Et Tunc Nulla Erat VIII Dinos 1

Et tunc nulla erat VIII
(And Once There Was)
Dinos: Part 1of 2

The Path to Dinosaurs:
To set the stage of the environment dinosaurs evolved from, lived and reigned in, we’ll first start off with period events that took place during dinosaurs and birds. Below is a description of the fauna, flora, geological, climatic and catastrophic events during which time dinosaurs would later evolve as a result of.

The Early Triassic
The Triassic is sandwiched in between two mass extinctions. The first is called ‘The Great Dying’ occurring between the Permian/Triassic border ~ 252 mya during Pangaea (Pangea). The second occurred at the Triassic/Jurassic during the initial breakup of Pangaea ~ 201.3 mya.

It’s called ‘The Great Dying’ for a valid wiped out 96% of all marine species, 70% of all terrestrial vertebrates and nine out of every ten plants, destroying Permian conifer forests en masse. It even exterminated insect groups in killing off 57% of all insect families and 83% of all insect genera, which included Earth’s largest insects like the 70cm/27.6in wingspan dragonfly, Meganeura and other arthropods including the largest land invertebrate ever in the millipede, Arthropleura. This is thus far the only mass extinction of insects.

The only surviving vascular land plants to support any animal life were lycophytes, one surviving ginkgophyta species, ferns, the seed fern Glossopteris, some conifers in highlands and bennettitales. However, this opened a window for spermatophytes (seed plants) to take hold and later dominate in the Cretaceous.  

‘The Great Dying’ event was so catastrophic that from oceanic molluscs to dominant land vertebrates, 96% of eukaryotic life became extinct. Within 100,000 years, the blink of an eye in geological time, life was nearly eradicated. There was no one culprit which is why it has been hard to pin down. But recent paleo stratigraphy analyses have unearthed the mystery surrounding this mass extinction.

Falkland Islands Impact Site
Around 252 mya, an asteroid smashed into Earth, with remnants of the massive impact crater located near the Falkland Islands. The crater, now buried in sediment, was first discovered through very erratic NASA gravity anomalies. Later, magnetic imaging and seismic data helped verify the 255km/155mi wide crater.

Falkland Islands Gravity Survey
This impact was much larger than the 180 km/112 mi wide Chicxulub impact crater off the coast of the Yucatan Peninsula that finished off the dinosaurs 186 million years later. ‘The Great Dying’ hyper velocity impact sent billions of US tons/kilograms (1 US ton = 907.2 kg, 1 billion US tons = 907,184,740,000 kg) of particle debris into the atmosphere. Along with the particulates, clouds of noxious gases rose blocking out sunlight for months on end.

The initial impact on life was exacerbated even more due to another impact around the same period (254.7 ± 2.5). A smaller asteroid, known as the Araguainha Crater slammed into oil shale strata of present day Brazil. In conjunction, these two asteroid impacts shook the globe in tremors unlocking and spewing out escaping underground oil and gas creating massive fires and explosions. Immense coal beds from the Carboniferous were also ignited.

On top of all this, the active ‘Siberian Traps’ volcanism was jolted into high gear from the asteroid impact. These traps spewed out basaltic lava covering roughly 2 million square km/770,000 square miles before its mantle plume played out in the Triassic. Superseding the volcanic ‘Emeishan Traps’ of present day China that played out at the ending of the Permian 259 mya, the massive volcanism also emitted ash dust, pyroclastic debris and the gases: hydrogen chloride, hydrogen fluoride, hydrogen sulfide and sulfur dioxide. Once in the atmosphere, these gases aerosolized in reacting with other atmospheric components.

This was in effect two pulses of extinction activity, for of course all the volcanic emissions aided the asteroids’ impact dust particulates in blocking out sunlight and heat causing a cooling down effect. The aerosolized gases displaced normal atmospheric conditions turning it into noxious and corrosive acids that reigned down on Earth as rain and snow.

With sunlight and warmth blocked by the asteroid impacts and volcanism, the resultant cold darkness and acidification wiped out photosynthetic plants such as purple algae, green algae and phytoplankton. These were the base and foundational building blocks of the food chain. Thus herbivores would starve, which in turn starved out carnivores.

All of this even created a third pulse. The gases reacting to atmospheric elements such as water molecules, nitrogen and oxygen produced hydrochloric acid, nitric acid and sulfuric acid that in turn acidified rain and snow. But the main gas culprit to come was carbon dioxide.              

The Permian, although under the ending of the significant Permo-Carboniferous glaciation, was trending towards a hot climate during the Late Permian. This was compounded and accelerated in the Early Triassic with the release of carbon dioxide from the asteroid impacts and volcanism in the volcanic activity’s initial release of subterranean heat trapped gases and the releasing of heat trapping gases from the lava flows igniting gaseous and liquid hydrocarbons that were once trapped in underground rock strata, or in solid form such as coal veins.

Once all the initial debris and gases were washed out of the atmosphere, the vast amount of carbon dioxide and carbon monoxide remained heating up the atmosphere even more. With the abundance of heat trapping gases in not allowing reflected infrared heat to escape, much of the excess gases were absorbed by ocean waters. This acidified the waters by dissolving the inorganic carbon dioxide and carbonates in situ into carbonic acid deep in the waters due to the fact warmer water sinks. This in turn freed up sea floor methane hydrate, frozen from the cold and pressure, releasing megatons/mega-kilograms of methane gas that is 27 times more efficient in trapping heat than carbon dioxide is. As the Late Permian was already heating up, this accelerated the process.

Due to this, by the time the Triassic Period was initially underway, atmospheric and oceanic runaway heat was devastating life. Marine species such as blastoids, eurypterids and trilobites, among others all went extinct.

The more Earth’s climate heated a deadly march down from glaciation to hothouse incurred. In less than two million years into the Triassic, there was no evidence of polar glaciers. Even the permafrost melted with its immense amount of frozen organic debris. Once unfrozen it began to decompose releasing locked up carbon dioxide. The decomposers were bacteria and in the process, the bacterium produced methane as waste, further acerbating the broiling heat up. 

