossilized egg
An interesting feature of Bonapartenykus’ fossil remains is two
eggs that were still retained in the oviducts of the female individual. Nearby
of the specimen fossil site were found a nest of eggs that were contaminated
with a fungus that killed the eggs; a clue that the mother had died post to
just laying the eggs and unaided, the eggs were exposed to the fungal
infection. The eggs are very unique dinosaur eggs and thus have been
categorized under the oogenus (fossil eggs), Arriagadoolithus.
Artist: Karkemish Alvarezsaurus
Alvarezsaurus is the sister
member to the subfamily, Parvicursorinae.
As a basal alvarezsaurid it had a longer tail, a curved scapula, an unfused
astragalus and calcaneum unlike the more derived alvarezsaurids, but possessed
typical alvarezsaurid features in its limb structures and its caudal vertebrae.
It came from Late Cretaceous Argentina 86-83 mya.
(meaning: small runner) tribe members were all small swift sprinters. The name
refers to an arctometatarsalian condition where the middle metatarsal (MT-III)
is extremely pinched by the flanking two, MT-II and MT-IV. All were most likely
primary insectivores, but with their minute pegged teeth they possibly could
have snagged very small vertebrates and gulped them down as the jaw muscles
were too weak to contend with any animal of size. They all occurred during the
Late Cretaceous of Asia and N. America 84-66 mya.
Parvicursor is the only Parvicursorinae member that does not
belong to a tribe but is the holotype sister to the tribe, Mononykini. Living 72 mya in the Late Cretaceous only weighed ~
162g/5.7oz and as previously mentioned, was 39cm/15in in total length; pretty
small considering our preconceived notion of dinosaur size.
Artist: Nobu Tamura Ceratonykus
Ceratonykini is comprised of
Ceratonykus (Suh-rat-toe-nee-cuss), Xixianykus (Zee-ee-awn-ee-cuss) and Albinykus (Al-bin-e-kus) where all
members are most related to the last common ancestor of Ceratonykus.Ceratonykus was 1.5m/4.9ft in length and
with long legs was adapted to running in desert habitat. Xixianykus was 50cm/20in long and with legs that were 20cm/8in
long, it had the longest leg to body ration of any dinosaur. Albinykus’ length is unknown due to
incomplete but well preserved fossil remains. However, in life it could have
stood comfortably fitting neatly in the palm of a human hand. The fossil
remains were positioned in a crouching position with feet tucked underneath the
body much like birds do today. Apparently a sand-slide doomed the individual
Artist: Matt van Rooijen Albinykus
Mononykini is comprised of
Mononykus (Maw-no-nee-cuss), Albertonykus (Al-bear-toe-nee-cuss), Linhenykus (Lin-he-nee-cuss) and Shuvuuia (Shu-vu-ee-ah). Mononykini members are more closely
related to the common ancestor of Mononykus
than they are to other alvarezsaurid species. Mononykini species all lived between 84-68.5 mya during the Late
Cretaceous coming from what is now Asia and North America.
Artist: M. Haghani Mononykus
Occurring 70 mya in the Late Cretaceous
Mongolian floodplains, Mononykus was
nimble and with a light skeleton and long legs was built for speed, which was
useful on the flat mainly featureless terrain it lived in. With large eyes, it
most likely sought out prey during cooler darkness when most of its predators
were inactive. Prey consisted of insects and small vertebrates that it could
snag with its small pointed teeth. It had a long thumb spike in digit I of the
manus (hand) and a pubic bone that was triangular in cross section. In the
pelvis, the ischium and ilium were fused together
Mononykus skeletal anatomy
Artist: Karkemish Albertonykus
Albertonykus occurred 68.5
mya during the Late Cretaceous with its fossil remains coming from the
‘Horseshoe Canyon Formation’ of Alberta, Canada. It measured only 70cm/2.5ft in
total length. It also preyed on termites, but not the mound termites as the
Asian alvarezsaurids did, as mound or earthen termites did not appear in N.
America until the Eocene. As Albertonykus
had arms too short for digging, they however would have been ideal for breaking
the bark of trees to get at wood termites that were present in N. America as
attested to termite burrows in petrified wood that lived during Albertonykus’ time. It surely would have
accepted any other bark-living insects along with their grubs and larvae. Albertonykus is a pertinent fossil find
for it supports the fact that alvarezsauroids originated in S. America then
dispersed to Asia with the more derived species migrating to N. America when
the continents were connected.
Artist: Julius T. Csotonyi Linhenykus
Occurring, ~ 79.5 mya years ago in Late
Cretaceous Mongolia, Linhenykus at
90cm/35.4in was a typical small alvarezsaurid with its single digit II long
finger ending in a heavy claw. But rather than having any vestigial digit nubs
it had no remnants of any other digits; all other digit metacarpals were
absent. As a latter basal alvarezsaurid, Linhenykus,
in retaining some archaic features, but having some distinct characteristics
unique among its own from the more derived species represents a mosaic pattern
in evolution. It most likely was an insectivore.
With a temporal range of 75 mya in Late
Cretaceous Mongolia, Shuvuuia was no
longer than 60cm/2ft long. Its forelimbs were unusually short but terminated with
the manus supporting a massively enlarged digit I (thumb) and not quite
vestigial, but reduced digits II and III. Living in localized fluvial plains of
what is now the Gobi Desert, Shuvuuia
scampered about chasing down insects or small vertebrates it could seize with
its minute teeth that weren’t serrated or capable of biting into tough flesh.
Once prey was captured it would be swallowed whole. It also, as other
alvarezsaurids, most likely used the singular manus claws to dig into termite
Unique among the non-avian dinosaurs, Shuvuuia’s lightly built skull was
capable of performing prokinesis where the upper jaw can flex independently of
the skull’s braincase. One fossil find showed that the body was coated with
small hollow tube-like structures resembling the rachis (central vane) of
modern bird feathers.
Artist: Nattawut Wongta Shuvuuia
is very similar to Mononykus, but differs
1) in having cervical centra less compressed laterally bearing large pneumatic
foramina, 2) deltopectoral crest of humerus continuous with humeral head, 3)
femoral and tibiotarsal shafts bowed mediolaterally, 4) medial border of distal
end of tibiotarsus with a sharp ridge, 5) medial margin of the ascending
process of the astragalus less notched with lesser degree of co-ossification of
proximal tarsals and metacarpals.
Just to mention, there are two more
alvarezsaurids that are not as yet fully classified. The first is, Alnashetri (Al-nah-shet-ree) that
occurred during the Late Cretaceous 97 mya in what is now the northern edge of
Patagonia. Its age makes for it to be a primitive alvarezsaurid and its
location puts it nestled within the Patagonykinae
tribe. However, the inclusion is based on a polyatomic phylogeny within a
single anatomical region of the ankle and may create false results.
The genus, Kol with the species name, K.
ghuva (gah-vuh) is a recent Mongolian
fossil find represented by a well preserved foot displaying the typical arctometatarsalian
‘pinched’ middle toe. It is an alvarezsaurid, but until more fossil
discoveries, it isn’t clear to what tribe it belonged to.
Ther-ih-zign-o-sawr-ee-ah) ~ The therizinosaurian clade order is composed of
one superfamily, Therizinosauroidea
and one family, Therizinosauridae.
Within the whole clade there are 12 genera and 14 species. In the genus, Nanshiungosaurus (Nan-she-ung-sawr-us)
there are currently listed two species in, N.
brevispinus (bre-vis-pi-nus) and N. bohlini
(boh-lee-nee), but with N. bohlini being much older and larger, it
may later be designated its own genus. The therizinosaurian temporal range is
from 130-70 mya during the Early-Late Cretaceous.
Artist: Raul Lunia Therizinosaurus
For sure, among all the picks to choose
from, therizinosaurs are the oddest of dinosaurs. First off, they came from
flesh eating coelurosaurian theropods, even though a feast for them would be a buffet
filled with dandelions, cycad leaves and conifer needles. They evolved the
longest necks of any theropod and long forearms ending in the longest claws of
any dinosaur, which were used for grasping vegetation and secondarily for
ripping the guts open of an offending predator. The forelimbs also had a unique
range of motion allowing therizinosaurs to have the farthest forward reach
degree of any other known theropod. Another unique feature is that from shortened
metatarsal foot bones, the more derived therizinosaurians began walking on four
toes instead of the theropodal three middle toes.
Even though the skulls were small, CT
scan results of fossil skulls show that therizinosaurs had an acute sense of
smell, hearing and balance. The torsos were wide and with unique hipbones
pointing backwards, were one of the first theropods to develop the familiar
‘bird-like’ pubis, even though they are a non-avian maniraptoran.
Therizinozaurians lived in lush forests of Eurasia North America with latter
species moving into more harsh tundra regions.
Falcarius skeletal anatomy
Artist: Apsarvis Falcarius
The most basal therizinosaurian was, Falcarius (Fal-care-ee-us) that had a
temporal of 126 mya during the Early Cretaceous. In Falcarius, the elongated neck and forelimbs were already an
attribute. Its dentition alludes to an omnivorous diet, although the
leaf-shaped teeth point to the transitioning of a more herbivorous diet. This
therizinosaurian, at 3.7-4m/12.1-13.1ft long was much smaller than the more
derived forms in which some latter species would top over 9.1m/30ft.
As a sister to therizinosauroids, Jianchangosaurus (Jee-en-chan-go-sawr-us)
occurred 126 mya in the Early Cretaceous and is considered more derived than Falcarius, but more primitive than the
basal therizinosauroid, Beipiaosaurus.
It was another smaller therizinosaurian measuring only 2m/6.6ft long, but had
fully made the transition over to an herbivorous diet. The dental morphology in
which the tooth surfaces facing the outside of the mouth is convex, teeth on
the lower jaw possesses the reversed morphology, where the surface of the tooth
facing the outside is concave. This maximized biting stresses during occlusion
in cutting and masticating fibrous plant material.
Artist: Masato Hattori Suzhousaurus
(Be-o-pee-uh-sawr-us) is the basal most primitive therizinosauroid and is from
the Early Cretaceous 124.6 mya. From direct fossil evidence, Beipiaosaurus is one of the largest
dinosaurs in possessing feathered covering and had the longest feathers of any
dinosaur yet found. There were two kinds of feathering with a downy covering
and the very large 12.5cm/5in quilled feathering that rose up through the down.
Reaching a length of 2.2m/7ft, it still had reduced inner toes, but the fourth
was enlarging, therefore transitioning to the four toes latter forms were
walking on. The only teeth it possessed were in the cheek portion of the jaws. Its
head and toothless beak were also larger than the more derived forms with the
skull measuring about as large as the thighbone.
Credit: Anness Publishing Nothronychus
The therizinosaurid family consisted of
five genera with two Nothronychus
species making for six species total in the family clade. The family temporal
range was 94-66 mya during the Late Cretaceous. All therizinosaurid species
possessed four weight bearing walking toes and the characteristic opisthopubic
pelvis.Suzhousaurus (Suz-how-sawr-us), living in the Early Cretaceous ~
113 mya, was sister to and basal to the therizinosaurids. It lived in what is
now China and is the closest relative to the two species in the N. American, Nothronychus (Noff-ron-ee-cuss) genus.
This primarily verifies that therizinosaurs, along with other dinosaurs,
regularly traversed a transitory land bridge connecting Asia to North America.
Therizinosaurs were already enlarging body size in, Suzhousaurus, which had reached 6.5m/21ft in total body length. The
distinguishing feature of, Suzhousaurus
was its anteriorly straight and flattened ilium while the flattened pubis
curved forward forming a shaft that had a hollow front edge.
Artist: dinoraul Therizinosaurus
Therizinosauridae fossilized manus
Artist: Vlad Konstantinov Therizinosaurus
Therizinosaurus, in being the
namesake of Therizinosauridae and therizinosaurians
overall, was the most derived and largest form of therizinosaurians. It had a temporal
range of 70 mya in the Late Cretaceous. With a bulky body and perhaps lumbering
gait walking on four digits, in which digit one was reduced to a dew claw, it
reached a length of 10m/33ft, making them not only the largest
therizinosaurian, but also the largest maniraptoran. Found only in the earlier
and contemporaneous ornithischians and contemporaneous and later bird-line, Therizinosaurus had a fully developed
opisthopubic (pubic bones pointing backwards) pelvis. At 1m/3.3ft, it also had
the longest claws on each of the three digits of their forelimbs than any other
dinosaur. In fact, in ignoring claw to body size ratios, the Therizinosaurus claw is the largest of
any known animal. If we do look at body size ratio, Therizinosaurus with a 8.2-10% body/claw ratio, then today’s
armadillo mops that up with a 22% body/claw ratio. The point is that Therizinosaurus had the biggest
Artist: Paval Riha Therizinosaurus fetus
Therizinosaurus’ were large
herbivores competing for plant food with various sauropods in what is now,
Mongolia. Seventeen clutches of Therizinosaurus
eggs were found in near proximity of one another in the Gobi Desert and points
to the fact that Therizinosaurus was
indeed social and gregarious; at least during nesting.
Therizinosaurus fossilized eggs
In the maniraptoran clade, therizinosaurs
were the sister group to pennaraptorans. As defined, the clade, Pennaraptora (Pen-nuh-rap-tor-ah) is the
most recent common ancestor of Oviraptor
antirrhopus and Passer domesticus
(the house sparrow), along with all descendants thereof. The temporal range for
pennaraptorans is from 167-0 mya during the Jurassic to the present. Anchiornis (An-chee-or-niss) occurring
160.89-160.25 mya during the Late Jurassic, so far is the earliest
Simple Pennaraptora Cladogram
Although it represents a very small
portion of the dinosaur form, the pennaraptoran order, Oviraptorosauria (O-vye-rup-tore-o-sawr-ee-ah) is comprised of at
least 33 genera, 36 species and with 3 extra species listed as suspect
oviraptorosaurian but not diagnostic, so are ‘nomen dubium’ due to scant fossil
material. There is one primitive family in, Caudipteridae
(Kaw-dee-tear-ah-day) one superfamily in, Caenagnathoidea
(Suh-nawg-nah-thoi-dee-ah) that contains the two families, Caenagnathidae (Suh-nawg-nath-uh-day) and Oviraptoridae (O-vee-rap-tor-uh-day).
If someone today spotted an
oviraptorosaurian they would swear they saw a bird, but they did not. The
temporal range for oviraptorosaurians was 130-66 mya all in the Cretaceous
Period. They are close relations to birds but did not form a direct line. They
could not fly, but were fully feathered, except for the hind limbs, which were
scaled like modern birds. Even though the shortened tails did not end in a
pygostyle like birds, it was fully feathered with a bony structure at the
distal end of the tail that acted much like a bird’s pygostyle in supporting
long flight tail feathers. The ulna (long forearm bone) also was quilled with
They had evolved shortened rostrums
(snouts), massive beak-like mandibles, extensive pneumatized skulls with the
more primitive forms having only four pairs of premaxillary teeth while the
latter forms had no dentition. Some supported a bony crest atop the skull. The
forelimbs were ~ half the size of the hind limbs while the manus (hands) were
long and tridactyl.
Artist: Matt Martniuk Caudipteryx
Most oviraptorosaurians were no more
than 2m/6.56ft long and ranged in size from, Caudipteryx (Caw-dip-teh-rix) at 1m/3.3ft long to Gigantoraptor (Gye-gan-toe-rap-tor) that
was by far the largest oviraptorosaurian at 8m/26.3ft long. Even so that most
were small, they all had a massive and large shoulder girdle when ratioed to
Artist: M. Haghani Gigantoraptor
with a temporal range of 126.4 mya in the Early Cretaceous is either the
precursor to oviraptorosaurians or is the most primitive of this order clade. In
fact, it is closely related to Incisivosaurus
and if more fossils are found, they may even be one and the same, or at least
in the same genus. Coming from what is now China, its anatomy had hollow bones,
a furcula (wishbone), long legs for running and although the manus (hands)
supported three fingers ending in sharp curved claws similar to its
coelurosaurian carnivorous predecessors, it most likely was an herbivore or at
best an omnivore.
At 1m/3.3ft long, Protarchaeopteryx was the first dinosaur fossil find with solid
proof of dinosaur feathering back in 1996, with the fossil exhibiting fine
detail. They were not flight feathers, but were vaned symmetrically on the
short tail and extended feathers were on its forearms. The body feathering most
likely for insulation and the tail and forearm feathering was for display. All
extant flightless birds have symmetrical tail feathers and Protarchaeopteryx’s skeletal structuring would not have supported
flight. However it may have endeavored an arboreal lifestyle jumping from limb
to limb and parachuting to the ground.
As a bit of a conundrum, the name, Protarchaeopteryx literally means
‘before Archaeopteryx’. The only
problem with that is Archaeopteryx
lived ~ 25 million years before Protarchaeopteryx
ever showed up in the fossil record. Don’t be too alarmed, for this isn’t a
glitch. This is quite possible in the fact that both came from a common
ancestor with Archaeopteryx evolving
at a much quicker pace than Protarchaeopteryx’s
more direct phylogeny. Look at horseshoe crabs, which really aren’t crabs in
belonging to the subphylum, Chelicerata
and in being so, are more related to spiders. But where horseshoe crabs, who’ve
virtually remained unchanged physiologically and anatomically for the past 450
million years, the spider lineage has seen its line go from aquatic livelihoods
to terrestrial ones and have diverged into nearly 40,000 species.
Artist: Pablo Lara Incisisvosaurus
The earliest oviraptorosaurian so far
discovered is, Incisivosaurus
(In-sise-ee-vo-sawr-us). Occurring 126 mya in the Early Cretaceous, Incisivosaurus had a mouthful of
variant teeth consisting of molars, premolars, incisors and canines for
breaking into and grinding hard plant food material. The premaxillary bones
anchored two large bucktoothed incisors used for gnawing much like today’s
rodents. These prominent incisiform buckteeth is what gives this dinosaur its
Credit: Eudagraphics Insisisvosaurus head/skull
The dentition of Incisivosaurus would not have been adequate enough for a carnivore,
so it can safely be said it took up an herbivorous diet of rough foods from
nuts, twigs, saplings and tough cellulosic leaves. It used the buckteeth for
gnawing at cellulosic material and probably to crack nut-like food to get at
the seed contents. The molars were for masticating to initiate digestion. It
also swallowed small stones to utilize as gastroliths.
Coming from what is now China, Incisivosaurus was 1m/3.3ft long and is
included as the possible primitive ancestor to the more derived oviraptorosaurians.
With a short cervical (neck) and slender lower jaw supporting a long fenestra
this transitional maniraptoran shared in the traits of more derived
oviraptorosaurians, while retaining more primitive ornithomimosaur features
with reduced olfactory lobes and expanded optic lobes. This Incisivosaurus transitioning illustrates
that many of the avian traits were not present in early members of the oviraptorosaurian
group. This slices oviraptorosaurian away from the direct line of birds proving
that the bird-like characteristics among later oviraptorosaurs were convergent
Artist: Emily Willoughby A Caudipteryx family
Occurring 124.6-120 mya, the most basal
family of oviraptorosaurians was, Caudipteridae
(Caw-dee-tear-ah day) with fossils found in Early Cretaceous China from the Yixian
and Jiufotang Formations. The distinguishing characteristic, besides full body
downy feathering was a unique styled dagger-like pygostyle which anchored a fan
of quilled feathers. There are three species in the family in being, Caudipteryx zoui, (Caw-dip-tuh-riks =
zoo-we) C. dongi (dawn-gey) and Similicaudipteryx
yixianensis (Suh-mil-uh-caw-dip-tuh-riks = see-icks-e-in-nin-sis). With
minor differences between species such as body size, forearm primary feather
lengths, breastbone size and minor variations in the forelimb and hip bones,
caudipterids were very similar in anatomy, possessed long sharp and bulbous
deep rooted dentition and along with gastrolith fossil finds suggest an
omnivorous diet. C. zoui was the largest at 1m/3.3ft, C. dongi
was .70m/2.3ft long and S.yixianensis was ~ 1m/3.3ft in length.
The 3 Caudipteryx species
With pennaceous and symmetrical tail
feathers and forearm primary and secondary feathers, caudipterids could not fly,
utilizing instead long hind limbs for moving the light body via swift running.
However, no matter if they couldn’t fly, caudipterids were exhibiting a
transitional progression towards feathered flight putting them into a more
direct line to birds. Similicaudipteryx
juvenile fossil specimens have been found and exhibit the characteristic
caudipterid feather traits of downy body coverings and symmetrical vaned
feathering on the tail and forelimbs. The vane feathers of the juvenile fossils
though, showed a ribboning effect in the vane feathers.
As an expert in bird feather development,
Richard Prum studied the fossils and explains that the apparently ribbon-like
structure of the juveniles’ feathers were consistent with pennaceous feathers
in the midst of moulting. In modern birds, new vaned feathers emerge from the feather
follicle enclosed in a ‘pin feather’, which is a solid tube covered in keratin.
Usually, the tip of this tube will fall away first, leaving a structure
identical to that seen in the Similicaudipteryx
fossil. Later, the rest of the sheath falls away when the entire feather has
Prum also noted, as did Xu and his team
who unearthed the fossils, that the structure of the Similicaudipteryx feathers is fundamentally different from other
prehistoric birds with ribbon-like tail feathers. In those other species, the
ribbon portion is formed from a flattened and expanded rachis (central quill)
of the feather, with the feather barbs expanding out at the tip. In Similicaudipteryx, however, the ‘ribbon’
portion is the same width as the vaned tip. This is consistent with what is
seen in bird feathers in the process of moulting. Prum concluded that rather
than representing an instance of feathers changing in form as the animal aged,
this specimen represents the first known fossil evidence of feather moulting.
Artist: Sydney Mohr Similicaudipteryx
Remiges (bird wing flight feathers) and
retrices (Bird tail rudder flight feathers) had already evolved in caudipterids
even though the feathering first served as display and insulation rather than
The superfamily, Caenagnathoidea (Suh-nog-nah-thoi-dee-ah) has one basal
caenagnathoid and two family groups that ranged from 125-66 mya during the
Cretaceous and lived in what is now N. America and Asia. The main features were
in the skull that supported short parrot-like beaks and often times a bony
crest atop the cranium. They are defined as the descendants of their two most
recent ancestors, Oviraptor
(O-vur-rap-tur) and Caenagnathus
This superfamily is characterized by
members having the sacral centra and caudal centra possessing pleurocoels,
which are a set of hollow depressions on the vertebrae’s lateral portions.
Also, the skull displays a fused mandibular symphyses with the mandibular rami
as bowed mid-length from a dorsal view and the rostrodorsal (region near back
of the beak) margin of the dentary (anterior bone of lower jaw) is concave
while the palatal shelf of the maxilla has two longitudinal ridges with a
tooth-like ventral process.
Artist: Apsaravis Avimimus
The most basal caenagnathoid was Avimimus (A-vee-my-mus) that occurred in
the Late Cretaceous 70 mya in what is now Mongolia. At 1.5m/4.9ft long it was
very bird-like in appearance. It did possess very small premaxillary teeth and
was either an herbivore, or insectivore or both as an omnivore. The foramen
magnum (the hole in the skull allowing the cervical column to connect with the
brain was proportionately large compared to the rest of the skeletal anatomy.
The hind limbs ended in bird-like three toes and the forelimbs were short with
the manus (hand) bones fused together as it is in birds today. Due to the
ilium’s position being oriented almost horizontally, the hips were exceptionally
broad and anchored a long tail. This is the primary reason in the thinking that
it couldn’t fly. Coming from the ‘Barun Goyot Formation’ shows that Avimimus lived in an arid environment
full of sand dunes and intermittent streams.
In the family, Caenagnathidae there were eleven genera with twelve species and two
specimens that are listed as ‘nomen dubium’. Caenagnathids had a temporal range
during the Late Cretaceous 91-65 mya. Distinct features were in possessing long
and shallow jaws (even the term: Caenagnathus,
the genus the family is named after, means ‘recent jaws’). Inside the lower
jaws bore a complex series of ridges and tooth-like processes, as well as a
pair of horizontal, shelf-like structures. The jaws as well were hollow being
air-filled, while supporting a fused dentary symphysis bearing distinct vascular
grooves. All, but the most basal caenagnathid possessed bony crests above the
skull. Caenagnathids were primarily herbivores, but most likely omnivores and
depending on which species, dieted on vegetation, invertebrates, eggs,
carcasses, small reptiles and young dinosaurs.
The presence of prominent notches (ulnar
papillae) on the ulna (bone of the forelimb) indicates the presence of long quilled
feathers on the arm. Ulnar papillae, or quill knobs are raised bumps or scars
on the ulna bone exhibiting where muscle or tendons were attached to articulate
feathering. In an Alberta, Canada fossil find of Apatoraptor (Ah-pat-o-rap-tur) the ulnar papillae are well
preserved. It gives evidence that this 74 mya Late Cretaceous caenagnathid and
its relatives could wave its short but strong feathered arms vigorously in
showing off for display.
Artist: Zhao Chuang Beibeilong nesting
Caenagnathids made ringed nests in the
earth and laid their eggs circular in fashion inside and on the edge of the
nest. Beibeilong (Bay-bay-long) with
a temporal range of ~ 93.9 mya in the Late Cretaceous is only known from a nest
of eggs and a fully developed embryo. After a careful phylogenetic analysis, it
was determined that the embryo was nested inside the family, Caenagnathidae belonging to a genus of
its own. The embryo was dubbed, ‘Baby Louie’.