How do we know of this...the history of the episode is literally written in stone and we’ve finally learned how to read it. We now know this for a few reasons that correlate the time period’s demise for life. One was in finding and dating the asteroid craters and analyzing their intensity. In judging the expansive perimeter and mantle depth of the Falkland Islands impact, its energy force was equivalent to 120.4 billion Hiroshima A-bombs. This immediately wiped out surrounding life.

Two, after the Falkland Islands impact intensified the Siberian Traps, the immediate surroundings supporting plants were wiped out. In addition, the gases and particulate debris added to the impacts’ blocking out of sunlight, killing off much of Earth’s photosynthetic plants, thus starving off herbivores, then lastly the carnivores. This is detected in the increase of fungi spores and microorganisms embedded in the fossil record that fed off dead organic material. Also, the nickel eating archaeon, Methanosarcina experienced population explosions resulting in blooming extensively throughout the oceans.

This archaeon microbe, which still lives inhabiting the deep oceans and mammal guts, combines carbon dioxide with hydrogen gas, metabolizing methanol or methylamines producing most of the biologically-generated methane released today. The nickel content came from the volcanism that the archaea consumed and metabolized. The by-product of this metabolism was the release of immense amounts of methane that displaced oxygen in the oceans while the amount of methane that escaped into the atmosphere further added to the earth’s trapped heat.

Three, as stated earlier, after all the debris and gases were washed out of or dissipated from the atmosphere, a vast amount of greenhouse gases remained heating up Earth’s atmosphere and oceans, causing a shift in the oceans’ currents. This, in conjunction with the greenhouse effect, was the long term culprit that killed off life that had managed to survive through the initial two stages.                                            

Oceans absorb heat energy from the sun and carbon dioxide from the atmosphere. Oceanic stratified currents move the energy from areas of hot water to areas of cold water, and vice versa. Not only does oceanic current circulation keep the water temperature moderate, but it also affects the temperature of the air and disperses nutrient rich waters in ocean regions that are depleted.

Oceanic Current Stratification 

The oceanic current stratification remains separate due to halocline (salinity), thermocline (temperature), oxygenation (chemocline) and pycnocline (density) variables. Baroclinity (baroclinic stratified fluid as measured between the differences of gradient pressure from the gradient of density) is what maintains a parallel stratification. Wherever they pop up, upwelling or downwelling eddies create turbulence mixing the stratified waters. Mixing layers interchange nutrients and acts as a station pump for current circulation.

When Earth’s water bodies had heated up due to the runaway greenhouse effects, it began homogenizing the waters’ temperatures, Warmed water rises as cooler waters sink. This is the initial force in circulating ocean currents. With waters approaching the same temperature range from the increasing heat, circulation stopped. In so doing, except along a few coastal shorelines, most of the Panthalassan Ocean and Tethys Sea bodies became devoid of nutrients and thus void of higher lifeforms. This created a global dead zone.

First off, when circulation ceased, the deeper waters became stagnant by losing dissolved oxygen (DO) as warmer waters released dissolved oxygen content replacing it with carbon dioxide. This created hypercapnia conditions putting excessive carbon dioxide into the bloodstream of aquatic animals that lead to breathing problems. This further led to hypoxic environments, where with little oxygen left animals could not maintain breathing thresholds so those that could move out did so to shallower environs. As carbon dioxide further increased, the warming ocean depths further heated up creating an anoxic environment virtually empty of dissolved oxygen. For those aquatic animals that were more sessile than mobile they couldn’t swim away. Unfortunately for marine forms like molluscs, echinoderms and sponges, they simply perished. In addition, anaerobic bacteria began proliferating in the depleted DO waters producing toxins that were lethal to aerobic organisms.
Early Triassic Dead Zone

However, even where marine animals were moving into shallower waters just to breathe, most coastal shores were heating up as well and with the acidification of the waters, corals began dissolving creating a supported communities die off. Reef making animals during the Permian that went extinct amid ‘The Great Dying’ were: calcisponge (sponges with calcareous spicules), algae/bryozoan reef builders and rugose colonial corals. Along the coastal Tethys seas’ shorelines were about the only escape for marine animals from the anoxic and heated/acidifying waters.      

Almost in a page by page fashion in flipping through a history book, we know this occurred by observing fingerprints in the stratified layers of rock and fossils. In an older layer of bedrock there are many examples of fossils that represent animal deaths, while the latter formed upper layers of rock show no evidence of fossils.

Except for the terrain higher elevations, anywhere else on land all the conifer forests perished with a big influx in fungal spore fossils that decomposed the dead trees. The mean oceanic temperature along the equator’s perimeter reached a maintained 40°C/104°F. Terrestrial temperatures ranged from 49°-60°C/120°-140°F.  Anoxic conditions from the entire ocean depths to the interior of Pangaea laid waste in creating a desolate watery grave and desolate hot desert. Only 4% of all ocean life and 30% of vertebrate terrestrial life survived.

δ13C did not recover into positive integers until 244 mya. Life did not rebound until the Middle Triassic and took thirty million years into the Late Triassic to build up biodiverse ecosystems and complex food webs.      

Isotopic signatures are a valid way in interpreting, fossils, paleoclimatology, paleoceanography, and geochemistry. δ13C (Delta 13C isotope) and δ18O (Delta 18O isotope) are stable isotopes that occur in nature. The atomic mass of isotopic variance affects an isotope’s chemical kinetic behavior which leads to natural isotope separation processes. This is stored in the bedrocks of former paleo-geographic conditions. Through isotope ratio mass spectrometry, it tells us what isotopes were laid down in the rock strata at the time, which in turn tells us what those conditions were.
Above and to the left here, I showed the formulations of the isotopes, 13C and 18O as ratioed between unstable isotopes of 12C and 16O respectively. Events like rising temperatures or biogenic methane isotopes affect the ratios. I’m not going to get too involved in this as its details could be treated in a long-winded treatise of its own and I’m sure most of us want to get to dinosaurs. However, I will attempt to explain a bit of it.