Artist: Vladimir Rimbala ‘Baby Louie’ fossil
occurring 90 mya in the Late Cretaceous is so far the most primitive and
smallest caenagnathid at 0.61m/2ft long and did not possess a crest. The
relatively smooth beak bore a rounded and blunt tip, which is different than
other caenagnathids, but all caenagnathid beaks varied, showing an evolvement
to fulfill particular ecological niches. Although its fossils were found in
Asia, Caenagnathasia is more closely
related to the North American Campanian-Maastrichtian caenagnathids exhibiting
a migration from Asia into N. America.
Artist: Luis Rey Gigantoraptor fending
At 8m/26ft long and 5m/16ft tall, Gigantoraptor (Gee-gan-to-rap-tor) is
not only the largest caenagnathid; it is also the world’s largest known
feathered dinosaur. Living in the Late Cretaceous 85 mya, Gigantoraptor most likely had feathering as the other caenagnathids
did, but not as much due to size inducing gigantothermy, such as ostriches in
having bare skin on the hind limbs and neck. So feathering was decreased for
insulation, but some still remained for displaying and the brooding of eggs and
young. It hailed from what is now Mongolia.
The thighbone was relatively short with
the slender and elongated lower hind limb fibula and tibia bones supporting a
pes (foot) ending in three large and strongly curved toe claws. This suggests
that Gigantoraptor was an excellent
runner. The forelimbs ended in elongated slender hands. Digit I (thumb) of the
manus (hand) was short but strongly divergent. The frontal portion of the
caudal (tail) vertebrae possessed long neural spines and was heavily
pneumaticised with deep pleurocoels, while the middle section is somewhat
stiffened by long prezygapophyses (superior articular vertebra processes). The
caudal distal (end) was lightened with spongy bone. The jaws were toothless
ending in a horny beak with the lower jaws fused into a broad shovel-like
Artist: Esther van Hulsen Oviraptor beak
Having close relations to caenagnathids,
had a temporal range in the Late Cretaceous 84-66 mya. They were small with
most being between 1-2m/3.3-6.6ft long coming from Asia and in particular from
what is now, Mongolia in the Gobi Desert. As caenagnathid relatives, the jaws
were edentulous (no teeth), but instead, oviraptorids had two small bony
conical projections protruding from the roof of the mouth. Most likely, all
were herbivores as their beaks attest to an excellent tool for shearing
vegetation, but may have been also omnivorous. The jaws ended in a short horny
beak with the deep set mandibles possessing fenestrae (openings). The nostrils
were set high and far back from the snout tip. In the four genera, Oviraptor, Citipati, Banji and Rinchenia
and the recently found, Huanansaurus,
there was a prominent midline cranial crest. All told there are 18 genera, 18
species and one ‘nomen dubium’ specimen.
Artist: Julius T. Cstonyi Oviraptor nesting
Occurring 75 mya in the Late Cretaceous, Oviraptor (O-vee-rap-tur) is the oldest
oviraptorid and defines the family members as those most closely related to it.
At 2m/6.6ft long, due to fossilized nest sites of eggs, developed embryos,
hatchlings and adults, we know that Oviraptor
brooded nest contents and probably cared for the hatchlings and young. As in
all oviraptorids, feathering covered the entire body and in addition, Oviraptor possessed a set of rib
processes that kept the ribcage rigid, such as that found in extant birds.
Artist: Dennis Wilson Oviraptor near full term hatchling
Oviraptor was primarily
an herbivore, but supplemented its diet with animal protein as the remains of a
lizard were found in the gut area of an Oviraptor
fossil. Also, as its fossils have always been near at what were once bodies of
water, it may have strolled along shorelines and banks to locate mussels to
crack and pry open with its beak.
Artist: Nathane Rogers Khaan
Khaan’s (Kahn) temporal
range was during the Late Cretaceous ~ 75 mya with fossil remains coming
fromthe ‘Djadochta Formation’ of
Mongolia. At 1.1m/3.6ft, it lacked the expansion of the third metacarpal as
seen in other oviraptorids. Dieting on vegetation, it also supplemented its
diet on small vertebrates. It appears that Khaan
was sexually dimorphic. On some fossil specimens the caudal (tail) vertebrae
have reduced chevrons and this trait is analogized as a female feature in
increasing room for the laying of eggs. Chevrons are a series of bones on the
underside (ventral) of reptile tails protecting nerves and blood vessels. Khaan was crestless.
Artist: Zhao Chuang Huanansaurus
Huanansaurus skull fossil
Another oviraptorid is in the 2015
recently discovered Chinese fossil of, Huanansaurus
(Hah-nan-sawr-us). Found during the construction of a railroad station in
Jiangxi, Province, it had a temporal range in the Late Cretaceous 72 mya. At
24cm/9.5in long, Huanansaurus had
some distinct features in the quadrate bone’s lower condyles being positioned
behind the upper head. As crested, on the roof of the skull’s rear, the
transverse nuchal crest wasn’t as prominent as in the front. The mandible
(lower jawbones) is angular in form making up an outer side opening in the
lower rim. In having a concave rim, the dentary (anterior bone of the lower jaw)
covers the outer side opening of the lower jaw. The dentary bone is highly
Artist: Ville Sinkkonen Banji
The last oviraptorid to be discussed
here is the most derived in, Banji (Ban-gee)
that lived 66 mya at the end of the Late Cretaceous in what is now Jiangxi
Province, China from the ‘Nanxiong Formation’. Being a juvenile and not fully
grown, the fossil is only 65cm/26in long. However, the adults would not have
been much larger. Compared to other oviraptorids, the nasal cavity is unusually
large that followed the crest’s curve almost to the eye orbit (socket). It was
a crested oviraptorid which was formed by the nasal bones and premaxillae with
the sides sporting a series of vertical striations along the sides. The crest
ended in a stepwise caudal bearing two longitudinal grooves. Lightly built, it
is thought as other oviraptorids that Banji
was primarily an herbivore, but would also have chased down small
Paraves (Purr-aves) ~
With a temporal range from the Middle Jurassic to the present 165-0 mya, the
ancestral paravian is the earliest common ancestor to birds and its stem
lineage is more related to birds than to the oviraptorosaurs. We usually think
of dinosaurs as gargantuan, but instead of enlarging, paravian ancestors
started shrinking in size 200 mya in the Early Jurassic. In this evolving
miniaturization, paravians also evolved new adaptations four times faster than
other dinosaur groups. One case of this paravian paedomorphism is in progenesis
where sexual development is accelerated. The exceptions though are in the
dromaeosaurids and troodontids where the former went through three independent
stages towards gigantism, while the latter, the troodontids went through one.
This major clade is the crown group to
modern birds, but as branch based there are no extant species or genetic
material from their descendancy into their avian ascendants, even though all members
of Paraves are a direct lineage to
birds. Like the theropods before them they were bipeds with most walking on
three toes. The basal or, earliest paravians, like the dromaeosaurids and
troodontids developed a hyperextended ligament that held digit II (second toe)
well above the ground, forcing them to bear weight on just digits III and IV.
Digit II distally ended in a sickle shaped claw that became a formidable weapon
and tool in hooking to gouge, but not necessarily in slicing. As weakly keeled
on its underside, the claw was used more for climbing by puncturing and
gripping. The climbing could have been performed on an object like a leaning
tree trunk or on a large prey while they were hunting in packs. For smaller
prey it would have been used for pinning it down as extant raptors do today.
Artist: Emily Willoughby Balaurbondoc
The highly modified hallux (digit I or,
first toe) became fully reversed in paravians. Of the paravian belonging to the
Avialae clade that will be discussed
later, Balaurbondoc (Bah-la-wur = bon-doc) took the hind limb’s digit I to a
whole new level by having digit Irun
parallel to digit II. Its digits I and II were held as retracted bearing
enlarged sickle-shaped claws on each digit.
All paravians were covered in feathers
and in most cases the legs and feet were covered. They were the first to evolve
true wings and in some forms...flight. In the most basal, the wings usually
bore three large flexible fingers ending in claws, while in later more derived
forms, the fingers became fused stiffening the forelimbs which is the case for
all modern birds. Also, as borrowed from the earliest of coelurosaur ancestors,
an increasingly asymmetric wrist joint evolved that modern birds would inherit
as well. The importance to this wrist was that it allowed for a strong
musculature flapping of the wings and along with the forelimb elongation,
eventually led to flight.
Artist: delirio88 Microraptor in flight
Flight developed independently among the
paravian groups with one of the earliest in being, Microraptor (My-crow-rap-tur). Analysis from extensive anatomical
studies proved that Microraptor was
capable of powered launching and flapping flight. But for most species, free
flight was not obtained and were either flightless or gliders from heights to
Paraves is divided up
into two basal paravian families and one clade. The two families are Anchiornithidae (An-kee-or-nith-ah-day)
and Scansoriopterygidae (San-soh-ree-op-tuh-rig-uh-day)
while the clade is, Eumaniraptora
(U-man-ee-rap-tor-uh). In the family, Anchiornithidae
there are currently ten genera and in, Scansoriopterygidae
there are at present three genera. Eumaniraptora
includes the order, Deinonychosauria
(Die-non-ih-ko-sawr-ree-ah) that consists of the two families, Dromaesauridae Dro-mee-o-sawr-ah-day and
Troodontidae (Troh-o-don-tuh-day). As
a eumaniraptoran sister clade to deinonychosaurians, Avialae (A-vee-l-ee) is in the direct line of dinosaurs to what we
Anchiornithids had a temporal range of
165-122 mya in the Late Jurassic-Early Cretaceous and due to their phylogenetic
taxonomy might just very well be the most basal family of the bird line, even
though none could fly. Fossil finds have mainly been found in China’s Late
Jurassic deposits, although Yixianosaurus
(Yi-chow-o- sawr-us) was found in China’s Early Cretaceous ‘Yixian Formation’
and Ostromia’s (Oss-trom-ee-uh) remains
were discovered in Germany’s Late Jurassic Bavarian deposits attesting to a
rapid Laurasian dispersal of eumaniraptorans.
Sharing features of other paravian
groups, the more derived eumaniraptorans and basal avialans, anchiornithids
were a transitional group in leading to birds. In fact, the term, Anchiornithidae refers to ‘near birds’.
Anchiornithids are known for their long forearms, hind limbs and hands. They
were lightly built, small and fully feathered. With much variety in feathering
between genera, it is certain they possessed pennaceous feathers, although it
is uncertain if the feathering possessed barbules on the forelimbs making them
unspecialized for flight. Most had pennaceous feathers also running down the
legs giving this eumaniraptoran family the dubbed moniker, “four-winged
dinosaur.” Most had a feather vaned tail.
As in some avialans, the inside surface
of the acromion margin (a bony process on the scapula) is bent hooking
outwards. The small anterior dentary (mandible) teeth are more numerous and
spaced closer together than the teeth in the middle of the tooth row, much like
their eumaniraptoran cousins the troodontids. As in alvarezsaurids,
therizinosaurids and avialan species, the inside surface of the fibula’s
proximal part is flat.
A genus of Anchiornithidae is, Serikornis
(Say-ree-kor-niss) that lived ~ 161-160 mya during the Middle Jurassic in what
is now China in the ‘Tiaojishan Formation’. Serikornis
had more than one feather type composed of short and symmetrical vaned forelimb
feathers with both fuzz and long pennaceous feathers on the hind limbs. The
tail is covered proximally by filaments and distally by fine rectrices (larger
tail feathers). While the neck was covered in wispy feather bundles, the body
possessed a pennaceous-like feather covering.
Although Serikornis was ‘four-winged’, its skeletal anatomy and the complete
absence of barbules on the feathers, the microstructure allowing feathers to
resist air pressure during flight, attest it could not fly. However, it
assuredly had the ability to flap its wings to increase hopping height and from
a higher elevation had the capability to glide down.
A main distinguishing feature of Serikornis is in its dentition, which
are small when thinking dinosaur teeth, but the anterior maxillary teeth were
larger than any other anchiornithid. From luminography scans, the cervical
vertebrae showed small pneumatic cavities. This 60cm/23.6in long basal anchiornithids
was most likely an insectivore and carnivore in dieting on large insects and very
Another anchiornithid was Eosinopteryx (E-oh-sigh-nop-tur-ix)
which lived during the Middle Jurassic 160 mya. The virtually complete
articulated fossil remains were also, as Serikornis’
remains, found in China’s ‘Tiaojishan Formation’. The holotype fossil is of a
nearly fully grown subadult measuring 20cm/12in long. The adult would not be
much larger, if at all, than that.
Artist: Emily Willoughby Eosinopteryx
Fully feathered, if Eosinopteryx were alive today and if spotted by most anyone, they
would say it was a bird, but they would be wrong, for it was very much a non-avian
dinosaur. It however lacked the fully developed tail feathering that would have
allowed for steering, so it would’ve been rudderless during flight. The wing’s
primary feathering was twice as long as the humerus (upper arm bone) in which
the arm structure was not designed for flapping. The hind limbs’ lower tarsals
were featherless. The feet and toes were very slender and distally lacked any
curved claws for defense, predation or climbing. However, the straight pedal
claws would have allowed for swift cursorial terrestrial running.
The skeletal anatomy, which lacks a
keel, is much like troodontids and so much so, it was originally classed as
one. But numerous features such as a very short snout, a short tail and an
unusual arrangement of wing bones placed it as an anchiornithid. With its
dentition of unserrated, but sharp teeth, Eosinopteryx
could have easily chased down and seized struggling insects and small
vertebrates while crunching them in the mouth.
Artist Zhao Chuang Caihong
There has been a new anchiornithid just
described this year (2018) that was first discovered by a Chinese peasant in a
quarry near the small village, Nanshimenzi and handed over to scientists in
2014. The new anchiornithids is, Caihong
(Kay-hong) which literally translates in Chinese to, ‘rainbow’ and for good
reason. A microscopic evaluation of the body, tail, neck and head feathering
impressions revealed melanosome nanostructures that are similar to organelles
that produce iridescence in extant birds. In addition, the feathers found on
the head, chest, and the base of the tail preserve flattened sheets of
platelet-like melanosomes very similar in shape to those which create brightly
colored iridescent hues in the feathers of modern hummingbirds. These feather
structures however, appear as solid lacking the air bubbles as seen in
hummingbirds today, yet the feathering of Caihong
represents the oldest known evidence of platelet-like melanosomes.
Caihung fossil feathering
Caihong at 40cm/16in
long had a temporal range in the Late Jurassic 161 mya. Like other
anchiornithids, it had a prominent lacrimal (small bone forming part of the eye
socket) crest and possessed longer pennaceous feathering on the forelimbs and
hind limbs and displayed large asymmetrical tail feathers. The recurved
premaxilla teeth are more slender and tightly packed than the other teeth. The
large hind limbs were 3.1 times longer than the torso. Ending in a hook-shaped
foot, the pubic bone slightly directs toward the rear.
Caihong skull fossil
One more anchiornithid we’ll mention
here, is the most basal paravian yet in, Yixianosaurus
(Yi-chow-o-sawr-us). With an Early Cretaceous temporal range of 122 mya, the
fossil remains come from the ‘Yixian Formation’ of northeastern China. With a
feature known only among paravians, the mediolateral width of the humerus is
much greater than the width of the scapular blade in Yixianosaurus. The lateral process of the ulna is sub-equal to the coronoid
process in size, which is also a typical paravian trait. The manus (hands) and
metacarpals (finger bones) are 140% longer than the length of the humerus
(upper arm long bone). Digit II (second finger is the longest) but all three
fingers supported bored large recurved claws. The long hands and short arms
probably evolved independently within this genus. The large hands and curved
claws most likely aided in capturing prey of small vertebrates and used in
defense. At ~ 1m/3.3ft long, Yixianosaurus
sported large pennaceous feathering on the forelimbs and arm anatomy, these
features could have supported limited aerial locomotion.
Artist: Masato Hattori Yixianosaurus
Scansoriopterygidae is a family
consisting of three paravian genera that arose 165-156 mya in the Middle to
Late Jurassic. All genera come from the ‘Tiaojishan Formation’ fossil beds of
China. The family contains members that were the first non-avian dinosaurs that
had adaptations to an arboreal (tree dwelling) lifestyle, including climbing
and gliding. No more the size of a pigeon reaching maximum lengths of
16cm/6.3in long, scansoriopterygids were the smallest of all non-avian
Artist:Román García Mora Scansoriopterygid fishing grubs
Scansoriopterygids had an extremely long
third finger which was in contrast to other dinosaur groups that had a longer
extended second finger, as in Yixianosaurus
described just above. The elongated digit most likely aided in climbing as the
term, scansoriopterygid refers to ‘climbing wings’ and fishing out grubs and
adult insects from trees and bark, much like the extant aye-aye does today.
The scansoriopterygid skull is blunted
making the snout short-faced while the anterior end of the lower jaw is
slightly downturned and the teeth are procumbent. This skull shape
superficially is similar to some insectivorous bats and is quite similar to
that of early oviraptorosaurs, like Caudipteryx.
Scansoriopterygids’ paleoecology during
the Middle-Late Jurassic consisted of a warm and humid climate supporting
gymnosperm, ginkgopsid and coniferous trees, while other semitropical plants
like lycopsids, horsetails and cycads abounded giving scansoriopterygids places
to scamper, climb and hide and dine in as the ecology supported large insects,
other invertebrates and small vertebrae populations.
Artist: Matt Martyniuk Scansoriopteryx
With a temporal range in the Early to
Late Jurassic 165-156 mya, Scansoriopteryx
was ~ 35cm/13.8in long as an adult. The fossil remains of a hatchling at
13.5cm/5.3in long and a juvenile at 16.5cm/6.5in long holotype fossil were
found in China from the fossil beds of the ‘Tiaojishan Formation’.
Scansoriopteryx (formerly known
as, Epidendrosaurus) had a more opened non-perforated hip socket than most
other dinosaurs where the pubis pointed backwards and downwards. Small pebbly
scales were preserved in the fossil finds on the metatarsus (upper foot) where
the foot ended in a large hallux (first toe). Also notable in the fossils is
the wide rounded jaws with twelve teeth in the lower jaws that were larger in
the front of the mouth than in the back. The long tail was 6.5 times the length
of the femur.
Scansoriopteryx skeletal (Note long fingers)
The most notable features in Scansoriopteryx were the long fingers,
in particular the third one. These forelimb distal digits give evidence of an
arboreal lifestyle and they were fairly developed even at an early age as
viewed in the hatchling fossil. This scansoriopterygid’s body possessed both
downy and larger feathers.
Just to let ya know, with a slew of
initial confusion in its naming, original provenance, taxon placement and
whether it should be called a dinosaur versus a bird, the storm appears to have
abated as it is now comfortably nestled in the family, Scansoriopterygidae which was named after this tiny dinosaur we
Artist: Pablo Lara Epidexipteryx
was a small scansoriopterygid that lived in the Late Jurassic 160 mya in the
‘Dauhugou Beds’ of what is now Inner Mongolia. It was around the size of a
pigeon at 44.5cm/17.5in long including the tail. The retrices’ (tail feathers) four
long vanes weren’t branched into individual filaments as extant birds are, but
were made up of a single ribbon-like sheath. The body was covered in more
primitive dinosaur feathering, but also some feathers arose from a membranous
base like modern birds do and may be the beginnings in the evolution of the
bird feather and its anchoring.
Resembling oviraptorosaurs skulls, the
skull of Epidexipteryx had some
unique features. It only had teeth in front of the jaw that angled outwards
instead of downwards and the lower jaw curved down and away from the upper jaw.
This arrangement made the lower teeth point outwards instead up into the upper
jaw. Also, Epidexipteryx lacked
remiges (wing feathers) but may have had a membrane supported by the forelimbs
Epidexipteryx skeletal anatomy
Although the skeletal anatomy of Epidexipteryx proves a close relation to
Scansoriopteryx, there is contention
that it’s ancestral to oviraptorosaurs.
The third member of scansoriopterygids
I’m not going to use the genus name only in describing it, but am going to also
use its specific epithet in giving the binomial species name. The reason for
doing so is while we are used to long winded species names, this
scansoriopterygid has only four letters and is tied with a bat species for the
shortest species nomenclature. The genus is merely, Yi, while the specific name is simply, qi. So, there ya have it, we’ll be describing this little guy by it
species name of, Yiqi (Yee-chee).
In speaking of the bat species name of, Iaio,
Yiqi gave the impressionable appearance of a bat straight out from
the bowels Hades. This scansoriopterygid with a temporal range during the Late
Jurassic 160 mya had a bony rod called a ‘styliform element’ jutting backward from
each wrist that, along with the elongated fingers supported a patagium (skin
membrane) reminiscent of a bat wing.
Artist: Emily Willoughby Yi qi
Unique to Yiqi from all other
dinosaurs was in possessing a plane of skin membrane between each finger as
evidenced from wrinkled skin in between each finger of the fossil. Extant birds
of flight do have a short membrane called a propatagium, but Tiqi’s
membrane expanded more like a bat’s patagium. Whether it flew or glided, the
mechanics of the forelimb are still under study, but most likely it used its
wings for gliding as extant gliders, like flying squirrels and the greater PetauroidesVolans both have styliform elements for membrane support.
In addition, the head was short with a
blunt snout and a downturned lower jaw that held teeth angled forward. With
four on each side, the larger upper front teeth pointed slightly forward. There
were no other teeth except for those in the front tip of the mouth much like
its scansoriopterygid relative, Epidexipteryx.
Approximately 32cm/12.6in long, Yiqi’s
body, from the base of the snout to the caudal (tail) was covered in
paintbrush-like quilled feathers. Only the tip of the snout, the patagium,
ankles and feet had no feathering, although the bottom leg covering was long
enough to layer over the top half of the foot’s metatarsus. Behind the shins
and long slender forelimbs sported Yiqi’s longest feathers although the
patagium lacked any feathering cover.
Below is a short video clip put out by
Nature about Yiqi:
As the sister clade to Oviraptorsauria, Eumaniraptora is composed of members having a temporal range from
the Middle Jurassic to the present 165-0 mya. The two eumaniraptoran subgroups
are Deinonychosauria (Die-non-ih-ko-sawr-e-uh)
and Avialae (A-vee-ale-e). There was
a global distribution of eumaniraptorans with fossil finds showing up on all
continents within diverse environments. Under the avialan line eumaniraptorans
are the only dinosaur group to evolve flight eventually leading to dinosaurs
called birds. Depending on species, the diets are highly varied in the forms of
carnivores, insectivores, piscivores, omnivores, frugivores and
herbivores.Eumaniraptorans are the last
remaining theropod group and all other dinosaur groups to survive the K-T
All eumaniraptorans strictly have an
obligate bipedal gait with a distally placed metatarsal forcing pedal (foot)
digit I to touch ground or wrap around objects like branches. The claws were
sickle-shaped, while pedal digit II was retractable on the more primitive
deinonychosaurians. These theropods were small overall in body size with long
slender limbs and proportionately long hands. They all were bird hipped with a
backward facing pubis and also had long leg, arm and tail feathers. The tail
itself was mobile at the base and stiffened the rest of the length. The limbs
had long feathering and the more derived had conquered limited free flight.
Deinonychosauria: The more basal
group of eumaniraptorans is from the order, Deinonychosauria
that had a temporal range from the Early to Late Cretaceous 143-66 mya. The
name is derived from Greek inferring ‘terrible claw’ in reference to the
retractable sickle-shaped claw found distally on pedal digit II. Most fossil
finds have been discovered in Asia and N. America, although there have been
fragmentary remains discovered in northern Africa. These are all, based on
Gondwana diversity, but with two finds of dromaeosaurid fossils in what is now
Argentina’s Patagonia region during the Late Cretaceous of, Neuquenraptor (90 mya) and Unenlagia (~89 mya), bears out that
worldwide distribution of deinonychosaurians was well underway at least by the
beginning of the Cretaceous and before the breakup and drifting apart of the
northern (Gondwana) and southern (Laurasia) hemispheres. During the Jurassic,
there was greater connection between the two hemispheres allowing for
dromaeosaurid migrations further evidenced by scant European fossil finds
including the dromaeosaurid trademark pedal digit II sickle-shaped retractable
claw. Again, Deinonychosauria is
divided into Dromaeosauridae (Dro-me-o-sawr-us)
and Troodontidae (Tru-o-don-tee-day.)
are the most basal of the deinonychosaurians that have an Early to Late
Cretaceous temporal range of 130-66 mya. Most were small, but a few were over
5m/16.4ft. The smallest is the microraptorian, Hesperonychus (Hes-purr-uh-nie-kus) at 50cm/19.7in, while Achillobator (Ah-kill-o-bay-tur) was the
longest at 6m/19.7ft long. The miniaturization in size is a feathered
dinosaur’s hallmark trait towards the path to the origins of bird flight.
Dromaeosaurids are quite extensive with
the Dromaeosauridae clade’s taxa
containing three subfamilies and one subgroup node order with three subfamilies
of its own. Thus far, altogether, there are at least 43 genera, which don’t
include suspect dromaeosaurid scant or extensively disarticulated fossils.
Dromaeosaurid caudal (tail) vertebrae
were tightly locked, much more so than in other theropod groups. In fact with
the microraptorians and eudromaeosaurs, chevron and neural arch extensions grew
extremely long turning the tail into a unique and effective stabilizer. As the
more basal dromaeosaurids had elongate metatarsi displaying a primitive form of
the arctometatarsalian condition in which the proximal part of the middle
metatarsal is pinched between the surrounding metatarsals, the more derived had
developed short and stout metatarsi. The arctometatarsus aided in speed but not
so much in agility. With the dromaeosaurid metatarsal and stiffened long tail
transition, it looks as if they opted out speed for agility. Still able to run,
just not as fast as their predecessors, the latter dromaeosaurids could now
commit quick agile turns in pursuing prey or evading predators.