The referenced formulas are the standards for established material that depict an increase or decrease in the abundance of the two isotopes and are displayed in parts per thousand (PPT or per mil); that is what the 1000 ‰ stands for. It will have a negative value when an unstable isotope supersedes 13C or 18O and will have a positive value if these two elemental isotopes possess a higher number once ratioed.  

For instance, carbon isotopes are utilized by plants differentially during photosynthesis, yielding a positive δ13C value. With this information, we know there was enough plant life to sustain animal life. But if they yield a negative value, such as large amounts of methane affecting the mass ratio of 13C to an impinged higher value to 12C, then we know there was an impact occurring on life. δ13C varies in time as a function of productivity, C2 abundance, organic carbon burial, methane amounts and vegetation type.

The same results occur with δ18O. This oxygen isotope’s negative or positive time shell variances detects atmospheric and ocean temperatures, evaporation/rain rates, O2 atmospheric/oceanic volumes and ice sheet transgressions or recessions.

Also, cosmogenic isotopes formed from the interactions of high-energy cosmic rays and meteorite impacts affect Delta isotope ratios. 

Correlating this information all together with other isotopic analyses and with the fossil record, a design of events comes into play. Mass extinctions are signatured by negative δ13C and δ18O anomalies representing a decrease in primary plant productivity (O2 intake in life) and release of plant-based carbon (sequestered C2 liberation upon death). These laid down isotope signatures embedded in rocks work just as well for today’s analyses as they do for earlier periods in Earth’s history and that is telling of what is occurring right now with climate change.  

Study the illustration below. It’s an interesting comparison of Earth’s atmospheric conditions from the outbreak of ‘The Great Dying’ to now. In particular compare the earth to 250 mya to the 2090’s. They are very similar and please recall that ‘The Great Dying’ killed off 90% of all species. Earth’s abbreviations in the stages are:
P/T ~ The Permian Triassic boundary
LPTM ~ Last Paleocene Thermal Maximum
LGM ~ Last Glacial Maximum
LIA ~ Little Ice Age
A2 ~ Additional Emissions (Anthropogenic/Manmade) 

The above graph, measured in Milankovitch cycles, is data pulled from Vostok Antarctica ice cores going back from the present to 420,000 years ago. Milankovitch cycles take into account and factors in Earth’s cyclical orbit of eccentricity, axial tilt, and precession. The blue lines on the chart measures CO2 levels, the red ~ temperature range, the green ~ measures methane levels while the bottom orange line measures δ18O anomalies.     
The graph below is a 5.3 million year change in climate in comparing δ18O oceanic benthic carbonate anomalies to the Vostok ice cores. Please note between 5.3-3.1 mya there was a warm period due to high levels of carbon dioxide with a mean global surface temperature increase of 2-3°C/3.6-5.4°F.

In going back to the last graph, overall the last three million years experienced cyclic glacial and interglacial periods. Before that, was a period when atmospheric CO2 levels ranged from 350-400 ppm heating global climate. Today, as of March 2017, Earth’s atmosphere is at 406.99 ppm saturation levels, in which by total mass, is over 850 gigatons. Currently we’re averaging 3 ppm per year increases. At that rate and with its current exponential gains, CO2 atmospheric saturation will exceed 500 ppm by 2047. Once this happens global temperatures will rise 3°C/5.4°F.

What will our world look like at this increase? Well mankind will still survive, but at an egregious cost. Crop and food production will be cut short. Due to regions becoming very arid, there will be massive immigration influxes. There will be a massive uptick in people dying from heat stroke and regional fresh water supplies will be drained from extended droughts.  

Currently there are some 123.3 million Americans living along U.S. coastal shorelines. There will be no stopping of the Greenland and West Antarctica ice sheets from totally melting adding all that once frozen water into the oceans raising coastal shorelines 10.1m/33ft. With a mass volume of 0.11 trillion cubic m/2.1trillion cubic ft. of water, compare that to Mt. Everest weighing 161.9 trillion kg/357 trillion lb. In converting volume to weight, a NASA and University of California at Irvine analysis already shows western Antarctica’s current lost frozen water has been equivalent to the weight of Mt. Everest every two years for the past 21 years. One thing is for sure the coastal waters are coming.

During the PETM (Paleocene Eocene Thermal Maximum) ~ 55.5 mya, a large decrease in 13C/12C ratios of marine/terrestrial carbonates and organic carbon occurred inducing global warming. CO2 atmospheric and oceanic increases were due to an averaged atmospheric temperature rise of 6.75°C/12.15°F; although the exact cause still perplexes geologists. The PETM is a focal indicator for scientists, because it represents the best analogy of current global warming events with massive carbon inputs into the atmosphere and oceans, along with the accompanying acidification of marine environments. The PETM was a runaway mini hot event that ended as quickly as it came lasting ~ 200,000 years. But in comparing, it averaged only 0.37 Gt/yr, where currently under human emissions, 10 Gt/yr are being released.

Below is a NASA video of CO2 in Earth’s current atmosphere. It’s a tad alarming. In particular when there are those in political leadership that have no proof to their denying claims whatsoever, so resort to bashing climatologists, who’ve done the work and once they announce proof from decades of empirical studies, deniers only throw doubt into the winds. Economic greed and wielding power is the only slanted view climate change deniers can offer.

Some deniers partially acknowledge current global warming, but like to claim it is a natural event that has happened many times before. But they stop there and don’t proceed on explaining the resultant mass extinctions that ensued. A baked Earth is a dead Earth for life as we know it. We only have one home...Mother Earth...if we don’t keep the front porch swept clean there is nowhere else to move to.

After ‘The Great Dying’, by the time life had rebounded in the forms of archosaurs and synapsids, another mass extinction event unfolded 201 mya at the boundary of the Triassic and Jurassic. Primitive dinosaurs had already evolved during the Middle Triassic, but nonetheless, in this mass extinction an estimated 76-84% of marine and terrestrial species went extinct. However, the dinosaur line survived to become the dominant order during the Jurassic and Cretaceous. Massive emissions of carbon dioxide, sulfur dioxides and aerosols from intense volcanic eruptions initially created a cooling effect, afterwards an extreme warming period ensued. This is the consensus in the main energetic force that created the extinction. The breaking up of Pangaea’s tectonic plate movements created the volcanism that in turn made up a global environment of both, a critical CO2 greenhouse and a marine biocalcification crisis.
The Cretaceous/Paleogene (formerly Tertiary) mass extinction unfolded 66 mya wiping out all non-avian dinosaurs. An estimated average of 76% of all marine and terrestrial species became extinct. The main significance of the mass extinction was due to the Chicxulub impactor that will be discussed in fuller detail later on.

The Chicxulub Crater Asteroid Impact
These three mass extinction events are what formed, molded and lastly became the demise of nearly all dinosaurs. The Triassic, Jurassic and Cretaceous periods are what also molded our modern day insects. ‘The Great Dying’ also afforded insects a rapid adaptation to selective environmental pressures. While modern orders began showing up in the Triassic including Homoptera (grasshopper, locusts and cricket groups), most modern insect families first appeared in the Jurassic while the symbiotic relationships of insects to the appearance of flowering plants occurred in the Cretaceous. Within a span of 100 million years during these periods, insects had diversified inherently into modern day forms.

As dire as the ‘The Great Dying’ was to Earth’s life, its aftermath on climate change is what promoted the dinosaur lineage evolvement. With only pockets of regional woods left, from once vast interconnected forests and tropical jungles, it isolated species members allowing natural selection to take effect on the surviving archosaurs to evolve biological phylogenetics to better manage the stresses of newer environmental conditions. The further global isolation caused by continental drift then exploded dinosaurian speciation allowing them to enjoy a 180 million year run. Now that is species genetic transfer success...

The Road to Dinosaurs:
The primary tetrapodal survivors of ‘The Great Dying’ were the synapsids, in particular in the order, Therapsida (Phonetics: Thur-app-see-duh). In fact, accounting for as many as 95% of the total individuals in fossil beds, Lystrosaurus (Liss-tro-sore-us), an herbivore therapsid was the most common terrestrial vertebrate in the Early Triassic. With a horny beak and the ability to dig for roots and burrow, gave Lystrosaurus an advantage in eating varied rough, gnarly vegetation and refuge from the extreme climate. Also later in the Triassic, bees evolved from wasps in conjunction with the spread of angiosperms (flowering plants) as insect amber fossils give evidence to transitional hymenopterans.

Artist: Julio Lacerda the Therapsid, Lystrosaurus
Some archosaurian lines managed to survive as well that eventually led to crocodilians. Poposaurus (Pop-o-sore-us), Prestosuchus (Press-toe-sue-cuss) and rauisuchids were, among others, sister groups to crocodylomorphs under the clade, Loricata (Lore-ee-caw-tuh). Some of the early dinosaurs were on their menu, but it was the lystrosaurs that sustained dinosaurs during the Early Triassic. They all, except for the crocodylomorphs went extinct at the end of the Triassic.

Artist DanOs  the archosaur, Prestosuchus
Another archosaurian line, the avemetatarsalians also managed to escape extinction during ‘The Great Dying’. The basal avemetatarsalian, Sceleromochlus (Sclair-o-mo-klus) was a small insectivore that its ancestral line also survived the mass extinction. Showing up in the Middle Triassic it lived a desert life with anatomical features to accommodate a sandy and hot lifestyle that would be an advantaged inherited pickup for theropod dinosaurs.

Artist: Mark Witton  Scleromochlus
Sceleromochlus, with a narrowing of the metatarsal, elongated distal hind limbs and a reduction of the lateral pedal digits, this creature was a bipedal cursorial animal geared for speed. For energy conservation in a sandy environ, it was most likely saltatorial (hopping) as well in locomotion. At the end of the femur was a pronounced intercondylar groove that supported a large quadriceps femoris tendon for hopping. At only 18.1cm/7.1in, this avemetatarsalian had a long tibia and fibula between the knee and ankle and with posteriorly flattened metatarsals was able to squat or crouch down on the ground in plantigrade fashion without the feet sinking into sand.

To escape daily heat, it was likely nocturnal, as betrayed by the very large skull orbits, seeking protective shelter from the heat during the day. Sceleromochlus most likely, due to its desert environmental evolvement, possessed filaments or fuzz, an anatomy trait that pterosaurs and theropod dinosaurs would inherit in pycnofibers and feathers. Right at the edge of transitioning, Sceleromochlus is a direct ancestor to ornithodirans.

Below is a Triassic Period graphic of the animal evolvement lines we’re about to discuss showing when and where they first evolved.

After archosaurs split into Pseudosuchia (the crocodile line) and Avemetatarsalia (bird-like line) around 249 mya, by 245 mya, avemetatarsalians further divided into two more groups in the clades, Ornithodira (Or-nith-o-deer-ah) and Aphanosauria (Ah-fan-o-sar-ee-ah) evolved. Aphanosaurs are the older of the two clades showing up 245 mya in the genera, Yarasuchus (Yar-ah-sue-shis) and Dongusuchus (Don-goo-such-is). The recent discovery and 2017 description of, Teleocrater (Tell-ee-awk-rah-tur) also was found in sediment laid down ~ 245 mya. Between 1.8-m/6-10ft long resembling a modern day monitor lizard, it possessed avemetatarsalian skull features in jaw muscle attachments, but also had pseudosuchian traits in ankle joints enabling side to side rotation.
Artist: Mark Witton  Teleocrater
Aphanosaurs are fourth to fifth removed cousins to dinosaurs that did not have distinguishable stem avian features as ornithodirans, but had a physiological mix of dinosauriform and rauisuchian physiognomies. Aphanosaurs were carnivorous quadrupeds, except that Yarasuchus had capabilities to rear up on its longer hind limbs utilizing locomotion as a biped. Spondylosoma (Spawn-dill-o-so-ma) may be a basal ancestor to the primitive herrerasaurid dinosaur family, but is more of an outside sister group to the other three aphanosaurs making it a polytomy phylogeny. This is due, in that Spondylosoma does not share in the fifteen anatomical characteristics that the other three do. The same polytomic relationship goes for lagerpetids toward dinosauriforms. This signifies that both these species were more basal in ancestry being more related to the common ancestor it came from than with the more derived forms that share more traits among their groups.
Simple Ornithodira Cladogram