Source: Encyclopedia Britannica Dromaeosaurid sickle claw
The sickle-shaped and retractable large
claw was held off the ground and used as a killing implement. When muscles of
the toe (digit II) were contracted, the claw swept downwards slashing and
impaling whatever animal was the dromaeosaurid’s intended victim. The claw
mechanics were backed by a claw base to tip angled momentum maximizing the
transmission of forces from the leg to the tip of the claw. With the second toe
held up, dromaeosaurids walked only with two weight bearing toes. All
dromaeosaurids were carnivorous and aided by excellent eyesight, as witnessed
by the size of their skull’s orbits and scleral rings, were cathemeral in being
active both night and day.
There are nine dromaeosaurid genera taxa
that are holotype dromaeosaurids and do not belong to any other subgroupings. Primarily
from Europe, out of these nine, there are at least five fossil finds that are
definitively dromaeosaurids, but further classification is difficult due to
current scant remains. They are: Nuthetes
(New-thet-eez) from England 143 mya, Ornithodesmus
(Or-nith-o-dez-mus) from the Isle of Wight 125 mya, Variraptor (Var-e-rap-tor) from France 70mya, Pyroraptor (Pi-row-rap-tor) from southern France 70.6 mya and Adasaurus (Aye-dah-sawr-us) from
Mongolia 70 mya. The remaining four genera are basal dromaeosaurids and are: Shanag (Shan-ag) from Mongolia 130 mya, Zhenyuanglong (Zen-yu-an-long) from
China 125 mya, Pamparaptor
(Pam-pa-rap-tor) from Patagonia, Argentina 89 mya and Luanchuanraptor (Loo-an-choo-an-rap-tor) from China ~77.5 mya.
Jonathan Kuo Pyroraptor
On a couple of light notes, Pyroraptor wasn’t named so because it
breathed fire like a dragon, no, it’s not that colorful; it was named due to
the fact that when a fire swept through a French forest, it uncovered the
fossil remains. Also, the term ‘raptor’ for theropods refers to dromaeosaurids
due to their shared characteristics in the Digit II (second toe) sickle claw,
grasping three-fingered manus (hands) and relatively large brain sizes.
However, not too many scientists like referencing the term ‘raptor’, preferring
instead the term dromaeosaurids as today’s birds of prey are considered
While speaking of dragons, Zhenyuanglong literally means,
‘Zhenyuan’s dragon’ in reference to the man, Zhenyuang Sun who secured the
fossil for study from a local farmer who found it in the ‘Yixian Formation’ of
Liaoning, China. At 1.7m/5.6ft, it was a medium sized dromaeosaurid. For a
dromaeosaurid it had short forelimbs that supported long well developed
pennaceous feathers while the body was coated with simple ‘hairy’ feathered
filaments. In fact, the short limbs were the shortest dromaeosaurid forelimbs
once an arm to leg ratio was conducted. Along the length of the tail, long
vaned feathering was evident while the fossil gives no evidence of long leg
feathering as the forelimbs possessed; something unusual as all other
dromaeosaurids with long arm feathers also had long leg feathering.
Artist: Chuang Zhao Zhenyuangalong
With all this feathering, Zhenyuangalong still couldn’t fly as
there were no strong muscle attachment scars that could’ve afforded flapping
wings. Also, its estimated weight of 20kg/44lb, for its size, it would’ve even
been too heavy to even glide. But, its weight and length makes it the largest
non-avian dinosaur with full blown bird-like feathered wings. The feathered
forearms were most likely used for display in threatening rivals and impressing
~ is the most basal subfamily of dromaeosaurids and through phylogenetic
analysis contains three Late Cretaceous genera, which are: Mahakala (Ma-ha-kah-la) from ~ 80 mya, Halszkaraptor (Houz-kuh-rap-tor) from 75-71 mya and Hulsanpes (Hul-san-pees) from 70 mya.
All halszkaraptorines came from Mongolia with a paleoecology consisting of a
semiarid climate, extensive sand dunes, alluvial settings and steppes
interspersed with intermittent streams. Where the more permanent bodies of
water were is also where halszkaraptorine fossils have been found. They were
attracted to the waters in a harsh dry climate and in doing so, Halszkaraptor evolved into a semiaquatic
Artist: Frank Ipollito Mahakala
Mahakala was the most
primitive of the primitive halszkaraptorines. At 70cm/28in long, Mahakala was not in the direct line of
avian dinosaurs, but shows that basal feathered dinosaurs were downsizing to
quickly find food and shelter. With its wing-like forelimbs and biped hind
limbs, it gives a consensus portrayal of the dinosaur’s ancestral lineage in leading
up to their final descendants…birds.
Although the ilium, ulna femur and tail
vertebrae were primitive in Mahakala and unlike most other dromaeosaurids its middle metatarsal was not pinched, as well as possessing short forelimbs, it still possessed the dromaeosaurid expanded
claw on digit II. It also had a combination of shared characteristics among
other dromaeosaurids, troodontid members and birds.
Credit: St. Thomas Pro. Halzkaraptor
With a long neck, a goose-like beak and postural
adaptations similar to short-tailed aquatic fowl, Halszkaraptor looked a lot like a swan. In addition, Halszkaraptor possessed eleven sharp
needle-like teeth in a flattened premaxillae, did not
possess the typical dinosaurian epiophyses (bony projections of the cervical
vertebrae) in which the cervical (neck) vertebrae had reduced neural spines, external nostrils were situated behind the premaxillae but in front of the
maxillae and digit III of the forelimb was longer than digit II.
At 60cm/23.6in long, Halszkaraptor, as mentioned earlier due
to the arid conditions it and the other halszkaraptorines lived in, it not only
lived near bodies of water, it lived in them evolving into a semiaquatic
lifestyle. Through synchrotron radiation scans, the intricate inner ear was
visible and evidence of snout nerve channels, like in crocodiles, were found
that gave heightened sensitivity to touch. Along with the elongated neck, this
afforded Halszkaraptor to snag small
fish prey as it swam with the head underwater seeking out fish with its
sensitive snout. With the forelimbs used as paddles and slightly webbed hands while the long tail shifted its center of gravity forward, it swam through
water with ease.
Halszkaraptor, as a biped
could easily run, maneuver with ease using the long tail for stability and dwell on land
as well for nesting and hunting small vertebrates and large insects in
utilizing its sharp claws.
~ is a subgroup clade of ancestral Gondwanan dromaeosaurid theropods with
remains being found in South America and Antarctica. Unenlagiines have a
distinct anatomy from the Laurasian dromaeosaurids which was consequential from
Pangaea’s breakup into Gondwana and Laurasia resulting in isolating
unenlagiines from the rest of the dromaeosaurid family members. This initiated
separate evolutionary paths. The temporal range is 94 -70 mya during the Late
Cretaceous when the tip of S. America and Antarctica were connected.
Unenlagiines possessed the typical
dromaeosaurid extended and sickle-shaped claws, but distinguished by even
lengthier chevrons and superior processes in caudal (tail) stiffening and a
posteriorly oriented pubis. Although they were showing dental (teeth) reduction
as other dromaeosaurid groups were, they still retained a higher dental count.
The small size of the teeth was pronounced when compared to skull height, while
in addition, unenlagiines possessed longitudinal grooves on the tooth crowns.
There are a total of six unenlagiine genera,
although it has been pretty much in agreement that Rahonavis (Ray-ho-nay-viss), due to its morphology is going to be
reclassified under Avialae as being
closer to birds. Rahonavis displays
both dromaeosaurid and avian dinosaurian features, in which these transitional
features make for much difficulty in where it should be classified. The
temporal range for this subgroup is from the Late Cretaceous 94-70 mya.
The other five unenlagiines are: Buitreraptor (Bwee-tree-rap-tor) from 94
mya, Neuguenraptor (Nu-kin-rap-tor)
from 90 mya, Unenlagia
(U-nen-lag-ee-ah) from ~89 mya, Unquillosaurus
(Un-key-o-sawr-us) from 75 mya and
Austroraptor (Aw-stro-rap-tor) from 70 mya. Unenlagiines are known for
their low hanging and long heads and smaller conical teeth when compared to the
northern hemisphere dromaeosaurids’.
Artist: Joshua N. Edder Buitreraptor
Buitreraptor, at only1.5m/4.9ft
in total length (excluding Rahonavis
at 70cm/27.6in) was one of the smaller dromaeosaurids and smallest of the unenlagiines.
With its fossil remains coming from what is now, Patagonia, Argentina, Buitreraptor is the most basal
It had a rather long slender snout most
likely to poke into crevices and holes to either snag or scare out small
reptiles and mammals from their hiding places. It most likely also waded along shorelines
to snatch small fish and aquatic vertebrates. The snout was filled with tiny
unserrated teeth that were grooved, flattened and strongly recurved in
structure, perfect for seizing struggling and slippery small prey.
Buitreraptor skeletal anatomy
Buitreraptor’s remains show
a mosaic of anatomical features when compared to other dromaeosaurids,
troodontids and even the more advanced avialans. But, it was more primitively
distinctive with shorter fingers that were essentially the same length. It did
possess the sickle claw on the second toe and was most likely, due to its
smaller size was used to pin down prey rather than utilizing it to kill prey as
the other larger dromaeosaurids did.
Artist: Fred Wierum Austroraptor
At 5-6m/16.4-19.7ft, Austroraptor (Aw-stro-rap-tor) was one
of the, if not largest dromaeosaurid, but for sure is the largest dromaeosaurid
found in the southern hemisphere; Austroraptor
may even have reached a length of 6.5m/21ft. Its fossil remains were found
in rocks of the ‘Allen Formation’ from the far southern region of Argentina in the
Río Negro Province. It must have subsisted on larger prey as the juvenile
sauropods, Rocasaurus and Saltasaurus that shared the same
paleoenvironment, would have been accessible for this predator.
Like all unenlagiines, it had small
non-serrated conical teeth. The descending process of the lacrimal (bone
situated on front part of eye orbit’s medial wall) curves anteriorly. Several
skull bones resemble features of Deinonychus,
a troodontid, but the forelimbs were distinctive to other dromaeosaurids in
being shorter proportionately to the rest of the body with the humerus being
half the length of the leg’s femur. The small humerus might be due to Austroraptor’s size increase, as most
theropods did lose forearm length while increasing body size.
~ is a subfamily clade of basal dromaeosaurids with an Early to Late Cretaceous
temporal range of 125-76.5 mya. Microraptoria,
as an order is frequently found in literature as synonymous to Microraptorinae. Microraptorines, or as
ya like, microraptorians first appeared in what is now China and the specific
region of the ‘Yixian and Jifuotang Formations’ of Liaoning County, China is
where they all came from. The only exception to this is, Hesperonychus, in which its fossil remains were found in the
‘Dinosaur Park Formation’ of Alberta, Canada.
Microraptorines were some of the
smallest dinosaurs with the three species in the genus Microraptor reaching lengths of only .77-.9m/2.53-2.95ft. The limbs
were slim and long with all four limbs and the tail supporting advanced
feathering on some species positing them in the ‘four-winged’ dinosaurs. The
largest ‘four-winged’ dinosaur since found is the microraptorine, Changyuraptor that reached 1.2m/3.9ft in
Artist: Qilong Genus Microraptor
Microraptorine distinctive dromaeosaurid
characteristics are: a maxilla laterally sculpted by small pits, very short
manual phalanx III-2, shortened first digit of the hand, splatulate (rounded)
pubic symphysis, metatarsal III with a pinched proximal end and a slender
It is not known if microraptorines were
capable of free flight, but due to anatomical features and morphology as
evidenced from extremely well preserved fossils, there certainly is good
argument they could glide. One thing that we do know though is that Microraptor, from 120 mya during the
Early Cretaceous, not only had feathering, it also had iridescent plumage.
Artist: Jason Brougham Microraptor gui
Comparing the feather melanosome (melanin
containing organelles) remains of Microraptor
to those of modern birds with iridescent feathers shows that M. gui’s feathers were black and
iridescent in color and structure. From camouflage, thermoregulation, signaling
(mating, competition) and to flight, feather colors have played main roles that
birds picked up from their dinosaur ancestries.
M. gui Fossil with iridescent feathering
Below is a short video of Microraptor’s iridescent plumage:
Tianyuraptor was the most
primitive microraptorine and did not possess these typical microraptorine
traits: a large oval fenestra in the coracoid, significantly shortened
penultimate manual phalanges, the posterior end of the ilium extending ventral
to the ischial peduncle, lateral projections halfway down the pubis and a
strongly anteriorly curved pubic shaft.
Within the microraptorine subgroup are
seven genera with three species in Microraptor
while the rest only have one species in each. The genera are: Graciliraptor (Gray-sil-e-rap-tor) of
126 mya, Changyuraptor
(Chang-you-rap-tor) of 125 mya,Zhongjianosaurus between 125-120
(Sign-or-nith-o-sawr-us) between 124.6-122 mya, Tianyuraptor (Tee-an-you-rap-tor) of 122 mya, Microraptor (My-crow-rap-tor) of 120 mya and Hesperonychus (Hess-puh-ruh-nye-cuss of 76.5 mya.