Ornithodirans, which includes dinosauromorphs and pterosauromorphs, had on the fourth trochanter of the femur an enlarged ridge located low down the ankle joint. This modified and advanced the metatarsal ankles into a simplified hinge-like arrangement with the astragalus and calcaneum reduced but firmly attached to tibia and fibula hind leg bones.

Ankle comparisons

Ornithodiran ankles

Autopodium (plural: autopodia) in paleontology is the distal endpoint (foot, hands) and measurement of a limb. As most fossils do not have all four limbs intact, fossil foot imprints left by the animal is a good way in evaluating, stance, stride, morphology, anatomy, correlation and identification of species. There are basically two autopodia observed in fossil studies and that is the ‘manus’ involving locomotion with the forelimb and an evolving flexing wrist and the ‘pes’ which refers to the hind limbs including elongation and implanting of the digits.
A) Manus B) Pes C) Wrist
Ornithodirans were evolving a middle II, III and IV tridactyl (three toes) pes elongation. Eventually, even quadruped sauropod and ornithischian dinosaurs would show a pes elongation with lengthened and symmetrical tetradactyl (four toes) plantigrade pes autopodium form, along with an asymmetrical tridactyl manus form. Birds go all the way back as the only surviving ornithodiran group.

Pes three-toed elongation
Marasuchus skeletal
Occurring 235-234 mya, Marasuchus (Mah-rah-su-cuss), formerly known as Lagosuchus was an unspecialized ornithodiran biped that was basal to dinosauromorphs. Also, Marasuchus displayed various symnapomorphies to Dinosauriformes, such as an anterior trochanter developing into a trochanter shelf.  It showed a trending in downsizing of dinosauromorphs that would extend into basal dinosaurs. At 35cm/1.2ft long, it did not have the dinosaur acetabulum (hole in hip socket) for the femur thighbone emplacement, but did share an elongate pubis and the presence of an anterior trochanter on the femur. Its forelimbs were reduced by half of the hind limb length where the hind limbs were carried close to the body’s axis. In having skull features similar to distinct pterosaur features and distinct dinosaur features, Marasuchus most likely belongs to the line where the split occurred forming the pterosaur and dinosaur lines.
Artist: KirbyniferousRegret1  Marasuchus

Marasuchus’ digitigrade bipedalism relied on a tridactyl pas elongation, even though it could move as a quadruped. This animal may also have had filamentous integuments or even proto-feathers of simple shafts which matted together in covering the body. This would suggest an insulating function, further suggesting endothermy. Both, from primitive to the most diverse pterosaurs and dinosaurs inherited these traits as we’ll soon comment on for dinosaurs later on.                          

Dinosauromorphs were more closely related to dinosaurs than to pterosaurs, but were not dinosaurs. However, they gave rise to dinosauriforms, which in turn gave rise to dinosaurs. Basic dinosauromorph osteology is that the femur head has very little offset from the shaft, in particular when compared to dinosaurs. They stood erect and moved in parasagittal fashion in swinging the limbs fore and aft as opposed to rotating them. Dinosauromorph shoulder assemblies were robust with simple and triangular hip girdles.

Dinosauromorphs showed up in the Middle Triassic ~246 mya, but in high latitudes, lived with dinosaur faunas throughout the Late Triassic for 20 million years disproving any rapid ecological displacement between the two groups.

The 235-211.9 mya dinosauromorph family, Lagerpetidae (La-grr-peat-a-day) was composed of three genera being, Lagerpeton (La-grr-pee-tun), Dromomeron (Druh-mom-rin), and Ixalerpeton (Ik-sal-ur-pee-tun). Lagerpetids were a sister group to dinosauriforms.

Artist: Apsaravis  Lagerpeton
This family group is defined by having posterior dorsal vertebrae with anteriorly-oriented neural spines, a sacrum with two vertebrae united to the ilium with a well-defined anterior projection, a wide pubis shorter than the ischium and laminar, sigmoid femur with pneumatization and a well-developed fourth trochanter without phalanges, metatarsal I short and V reduced, two distal tarsals corresponding to metatarsals III and IV with metatarsal IV longer than the rest. The acetabulum had closed with an up facing ilium; traits that would carry into dinosaur groups.

Dinosauriformes encompasses the dinosauriform as the common ancestor to all dinosaurs and dinosaurs themselves. Dinosauriforms all share shortened forelimbs, three or more sacral vertebrae, a partially to fully perforated acetabulum, an extension of femoral articular surface under the head of the femur, a cnemial (tibia/shinbone) crest on proximal tibia with the tibia also being posteriorly flanged on its distal end.

Dinosauriforms that weren’t quite a dinosaur are mostly under the family, Silesauridae (Sile-o-soar-uh-day) with the outside genus, Marasuchus (Phonetics: Mah-rah-su-cuss) as representing a sister common ancestor to the group of silesaurids. Thus far, Marasuchus is monophyletic representing no family group and has only one species in, M. lilloensis (Phonetics: M. lill-o-in-sis).