Artist: Midiaou Diallo Zhongjianosaurus
Zhongjianosaurus, at 70cm/28in
is the smallest of the dromaeosaurids and thus far the smallest of the
non-avian dinosaurs. In sharing dromaeosaurid traits, it is distinguishable
with proportionally long ossified uncinated processes fused to the dorsal ribs.
It also had a widely arched furcula with slender and posteriorly curved
clavicular rami. The humeral proximal end was strongly offset medially from the
humeral shaft and the internal tuberosity of the humeral proximal end was
short. A large fenestra perforates the humeral deltopectoral crest, while the
humeral ulnar condyle was hypertrophied.
size suggests that there was during its time, a sufficient amount of niche
partitioning. Possibly being omnivorous and arboreal, niche partitioning may
have aided in preferential habitat differences.
As a dromaeosaurid, Sinornithosaurus had the typical sickle-shaped toe claw and was a
close relative to the microraptors. It possessed two types of feathers with one
being formed as tufts from several filaments joining together, while the second
type as exhibited on the forelimbs, legs and tail were composed of rows of
filament joined together along the main shaft (rachis) much like modern birds.
Although it couldn’t perform free flight, it could glide short distances after
jumping from trees. Microscopic cell structure studies of the feather fossil
remains show a variance in body color of reddish-brown, yellow, black and
Artist: AMHR R. Mickens Sinornithosaurus
However, what makes Sinornithosaurus so distinct is that it may have been able to
deliver a venomous bite. Just as rear-fanged snakes and gila monsters, Sinornithosaurus had upper rear-fangs
that were grooved and just like these other reptiles, it appears that Sinornithosaurus had a venom gland just
above the back of the jaw connected to the grooved teeth via a canal.
Rear-fanged snakes and gila monsters must bite then chew to allow the venom to
flow into the wound. It is thought by the initial paleontologists who studied
and evaluated the Sinornithosaurus
fossils that it also did the same thing.
There is a group of paleontologist that
are now disputing this in saying there were other dinosaur teeth with grooves,
so it doesn’t prove that Sinornithosaurus
had the capability to deliver venom. But with the assemblage of the grooved
teeth, the cavity where the venom gland could’ve been placed and the tube-like
canal connecting the two, it certainly seems reasonable that Sinornithosaurus through convergent evolution
could have developed a venomous delivery system. Below is a BBC video of Sinornithosaurus and in it, the video
explains the venom assembly. So you be the judge in whether there was a
dinosaur that had a venomous bite.
Hesperonychus is the only N.
American microraptorine thus far discovered and as mentioned earlier, was found
in Alberta, Canada. Its name means, ‘western claw’. It was small measuring ~
60cm/23.6in in total length. Even though it was a miniature dinosaur, it was
well equipped with dagger-like teeth and razor-sharp claws with the distinctive
dromaeosaurid sickle claw on the second toes of each foot. Most likely it was
chiefly an insectivore supplementing the diet on terrestrial invertebrates,
small mammals and quite possibly on occasion a carcass whenever it came across
Credit: Alchetron.com Hesperonychus
The pubic bones of Hesperonychus were fused with the rest of the skeletal anatomy made
up of gracile bones. The pubic symphysis as a cartilaginous joint was spatulate
or rounded. In being small, it played an important role in the ecosystem it
lived in by infusing the predator/prey relationship within smaller animals.
next main subgroup of dromaeosaurids is in the class node of, Eudromaeosauria (U-dro-me-o-sawr-e-uh)
with the meaning of ‘true dromaeosaur’. With a temporal range of 143-66 mya
ago, eudromaeosaurines are the most derived of dromaeosaurids, were large
bodied as compared to other dromaeosaurid groups and were feathered
hypercarnivores with a diet consisting almost entirely of vertebrate flesh.
Eudromaeosaurines filled ecological niches as small carnivores and piscivores.
All eudromaeosaurines possessed an
expanded and large heel jutting from the second phalange (toe) that also bore the
sickle-shaped claw. However unlike their dromaeosaurid cousins with a broader
based claw, eudromaeosaurines’ sickle claw was thinner, sharper and more
Eudromaeosaurines are further divided
into three subfamilies in being: Saurornitholestinae
(Dro-me-o-sawr-uh-nay) and Velociraptorinae
Saurornitholestine fossils have a temporal range of 77-70 mya during the Late
Cretaceous and include three medium-sized monotypic genera with all from
western N. America. The three genera of Saurornitholestinae
are: Saurornitholestes (Sawr-or-nih-tho-les-teez),
the one the subfamily is named after and is from 75 mya in the Late Cretaceous; Bambiraptor (Bam-bee-rap-tor) from 72
mya in the Late Cretaceous and Atrociraptor
(Ah-tross-rap-tor) from 68 mya.
Artist: Emily Willoughby Saurornitholestes
Saurornitholestes fossils come
from what is now Alberta, Canada and in the U.S. states of Alabama, Montana,
New Mexico, North Carolina and South Carolina. There are two species in, S. langstoni
(lang-sto-nee) and S. sullivani (sull-la-vah-nee) with both
reaching lengths of 1.8m/5.9ft. Besides the typical dromaeosaurid features like
the sickle-shaped second toed claw, both species were distinct. With fang-like
teeth in front of the mouth as other dromaeosaurids had, additionally the skull
had an unusually large olfactory bulb, suggesting it had the keenest sense of
hearing over all other dromaeosaurids along with an excellent hearing
Artist: Jonathan Kuo S. sullivani
Found on both sides of the ‘Western
Interior Seaway’ Saurornitholestes fossil
discoveries have been numerous with dozens more of indeterminate scant finds
that are suggestive of being Saurornitholestes
Artist: Peter Schouten S. langstoni
As a small biped carnivore and
scavenger, Saurornitholestes competed
with other small theropods, like Troodon
and Dromaeosaurus, but with their
agility ran from the contemporaneous tyrannosaurids. In one S. langstoni
fossil, there were teeth serration marks on the dentary (lower jaw bone) that
match the teeth of a juvenile tyrannosaurid, such as Daspletosaurus or Gorgosaurus.
On the other hand, a fossil of a juvenile pterosaur, Quetzalcoatlus had a Saurornitholestes
front tooth embedded in a wing bone. Even a juvenile Quetzalcoatlus would’ve been way too large for Saurornitholestes to hunt down and kill as prey, for predators
throughout the eons normally seek out prey half their size to lessen injury.
What is surmised is that both were feasting as scavengers on some carrion when
a tiff between the two occurred resulting in a good bite by the
saurornitholestine inflicted onto the pterosaur. In other words, Saurornitholestes was stating, “Bug-off,
I got dibs.”
Bambiraptor fully grown
would’ve been ~1.3m/4.3ft. Although there have been adult specimens, the first Bambiraptor fossil found was of a
younger juvenile, hence the name, ‘Bambi’. This juvenile find was also
discovered by a juvenile, a 16-yr-old boy combing his ranchland for fossils
near ‘Glacier National Park’ in Montana, USA. The find was significant with its
anatomical features representing bird-like dinosaurs evolving into birds. As
birds, it possessed the characteristic V-shaped ‘wishbone’ or furcula, which
allows birds to flap wings. It also possessed very long forelimbs and manus
phalanges (fingers) that approached the length required for flight, the
forearms folded as well.
Artist: Taena Doman Bambiraptor
What is unique to Bambiraptor is that it quite possibly had arm and manus (hand)
maneuverability features for the manus to reach its mouth, therefore enabling
it to hold its food while it ate. There were no feathers or feathering
impressions of the fossil finds, but since Bambiraptor’s
anatomy shows classic troodontid anatomy, such as the sickle-shaped second toed
claw, raptorial manus (hands) and a cladistic confirmed analysis of its phylogenetic
bracketing within feathered Paraves.
Artist: Michael B.H. Atrociraptor
Atrociraptor is a
saurornitholestine also discovered in N. America in Alberta, Canada’s
‘Horseshoe Canyon Formation’. At 2m/6.6ft long it was the largest of the three
saurornitholestines and was a bit hefty at 15kg/33lbs. Atrociraptor’s massive skull was short, but tall with a slender
lower jaw filled with large closely packed recurved and serrated teeth. The
outer teeth were paced closer to the fulcrum of the jaw’s articulation.
Although identical in form to one another, the teeth varied in size. All this
dentition arrangement just might point out that Atrociraptor was a specialist predator preying primarily on one
particular prey item.
Dromaeosaurinae ~ Dromaeosaurines
are another subgroup of eudromaeosaurine dromaeosaurids that had a temporal
range of ~ 130-66 mya in the Early-Late Cretaceous. Dromaeosaurines all have
distinctive sub-equal denticles (teeth), although they are very closely related
to velociraptorines in other ways and it has created much difficulty in
distinguishing the slight varying taxonomies between the two groups. Fossils
have been found in N. America, Mongolia and Denmark.
Currently there are nine dromeaosaurine
genera and eight of them are: Yurgovuchia
(Yur-go-vu-chee-ah) from the Early Cretaceous 130-125 mya; Utahraptor (U-tah-rap-tor) from the Early Cretaceous 126 mya; Deinonychus (Die-non-e-cuss) from the
Early Cretaceous 115-108 mya; Itemirus
(I-tem-e-rus) from the Late Cretaceous 91 mya; Achillobator (Ah-kill-o-bait-or) from the Late Cretaceous 89 mya; and
Dakotaraptor (Duh-ko-tah-rap-tor) from
the ending of the Late Cretaceous 66 mya.
The ninth one is Dromaeosauroides (Dro-may-o-sawr-roy-deez) which is known as a
‘tooth taxon’ since teeth are the only remains found thus far, unless ya count
the coprolite (fossilized do-do) flecked with fishbone attributed as being
dumped by Dromaeosauroides. The teeth
are definitively dromeaosaurine and are much like Dromaeosaurus with small distinctions, hence the name, Dromaeosauroides meaning, ‘Dromaeosaurus-like’.
Dromaeosauroides hails from 140 mya Denmark
and is the only European confirmed dromeaosaurine. Most of the 140 million year
ago Danish Mesozoic deposits are now under seawater. If the definitive evidence
holds up, Dromaeosauroides pushes eudromaeosaurines’
existence back millions of years.
Artist: Francesco Delrio Deinonychus
Deinonychus was once listed
as a velociraptorine, but is now considered a basal dromeaosaurine transitional
to velociraptorines. At 3.4m/11ft, it is the fourth largest dromeaosaurine
(3.5m/11.5ft), Utahraptor (5.7m/19ft)
and Achillobator (6m/19.7ft). Deinonychus’ multiple fossil remains of the
aged and young have been found in the U.S. states of Montana, Oklahoma, Utah
The manus (hands) of Deinonychus were very large with the
distal second as the longest and the first digit as the shortest. The pes
(foot) possessed the typical dromaeosaurid sickle claw on digit II (second toe)
that was large and formidable while used in predation.
Artist: Masato Hattori Deinonychus
With juvenile and adult Deinonychus teeth and bone bite marks
commonly found among ornithopod fossils, in particular Tetnotosaurus, it appears that
Deinonychus hunted in packs and fed on the prey in a shared communalism.
However, Deinonychus did not have
that strong of jaw muscles to bite through bone; only to scratch it, which
indeed knocked out a lot of teeth. With a bite force of only 15.7% that of an
extant American alligator, Deinonychus’
bite is more comparable to that of a wolf’s. Still strong, but not as strong as
some articles that compared it to an alligator’s biting force of 1450 N
(newtons), which is one of the strongest bites known. It’s comparable to the jolt
one would feel when a pickup truck reached the end of a rope once pushed off a
cliff taller than the rope is long with that one holding onto the other end of
Coming from the 98-83 million-year-old
‘Bayan Shireh Formation’ of Dornogovi Province, Mongolia; Achillobator lived roughly 89 mya in the Late Cretaceous. Carrying a
body weight of ~ 350kg/771.6lbs and growing to 6m/19.7ft, unlike a host of its
arboreal dromaeosaurid relatives, Achillobator
definitely was a ground dwelling predator. In addition to remaining on the
ground, the name Achillobator refers
to ‘Achilles Hero’ and for good reason; its Achilles tendons were well
developed to carry that weight and length around on terra firma.
Source: imgur.com Achillobator
When compared to other dromaeosaurines, Achillobator possesses all the related
features in the pes (feet), manus (hands) dentition (teeth) and feathering. But
the one distinctive trait that sets it apart from all dromaeosaurines and dromaeosaurids
is its pro-pubic pelvis. The most forward pelvic bone is the pubis. While all
other dromaeosaurine pubic bones point backwards as in birds, Achillobator’s points vertically downwards.
This simply is a plesiomorphic (primitive) genetic holdover from its very
distant saurischian cousin’s pelvic trait.
Artist: Nobu Tamura Yurgovuchia
At 2.5m/8.2ft long, although most of
that length is the tail, Yurgovuchia
fossil remains were found in the ‘Cedar Mountain’ and ‘Yellow Cat Member’
formations of Utah, USA. Yurgovuchia
is closely related to Dromaeosaurus, Achillobator and is even in closer
phylogenetic association to Utharaptor
as an advanced dromaeosaurine displaying a rapidly evolving species descended
Velociraptorinae~ Velociraptorines are the last
subfamily of eudromaeosaurine dromaeosaurids, with its members occurring at the
end of the Late Jurassic and Late Cretaceous Periods 151-66 mya. Before we go
any further with this, let me just state that at the moment, Velociraptorinae is a mess. Very
recently, it has been decided that all members of this subfamily are to be
moved out except for Velociraptor. Of
those that have been removed, I will list here as they are still monotypic dromaeosaurids
and do show relations to velociraptor in skeletal anatomy and morphology. Do
not be too concerned by this for science is not static, but changing
constantly. When newer revelations have come to light and are vigorously
analyzed and tested, if that new data is closer to the truth, then that material
will be fitted into the subject of questionable description either by
complimentary addition, or outright replacement of the older data.
It appears that these former Velociraptorinae members are now going
to be relegated as monotypic dromaeosaurids; they are: Nuthetes (New-thet-eez) from the Early Cretaceous 143 mya; Linheraptor (Lynn-huh-rap-tor) from the
Late Cretaceous ~78.5 mya; Tsaagan
(Sar-gan) from the Late Cretaceous 75 mya; Boreonykus
(Boh-ree-o-nye-cuss) from the Late Cretaceous 73 mya and Acheroraptor (Ah-cher-o-rap-tor) from the ending of the Late
Cretaceous 66 mya.
Currently, in the genus, Velociraptor (Vuh-loh-suh-rap-tor) there
are two species in, V. mongoliensis (Mon-gol-e-in-sis) and the
lesser known, V. osmolskae (Aus-mol-ski). V.
mongoliensis fossils, which are
numerous, come from the sedimentary redbeds of the ‘Djadochta Formation’ of
what is now the Mongolian province of Ömnögovi. V. osmolskae fossil
remains are from the same redbeds of what is now Inner Mongolia, China in the ‘Bayan
Mandahu Formation’. The redbeds are the result of an arid environment filled
with sand dunes.
Artist: Jonathan Kuo Lft: V. mongoliensis Rt: V. osmolskae
Both were small averaging 2.1m/6.9ft and
the fossils reveal quil knobs on the forearms that once held pennaceous
feathers. As in most all dromaeosaurids the tail was stiffened with long bony
projections (prezygapophyses) located on the upper surfaces of the vertebrae
beginning with the tenth vertebra extending forward in bracing four to ten more
vertebrae. However, the prezygophyses allowed horizontal tail movement. But unlike other dromaeosaurids, on the
anterior end, the skull curved upwards and was concave-shaped on the upper
surface, while convex on the lower.
The pes (foot) digit II (second toe) had
the typical dromaeosaurid sickle claw, but in the velociraptors, the claw was
shaped straighter used more for stabbing rather than for slashing. If you read Et Tunc Nulla Erat VII and recall
protoceratopsids, I mentioned a fossil find with Velociraptor and Protoceratops
preserved in a mortal combat pose after being buried alive in a sand dune
slide. Velociraptor was stabbing at the protoceratopsid’s neck in which was an
intelligent move, for that is where the carotid artery and jugular vein are
Artist: Raul Martin Velociraptor & Protoceratops’ fatal duel
The slight differences between the two
velociraptors was that in addition to both having a single row of holes called
neurovascular foramina that in life housed blood vessels and nerves in life, V. osmolskae
had a bone ridge near the neurovascular foramina whereas, V. mongoliensis didn’t.
Also, although both had jaws lined with 26-28 widely spaced teeth more strongly
serrated on the back edge than the front, there were slight differences in
tooth structure between the two. Both were scavengers and carnivores most
likely hunting in packs at times.
I will mention here two former
(Nuth-e-tease) was a small predator with a maximum length of 2m/6.6ft with its
fossil remains coming from the ‘Lulworth Formation’, a subunit of the limestone
‘Purbeck Group’, living 143 mya in what is now England. The significance of Nuthetes is that if its scant remains
hold up as a dromaeosaurid, along with Dromaeosauroides,
it will push the family lineage back tens of millions of years. The fossil
remains attributed to a sub adult consist of thecodont (teeth set in sockets) teeth
and a partial jaw. Nuthetes lived
along the shorelines of a ‘Purbeck Group’ lagoon.
Artist: Mark Witton Nutthetes
Acheroraptor was also
2m/6.6ft long with its fossil remains coming from the Maastrichtian ‘Hell Creek
Formation’ of Montana, USA. Acheroraptor,
living 66 mya at the ending of the Cretaceous, is the most derived
dromaeosaurid. Although its total length was smaller than T. rex’s head, with its
advanced sickle second toed claws it was a deadly predator to smaller animals.
Artist: arvalis Acheroraptor
The skull of Acheroraptor was long-snouted along jaws lined with dagger-like ridged teeth. Acheroraptor differed from other
dromaeosaurids in possessing a hypertrophied post-antrum (cavity) wall that
projects posteriorly into the antorbital fenestra, a maxillary fenestra
positioned low in the antorbital fossa and directly posterior to the
promaxillary fenestra, and distinctive dentition with marked apicobasal (apical
membrane facing the outside of the body or lumen of internal cavities) ridges.
Acheroraptor is a
significant N. American find, for it gives N. American dromaeosaurids a
phylogenetic framework. This phylogenetic analysis specifies that Acheroraptor is closer in relations to
Asian dromaeosaurids than it is to any N. American dromaeosaurid. As
paleontologist, Dr. David Evans points out, “The close evolutionary
relationship of Acheroraptor to a
small group of late-occurring Asian species that includes Velociraptor suggests migration from Asia continued to shape North
American dinosaur communities right up until the end of the Cretaceous Period.”
are the other deinonychosaurian subgroup besides the dromaeosaurids which are
in the family clade, Troodontidae
(Tru-don-tuh-day). Existing 130-66 mya during the Early and Late Cretaceous, troodontids
are the most basal of the deinonychosaurian clade. Remains have been found in
North America, China and Mongolia. Except for, Borogovia, which had a straight and flat claw on the second toe
that could not be held above ground, the rest of the troodontids possessed the
typical deinonychosaurian sickle claw on the second toe that was held off the
Borogovia pes; no sickle toed claw
Basically, the size of troodontids was
small ranging from Latenivenatrix in
being the largest at 3.5m/11.5ft, down to Mei,
which was about the size of a peregrine falcon at 60cm/23.6in. The distinctive
features of troodontids were in the long skull filled with closely spaced recurved
saw-edged teeth. The hind limbs were slender and long used for rapid
locomotion. The manus (hands) were large and flexible making it capable enough to
maneuver precise grasping.
The main feature of troodontids was that
the skull as the braincase, relative to body size is the largest of all known
dinosaur groups. With very large orbits (eye sockets) and a well-developed
brain cavity where sight and hearing nerve brain centers were located,
troodontids had keen diurnal and nocturnal sight as well as hearing. Many
conclude that troodontids with brain sizes proportionate to extant non-flying
birds were intelligent, but it is hard to really measure intelligence. They
might have been the smartest dinosaur, but for sure their cranial anatomy gives
evidence that they were very agile, speedy carnivores with a keen sense of
sight and sound.
Troodontid fossils and fossils of their
nest sites containing embryos show that, like birds, at least some troodontids brooded
shedding light on troodontid reproduction, again, as similar to birds, but
ground nesting birds. The troodontid body was covered in feathers and was
carnivorous, but along with some troodontid remains found in other dinosaur
groups’ nesting sites, like an oviraptorid nest with eggs, they may have also
been egg eaters. But, it could also suggest that they were prey themselves
brought to the nest site by the oviraptorid parents, or that troodontids were
nest parasites like the extant cowbird that lays its eggs in another birds nest
to be raised by the other birds. Overall, troodontids were fast and agile
dinosaurs with acute senses.
Troodontidae is divided into
three subfamilies and they are: Jinfingopterginae
(Sy-no-vuh-tor-uh-nay), and Troodontinae
Jinfingopterginae ~ is a separate
branch of troodontids that are more closely related to Jinfingopteryx than to Troodonformosus. They are basal troodontids
with a temporal range of 122-71 mya during the Early-Late Cretaceous.
The two genera of Jinfengopteryginae are: Jinfengopteryx
(Gin-feng-op-tuh-rics) from the Early Cretaceous 122 mya and Almas (Al-mass) from the Late Cretaceous
75-71 mya. This subfamily also contains a nomen dubium fossil that is a suspect
jinfengopterygine numbered as WDC DML 001 that as yet, has not been evaluated
Artist: Emily Willoughby Jinfengopteryx
At 60cm/23.6in, Jinfengopteryx was small with its remains discovered in the ‘Huajiying
Formation’ of Hebei, Province in China. It had extensive pennaceous feathering
on its forelimbs and tail, but lacked any feathers on the hind limbs. However,
it could not fly. When first discovered in 2005, it was thought to be one of
the most primitive of birds, but quick studies and a final review, found it to
be a troodontid.
J. elegans skeletal anatomy
Jinfengopteryx, due to its small
size most likely was an omnivore chasing after large invertebrates and small
invertebrates. Tiny reddish-yellow looking ‘pearls’ found in its remains’ digestive
cavity are identified as grains proving that all troodontids weren’t strict
Sinovenatorinae ~ includes all
troodontids most closely related to Sinovenator
and are exclusively from Early Cretaceous China.The four genera of Sinovenatorinae
(Dah-lye-uhn-sawr-us) from the Early Cretaceous 126 mya; Mei (May) from the Early Cretaceous 125 mya; Sinovenator (Sy-no-vah-nay-tur) from the Early Cretaceous 125 mya; Mei (My) from the Early Cretaceous 125
mya and Sinusonasus
(Sih-no-so-nah-sus) from the Early Cretaceous 125 mya.
Artist: Zhao Chuang Dalianosaurus
Described just in 2017, Daliansaurus comes from the ‘Yixian
Formation’ of Liaoning Province, China. Its remains were well preserved showing
new details of Chinese troodontids. In using osteohistological thin-sectioning
and high-resolution synchrotron-based imaging due to the excellent condition of
the fossil, scientists were able to analyze the histology of its forelimbs. In
the collective analysis, it showed that the fossil specimen’s growth
characteristics within the forelimb layered bone depositions that this Daliansaurus had passed the exponential
growth phase within its first year perishing three years later. But while even
four-years old, it still had not quite attained maximum somatic size.
Skeletal features of the forelimbs had
the humerus of the upper arm as rather long with the lower arm ulna distally
ending in three fingers on each manus (hands). Digit I’s (thumb) metacarpal
being is strongly curved in a vertical plane while the digit II (second finger)
is shorter than digit III. Digit I is the most robust with a claw bearing a
distinctive deep groove on the side.
The hind limbs’ strongly bowed femur’s
process (lateral crest) is lower than the posterior trochanter (bony
protuberances where muscles are attached to the upper part of thigh) process.
The tibia is 1.4 times longer than the femur. With its long and well-built
metatarsals and skeletal leg anatomy, at 1m/3.3ft in total length, Daliansaurus’ running capabilities were
far more developed than other troodontids.
Generally it was a typical troodontid
with the neural arches fused to the vertebral centra in the dorsal vertebrae.
But, in addition to the dromaeosaurid second toe sickle claw, Daliansaurus had an extra-large claw on
its fourth toe as well, exacting the same length of the claw on the second. The
projection of the premaxilla above the nostril is flattened, while another
projection below the nostril is straight. This is a feature of the premaxilla
where other troodontids had only one of the projections, but not both as Dalinsaurus had. It had 21 teeth in the
upper jaw and 34 in the lower with the back teeth being having serrations on
the rear side.
Artist: Todd Marshall Sinovenator
Sinovenator, as mentioned
again is the namesake to sinovenatorines. At 1m/3.3ft, Sinovenator had the typical troodontid skull, closely spaced large
numbers of teeth, sickle-like second toed claws and raptorial manus (hands). Some
distinct features were that the antorbital fenestra (opening in skull in front
of orbit or eye socket) was straight and vertically oriented. Also, the upper
branch of the premaxillae excludes the maxillae from the nostrils and the
maxillary tooth row is positioned some distance from the jaw rim. The ilium is
small in comparison to the rest of the pelvis, the ischium is bird-like, the
pubic bone was oriented to the rear and the shin bone was wide at the top
having a rectangular-like lower joint surface.