Marasuchus had no acetabulum (hip socket hole) as true dinosaurs did, but it did share an elongate pubis and an anterior trochanter on the femur. Since Marasuchus lived 235-234 mya, dinosaur evolving traits showed up during the Middle Triassic. Lightly built and small at 30-40cm/12-16in, Marasuchus was also a bipedal predator preying on small vertebrates and large invertebrates. In paving the evolutionary route, the earliest dinosaurs were also lightly built and traversed bipedally.

Since at least some early dinosaurs had primitive feathers (proto-feathers), often times Marasuchus is pictured as feathered, although there as yet has not been any definitive fossilized feathering imprints found.

The Silesauridae family, as a sister group to dinosaurians,  currently consists of six genera. They are: Lewisuchus, Asilisaurus, Eucoelophysis, Silesaurus, Sacisaurus, and Diodorus (Phonetics: Lew-iss-su-cuss, A-se-lee-sore-us, Yew-see-lo-fy-sis, Sy-el-sore-us, Sa-suh-sore-us, Dee-uh-dor-us). Pseudolagosuchus fossil remains are fragmentary and thought is trending that it is now synonymous to Lewisuchus.

All silesaurids were primarily quadrupeds and had rather long necks as compared to the torso. None most likely were direct ancestors to dinosaurs but were closely related to the ancestral link to dinosaurs. Silesaurid family members have only been discovered in the last decade.

Silesaurids were all relatively small and basically walked in a plantigrade quadruped fashion, but could rear and run bipedally if needed. Silesaurids commonly possessed a brevis shelf (muscle attachment site on ilium bone surface), a slender shafted ischium and a prominent lesser trochanter, which were all dinosaurian characteristics as well.

Although derived from carnivores, most silesaurids were herbivores, likely due to a conferred evolutionary advantage in what was going on during this portion of the Triassic when all the continents were still conjoined and Earth and life were still recovering from the mass extinction. The shift in diet of these dinosauriform ancestors to more readily available foods led to an eventual dinosaurian success.

As a family clade, silesaurids lived between 245-203 mya in the Middle and Late Triassic. Appearing 245 mya, Asilisaurus is one of the oldest known animals of the dinosaur/pterosaur avemetatarsalians. Silesaurus fossil remains are also from 245 mya, but also occurred all the way into the end of the Triassic 203 mya, well after true dinosaurs began walking the earth.

Artist: Andrey Atuchin Asilisaurus
Asilisaurus (245 mya) ~ At 1-3 m/3-10ft, this dinosauriform was a quadruped. By judging its dentition, it was also an omnivore capable of eating plants mostly, but occasionally meat. Ending in a beak-like toothless tip, the rest of the jaw teeth were triangular shaped, while large in front getting progressively smaller down the jawline. With the remains of Asilisaurus found in a Tanzanian fossil bed, including primitive crocodilians alludes to the fact that these two animal groups diversified rapidly into their respective dinosaur and crocodile lines. Asilisaurus was an herbivore and is one of the oldest archosaurs leading to the ornithosuchus line of pterodactyls, dinosaurs and birds.
Artist: Scott Reid Lewisuchus

Lewisuchus (236-234 mya) ~ At 1m/3ft, it was another quadruped that differed from other dinosauriforms in dental, vertebral and skull anatomy. Lewisuchus had pterygoid teeth, postaxial neck/trunk vertebrae with craniocaudally expanded neural spines and a dorsomedial post-temporal opening on the otoccipital portion (posterior half of the braincase in basal tetrapods) of the skull. The lower jawline dentary scheme and forelimb anatomy exhibits autapomorphic modifications related to predatory behavior. Lewisuchus was carnivorous preying on small vertebrates.
Artist: Apsaravis Silesaurus 
Silesaurus (230 mya) ~ At 2.3m/7.5ft, was also a quadruped, but due to the presence of three sacrals firmly connected to ribs and with the ilia and long tail providing a counterbalance to the body weight in front of the pelvis, suggests an ability for fast bipedal running. Although it lacked femoral and dental traits of Dinosauria members, this dinosauriform had the same characteristics of ornithischian dinosaurs in possessing the beak tip. Also, as evidenced from its bone characteristics, had a rapid maturation process, but with dense more longitudinal vascularization ceasing before reaching the peripheral avascular parallel fibered bone formed at the bone’s surface. This is an indication of a growth halt and significant decrease in the maturation ratio. The same observation is found in fossil research of all ornithischians along with most other dinosaurs. Silesaurus was herbivorous.

Artist: Apsaravis Eucoelophysis vs. Redondasaurus
Eucoelophysis (228-208 mya) ~ At 3m/10ft, was still another quadruped but with much shorter and gracile forelimbs. Originally it was considered a primitive coelo-physoid dinosaur but its hind limb anatomy negated that thought. The undeveloped posterior femoral notch and the tibia possessing a distinct appressed surface along the distal two-thirds of the bone while lacking a fibular crest, are traits too primitive to be a dinosaur. It’s now considered a sister taxon to Silesaurus. Eucoelophysis was a carnivore.

Artist: Nobu Tamaru Sacisaurus
Sacisaurus (225 mya) ~ At 1.5m/4.9ft, its osteology was very similar to ornithischian dinosaurs. There is a process at the tip of the mouth resembling the ornithischian predentary bone. With teeth no longer than 3mm/0.12in this dinosauriform could not adequately defend itself with biting teeth. However, the teeth were excellent for processing plant material. The legs were long in proportion to body length indicating an ability for speed in running. Sacisaurus was an herbivore.
Artist: Scott Reid Diodorus
Diodorus (216 mya) ~ At < 1m/3.3ft, it had forward canted teeth that decreased in size toward the anterior end of the lower jaw. Also with smaller teeth, there was a distinct lateral ridge running parallel to the dentary alveolar margin. Diodorus is considered as the sister taxon to Sacisaurus. The Diodorus taxon provides further evidence of a near-cosmopolitan range for basal dinosauriforms in the Late Triassic and further demonstrates the disparity of dental morphologies getting smaller within Silesauridae. Diodorus was herbivorous.

Dinosauriforms had set the stage for true dinosaur evolvement as their fossil finds throughout the globe are evidence of a near-cosmopolitan range for dinosaurs to thrive in by taking advantage of natural selective biomes, ecologies and environments. 

The first of true, but primitive dinosaurs to appear were around 243 mya, moving the dinosaur lineage back another 13 million years than what was previously thought. So we cannot think that dinosaurs were a homogenous pot occurring as all together during a certain period. When dinosaurs first appeared, they did not facilitate a rapid takeover in out-competing other species in hastening their extinction. Dinosaurs lived side by side among other animal species groups, such as crocodilians, synapsids, sphenodonts, Rauisuchus, rhynchosaurs, pterosaurs dinosauromorphs and dinosauriforms.

In fact, from a 230 mya swamp fossil bed, embedded in its rock, were remains of the basal sauropod dinosaur, Buriolestes alongside the dinosauromorph, Ixalerpeton and numerous other animal groups.

Artist: Maurílio Oliveira
In the illustration above, it includes: Buriolestes climbing over the fallen tree trunk with six others behind it, seven Ixalerpeton in the lower left corner, an aetosaur in the lower right corner, a small rauisuchian to the right center, a sphenodont on the tree and a yellow amphibian entering the water in the right-center.

The shared anatomical features of dinosaurs are:
1)    A supratemporal fossa (skull excavation).
2)    An epipophyses present in the anterior neck vertebrae behind atlas and axis.
3)    Radius (a lower arm bone) 80% shorter than humerus bone length.
4)    Femur's (thighbone) fourth trochanter is a sharp flange.
5)    4th trochanter asymmetrical with distal lower margin forming a steeper angle to shaft.
6)    Exoccipitals (bones at the back of the skull) do not meet along the midline on the floor of the endocranial cavity as in former archosaurs.
7)    Proximal articular surfaces of the ischium with the ilium and the pubis are separated by a large concave surface.
8)    Upper ankle bones and the proximal articular facet (connecting surface for fibula) occupy < 30% space of the transverse width of the element.
9)    The pelvis proximal articular surfaces of the ischium, ilium and pubis are separated by a large concave surface.
10) Tibia’s cnemial crest arcs anterolaterally.
     11) Distinct vertical oriented ridge on posterior face of tibia’s distal end.
     12) Top surface of the calcaneum where adjoined to fibula has a hollow profile.

As well, Dinosauria are now considered monophyletic due to numerous autapomorphies including: elongate vomers, three or more sacral vertebrae, three or fewer phalanges on fourth digit of manus, grasping hand produced by a thumb that could bend inward (bending occurs at joint between metacarpal I and first thumb phalange), fully offset (inturned) proximal head of femur with a distinct neck and ball, greatly reduced fibula, well-developed ascending process of astragalus, upright posture and a digitigrade stance.

Traditionally, dinosaurs have been divided into two subgroups known as, Ornithischia (Or-nee-this-key-uh) and, Saurischia (Sawr-is-key-uh). The two clades’ main dinosaurian differences are in the hip joints, where ornithischians’ pelvis is bird-like, while the saurischian pelvis is lizard-like. Ornithischia is Greek and actually means bird hipped, where, Saurischia in Greek means lizard hipped. Saurischia is further divided into two subgroups being, Theropoda and Sauropoda. This all has to do with the positioning of the pelvic bones, the ilium, ischium and pubis. Ornithischians’ pelvis is more situated as birds, while saurischians have the three bones positioned more like lizards. The bird hip is considered an ‘opisthopubic’ pelvis, where, as in birds, the pubic bone extends back towards the tail of the animal. A lizard hip is a ‘prepubic’ pelvis where the pubic bone extends forward towards the animal’s head. This is where I want to chime in on a thought before we go any further.

Above are the familiar dinosaur hip illustrations we’re all familiar with. As but a young fella, I’ve always wondered how theropods, which indeed were lizard hipped saurischians could have evolved into birds when it was ornithischians that had the bird hipped arrangement. Well, it appears that finally paleontologists are beginning to figure this out.

Above is a new cladogram devised by Ph.D. Baron Matthew when he was a doctorate student at the ‘University of Cambridge’. In the illustration, are the phylogenetic relationships of early dinosaurs through a time-calibrated strict consensus of 94 trees from an analysis with 73 taxa and 457 characters. A – Is the least inclusive Dinosauria clade that includes Passer domesticus, Triceratops horridus and Diplodocus carnegii. B – Is the least inclusive clade of Ornithoscelida (Phonetics: Or-nee-tha-o-sell-lee-duh) that includes P. domesticus and T. horridus. C – Is the most inclusive Saurischia clade that contains D. carnegii, but not T. horridus.

The cladogram further illustrates all subdivisions of the time periods (white and grey bands) are scaled according to their relative lengths with the exception of the Olenekian (Early Triassic), which has been expanded relative to the other subdivisions to better show the resolution within Silesauridae and among other non-dinosaurian dinosauromorphs.

What this tells us is that as more dinosaur discoveries are being made, phylogenic and anatomical relationships have made us realize that the simple hip bone categories are no longer adequate enough to separate dinosaurian relationships. The traditional bird-hip/lizard-hip relationship is no longer adequate in the thinking that ornithischians and saurischians came from separate ancestors. Now we know that dinosaurs all evolved from a common ancestor.

However, in more ways than one ornithischians are anatomically more similar to theropods than theropods are to sauropods. Further, in coming from the same clade, ornithischians and theropods both had the same potential to develop bird-hip anatomies; it’s just that the ornithischians did it first, before theropods hit the genetic switch when they began evolving into birds. This revised clade grouping of ornithischians and theropods is a revival of the name, Ornithoscelida, originally coined by evolutionary biologist, Thomas H. Huxley in 1870. In this scheme, herrerasaurids as a basal sister group to sauropods, are both grouped under Saurischia. This makes sauropods the least related dinosaur to ornithischians and theropods. Sauropods simply retained their ancestral archosaur reptilian pelvic arrangements. Also, this cladogram firmly attaches theropods as the basal common ancestry to all birds extant and extinct.