Sinovenator was a primitive
troodontid bearing similar features with the most basal dromaeosaurids,
suggesting the time of a transitional split between the two groups. The pubic
bone orientation to the rear is one such feature shared. This orientation also
points out that the forward pointing pubic bone in later more derived
troodontids was not inherited from older theropods, but evolved within the
Artist: Craig Chesek M. long
Mei, or with the
genus and specific name, Meilong was a small troodontid at
70cm/27.6in total in length found in the lower ‘Yixian Formation’ of Liaoning
Province, China. As a basal troodontid like the previously mentioned Sinovenator, but unlike the advanced
troodontids, it had bird-like hips. Mei had unique small and low maxillae with
tiny fenestrae, an extremely large naris extending caudally over one-half of
the maxillary tooth row and closely packed middle maxillary teeth with the
maxillary tooth row extending caudally to the level of the preorbital bar.
Artist: Esther van Hulsen Mei slept just like birds do today
Artist: Mick Ellison Mei
paleontologists have found their Sleeping Beauty; Mei in Chinese even means ‘sleep soundly’. With the two Mei fossil remains, both were detailed
in a 3-D sleeping pose. The pose is much like birds roosting with the head
tucked in between a wing and the body, while the body rested over the bent
legs. The surrounding matrix of the fossil sites is volcanic ash and it appears
the two asphyxiated from volcanic gaseous then quickly buried by the ash; much
like what occurred during the Pompeii eruption.
With the 3-D fossilization imaging of
the two Mei remains, the evidence
points to the fact they died in a life sleeping pose rather than coincidental
rigor mortis. This form of sleeping suggests that Mei was warm-blooded.
Troodontinae ~ are a group
of closely related troodontids descended from their common ancestors of Gobivenator and Zanabazar. The ten genera from Troodontinae
(Sy-no-nif-oi-deez) from the Early Cretaceous 113mya; Urbacodon (Ur-bah-koh-don) from the Late Cretaceous ~ 95 mya; Troodon (Tru-o-don) from the Late
Creataceous 77.5-76.5 mya; Stenonychosaurus
(Sten-o-nick-o-sawr-us) from the Late Cretaceous 76 mya; Latenivenatrix (La-ten-eye-vuh-nay-trics) from the Late Cretaceous
75.5 mya; Saurornithoides
(Sor-orn-nih-thoy-deez) from the Late Cretaceous 75 mya; Linhevenator (Lin-he-ven-ah-tor) from the Late Cretaceous 75 mya; Philovenator (Fie-lo-ven-ah-tor) from
the Late Cretaceous 75 mya; Gobivenator
(Go-be-ven-ah-tor) from the Late Cretaceous 72 mya and Zanabazar (Zah-nah-bah-zar) from the Late Cretaceous 70 mya.
Stenonychosaurus comes from the
Late Cretaceous ‘Dinosaur Park Formation’ of Alberta, Canada and nesting sites
in ‘Two Medicine Formation of Montana’. It was 2.4m/7.9ft in length and stood
up to 0.9m/3ft in height. As mentioned earlier, where troodontids had the
largest brain size of any other dinosaur group when compared to body size, Stenonychosaurus had the larger brain
when compared to all other troodontids. When compared to other species with the
same body weight, Stenonychosaurus
shows a steady increase in the encephalization quotient (EQ) of brain weight. Its
eyes, as testified by the fossils’ orbits (eye sockets) were also the largest
troodontid eyes that probably afforded excellent diurnal sight, but superb
nocturnal sight. The position of the orbits slightly faced forward, which also
enhanced vision with depth perception.
Credit: Thomas Henry Huxley Paleozoology Gardens Stenonychosaurus
The jaws of Stenonychosaurus met in a broad U-shaped in an adhesion of fused
fibrocartilaginous tissue known as ‘symphysis’.The denticles (teeth) bore large serrations with pits between each denticle
(tooth). According to the type of teeth, Stenonychosaurus
may have been an omnivore. The grasping manus (hands) ended in three flexible
fingers. Analyzing Stenonychosaurus’
fossils’ ring bones, it reached full maturity by 3-5 years.
Stenonychosaurus fossilized eggs
Studying nesting fossil sites and their
embryos in Montana’s ‘Two Medicine Formation’, it has been determined that they
are Stenonychosaurus embryos. The
nests were dish-shaped fashioned, rimmed with hardened mud and filled with
sediment. Up to sixteen elongate and teardrop-shaped eggs were laid being
positioned vertically with the tapered end buried in the pebble sediment.
at 1.8m/5.9ft appears to be an Asian counterpart to the North American, Troodon as they both share many
morphological and physiological features. Both shared similar size large orbits
(eye sockets) and due to the large braincase that housed a large brain compared
to body size, both shared similar intelligence.
Artist: Linda Krattiger Saurornithoides
Saurornithoides was discovered
in the ‘Djadochta Formation’ of what is now Mongolia and had the typical
troodontid large number of closely spaced serrated teeth on the rear side.
However, its evolvement is transitional as Saurornithoides
still retained a basal presence in possessing a recessus tympanicus dorsalis (the
upper one of three small openings on the side of the braincase within the inner
ear region), but exemplifies a more derived form in lacking a small opening at
the front of the snout called a fenestra promaxillaris. In possessing more
derived traits, it also had large denticles on the rear tooth edges as well as
the high number of six sacral vertebrae.
With a body length of 3.5m/11.5ft, Latenivenatrix was the largest of
troodontids so far discovered. Also coming from the upper ‘Dinosaur Park
Formation’, it was discovered in conjunction with the Stenonychosaurus remains. The distinction between the two is due to
the varying frontals, Digit II (metatarsal two) structures and of course size.
Both of these troodontines were originally assigned as Troodon. As well, both species phylogenetically are closer to the
Mongolian troodontid taxa indicating an earlier Asian troodontid form migrating
into North America.
Artist: Julius T. Csotonyi Latenivenatrix
Latenivenatrix differed from
other troodontines in having a slightly retroverted (tipped backwards) pubis
with a shaft that curved anteroventrally, whileslightly proximal to the pubic
boot is a large muscle scar on the lateral surface of the pubic shaft. It
maintained troodontine traits in possessing an elongated ambiens process and
has a horizontal ventral margin of the postacetabular process and of course had
the dromaeosaurid and troodontid pes digit II (second toe) sickle-shaped claw.
As far as paleopathology goes, in one of its fossils, a catalogued parietal
bone possessed an aperture that was caused by a cyst resulting in a bite wound.
Gobivenator’s remains were
found in, you guessed it, what is now the Gobi Desert of Mongolia from the ‘Djadokhta
Formation’ that is part of the 75-71 million-year-old ‘Campanian’ stratigraphic
range. The Gobivenator fossil remains
are the most complete and articulated yet of any troodontid.
The typical characteristics of troodontids
were also displayed in Gobivenator’s
remains such as the digit II (second toe) sickle claw, raptorial manus (hands),
closely spaced teeth in the lower jaw and a graceful frame geared for swift
running. What makes it unique is in its autapomorphic (derived trait) features
having the parietal bones fused ending anteriorly in a pointed tip, the lower
jaws’ surangular (jaw bone found in all land vertebrates, except mammals that
connects all jaw bones) has a fossa (a bone depression) and the skull had a
large fenestra (opening).
Artist: Eloy Manzanero Gobivenator
Gobivenator possessed an
akinetic skull, however it had lost the epipterygoid (a slender skull bone
found in reptiles) bone and there was a reduction in contact between palate
bones. These were the preconditioned initial features evolving towards cranial
kinesis found in birds.
There are nine troodontid genera which
are monotypic outside the subfamilies; they are: Albertavenator (Al-burr-tuh-vah-nay-tur) from 130 mya; Geminiraptor (Gem-in-i-rap-tur) from 127
(Lee-ow-ning-o-sawr-us) from 126 mya; Jianianhualong
(Chon-e-an-wuh-lon) from 124.4 mya; Xixiasaurus
(Zee-zee-ah-sawr-us) from the Late Cretaceous 86 mya; Byronosaurus (By-ruh-no-sawr-us) from the Late Cretaceous 80-75
mya; Talos (Tay-luhs) from the Late Cretaceous
75.95 mya; Borogovia
(Bow-roe-go-vee-ah) from the Late Cretaceous 70-65 mya and Tochisaurus (To-chee-sawr-us) from 69 mya of the Late Cretaceous.
Artist: Weldon Owen Byronosaurus
Discovered in Mongolia’s Gobi Desert on
separate occasions, Byronosaurus
adult remains were found in two sites, while in a third location nearby at a
nesting site, two near hatchling embryo skulls were found still with egg pieces
clung to them. This poses a bit of a conundrum, for the nesting site was not a Byronosaurus nest, but an oviraptorid
nest with eggs in it while one egg having a preserved oviraptorid embryo. How
did they get there? Were the Byronosaurus
hatchlings preying on the eggs for their first meal, or did the oviraptorid
parents seize the Byronosaurus hatchlings
or near full term embryos for their meals, or, was Byronosaurus a nest parasite?
Byronosaurus embryonic skulls
At 1.5m/4.9ft long, Byronosaurus shares troodontid traits, but the teeth were not
serrated. The teeth were needle-like most suited for grasping and seizing hold
of small vertebrates. Living in a desert, the fossils were found near streams,
so with its teeth built for capturing and holding on to struggling or slippery
prey, it may have been a piscivore as well. The metatarsals (foot bones) were
proportionally long compared to the body and along with the gracile long hind
limbs, it was built for speed.
Artist: Julius T. Csotonyi Jianianhualong
Jianianhualong fossil remains
were found in what was Early Cretaceous China. At 1m/3.3ft long, the fossil is
exceptional in giving vivid detail on skeletal anatomy and feather impressions.
Jianianhualong possessed both
features of basal and derived troodontids. Unique among troodontids, it also
had the neural spine of the axis convex shaped on the top margin with the
portion strongly expanded. The dentary bones supported 25 teeth on each side
while the maxillaries supported 21 on each side. The teeth were closely packed
up front and not serrated differing from the back teeth that were more spaced
and had serrations on the back side.
The tail and forelimb feathering are
pennaceous and asymmetrical, the feathers that birds actually take flight with.
Although Jianianhualong could not
fly, with its long hind limbs, it was a probable and agile sprinter and the
tail wings would have afforded drag in maneuvering. But, with asymmetrical
feathering already in place as so explicitly detailed in Jianianhualong’s 124.4 mya fossil remains, through a bit more
flight evolvement, birds were able to take wing and fly.
Talos is a troodontid
representative from the N. American ‘Kaiparowits Formation’ in what is now
Utah. At 2m/6.6ft, it was one of the larger troodontids and coming from the
same region and time, in what was then the southern portion of the Laramida
Island, as T.rex and other tyrannosaurs like the genus, Teratophoneus or Lythronax
may have been one of the larger dinosaur’s conceivable snacks.
Artist: Jorge Gonzalez Talos & its sharp claws
It had the troodontid characteristics of
a feathered body, raptorial manus (hands), a retractable second toed sickle
claw, bore weight on the other two toes of each leg and had a large brain. In
addition it had its own distinct features in unlike most troodontids, the Talos neural arch of the mid dorsal was
pneumatic. Where most troodontid mid dorsal neural arch spines were short and
fan-shaped, the Talus mid dorsal
neural arch spines were long. As shared with Mei, projection of the dorsal periphery of the parapophyses (ventral
transverse process of a vertebra) may reflect incipient development of the
stalk-like condition in dromaeosaurids. The most distinct feature was that the
neural spine tapers to a dorsocaudal (top of tail) point in lateral profile.
Artist: Julio Lacerda Troodon in Alaskan winter
paleoenvironment showed that by living in forested wetlands and floodplains,
which was in contrast to the desert paleoenvironment of its Mongolian cousins,
troodontids were adaptive. Even in Cretaceous Alaska where the average winter
temperature was 2° C/36 F° and snowed during winter months of long cold
darkness, troodontids were able to successfully inhabit these climatic
conditions. In fact, from the number of fossil finds and amount of loose teeth,
Troodon was the most common dinosaur
found in Alaska’s ‘Prince Creek Formation’ making upwards to two-thirds of all
species. This feathered Troodon and
the other two troodontids gives us insights into how animals physically and
physiologically adapted to environmental contrasts.
Artist: Oliver Demuth Albertavenator
Found in the ‘Horsehoe Canyon Formation’
of Alberta, Canada, Albertavenator is
another N. America troodontid reaching ~ 1.8m/6ft in length. The supraciliary
foramen (bone ridge located above eye-sockets) is truncated anteriorly by the
lacrimal (small bone forming the eye-socket) contact. Dentition is very similar
to the synonym, Troodonformosus from the ‘Dinosaur Park
Formation’, but the skull overall is much more robust and the ectocranial
(outside cranial surface) of the frontal bone is much shorter than all other
In the next Et Tunc Nulla Erat series we’ll dive into dinosaurs that begin to
not only appear as birds, but evolve as birds.
Apologies for the delay in getting this
article published. I had already written it by May, but to edit it and upload
the photos had to take a back seat to other concerns. Anyway, here it is…
Here’s to hoping that ya all had a Happy
Turkey Day and, from the Grand ol’ White Bearded One (Santa Claus), are hand
delivered a most joyous occasion this Christmas season!
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