Please keep this in mind, for it may not yet be consensus, but as the majority of paleontologists have the Baron cladogram in waiting for more review, soon I feel, it most certainly will be the new dinosaur clade. Although this Baron et al grouping only uses species level operational taxonomic units (OTU) that enlists metagenomics in utilizing similar sequence variants, which in itself has a few limits in distinguishing at the species level, I will be introducing dinosaur clades under the new Ornithoscelida clade scheme instead of the older current ones.
- Out with the old cladistics and in with the new -
The early dinosaurs, as exposed from fossil findings, had a large variation which most likely allowed higher successful rates in harsh environmental conditions that the Triassic offered. One main variation was growth rates within species. From ontogenetic sequence analyses, early dinosaurs had a much higher level of growth patterns than did the other reptile groups at the time. In addition to possessing different growth pathways from hatchling to adult, there too, was a large amount of size variation within species like a younger adult individual being much bigger than an older individual. This is the same biological strategies humans possess as well, for in any community you will find much taller teenagers compared to grown adults.

As a result, when the Triassic/Jurassic extinction occurred, the species and individuals of species with the most variants to withstand the harsh environmental conditions managed to survive and those that didn’t, succumbed. Except for crocodilians and dinosaurs, all archosaurs went extinct at the Triassic/Jurassic border. Other groups also perished as displayed in the extinction graph below.

Triassic/Jurassic Extinction
An interesting basal archosauriform that didn’t make it past the extinction event was Vancleavea (Phonetics: Van-cleve-uh). At 1.2m/3.9ft log, it was semiaquatic and had a tail deepened by elongated osteoderms as opposed to tall neural spines that was normal in all other aquatic tetrapod groups. Two other unusual traits were imbricating osteoderms covering the entire body and the jaws were lined with enlarged caninform teeth (non-mammalian animals that possess dog-like canines) that protruded from the mouth.

Artist: Smokeybjb Vancleavea
One dinosaur that took variant evolvement in its own life stages to the extreme was Limusaurus (Li-mu-sawr-us). Living 160 mya, if only one or two fossils had been found we’d never know its ecological adaptions, but since nineteen individuals have been found representing separate age groups, we know its full life history.

Artist: Yu Chen  Limusaurus

Limusaurus, a biped stood at 1.5m/4.9ft when fully grown. Limusaurs came into the world with a full set of firmly rooted carnivorous teeth, but as it aged it lost all of its teeth as they were replaced with an herbivorous beak in adulthood. As yearlings, limusaurs were fully carnivorous going into the subadult stage. At one year it began losing back teeth foregoing carnivory for an omnivorous diet until reaching adulthood. As an adult, all teeth were replaced by a beak in favoring an fully herbivorous diet.

Apparently this kept competition at bay when it came to food resources between the young and adult limusaurs. To accommodate the diet transitions, proportions of the skull and upper jawbone configuration began to modify in a pronounced downward curve to develop the exterior beak. The larger adult individuals swallowed stones to aid the gizzard in grinding vegetative food, whereas the carnivorous young did not.

Newer speciation arose from within a species through vicariant speciation which is allopatric (geographic speciation). This form of speciation emanates when biological species become isolated through geographical means. A classic example is in the theropod family of carcharodontosaurids.

Artist: Dinoraul Acrocanthrsaurus
In the Early Cretaceous, Acrocanthosaurus (Ack-row-can-fo-sore-us) showed up around 116 mya. At that time, the world’s landmasses were still enough connected allowing for transcontinental dispersal. Acrocanthosaurs originated in what is now the central southern portion of the U.S. in Texas and Oklahoma. This dinosaur spread throughout what is now South America and Africa. By the Late Cretaceous land bridges intra landmass contacts had been taken over by the oceans and the further continental spreading.

Artist: Willydynamo55 Giganotosaurus vs. Macrogrypgosaurus

This isolated acrocanthosaur populations in varying ecological environs of the forming continents, to the point the South America population of Argentina developed enough genetic variation to become the new genus, Giganotosaurus (Gye-guh-nuh-tah-sore-us) as the result 98-97mya. The same happened in the North African population forming the genus, Carcharodontosaurus (Car-kah-roe-don-to sore-us) 112-93.5 mya. The ecological isolation further affected size, with Arcocanthosaurus at 11.5m-38ft, Giganotosaurus at 12.5m/41ft and Carcharodontosaurus at ~ 13.3m-44ft.

Credit:BBC Carcharodontosaurus

Like pterosaurs, skeletal pneumaticity was found in dinosaur fossils. Functions of skeletal pneumatics include weight reduction in large-bodied or flying dinosaur taxa and density reduction resulting in energetic savings during foraging and locomotion. The pneumatic system is comprised mostly of the lung. Indeed, all the little pockets that arise come from expansions of the primary bronchus, a tissue that surrounds the lung itself. It is this tissue forming the little sacs. This is known as the ‘pneumatic diverticulae’ that ends up throughout the body as well as inside the bones.

Though evidence is lacking in caudal pneumaticity in sauropod fossil finds, it is quite evident in the rest of the vertebral column. Also, in all sauropods, air-filled hollow bones were throughout the postcranial and anterior body. Like dinosaurs’ nearest surviving relatives of crocodilians and birds, sauropods did not have a diaphragm, so the dead-space volume of a 30-ton sauropod would be about 184 liters of air. This is the total volume of the mouth, trachea and air tubes. If the animal exhales less than this, stale air is not expelled and is sucked back into the lungs on the following inhalation. This is how we know that sauropods relied on respiratory pneumatics to properly inhale and exhale.

Pneumaticity of the cervical and anterior dorsal vertebrae occurred early in theropod evolution. Although not pinpointed, evidence shows that only some of the theropod thoracic air sacs were present as plesiomorphic, but then modified and embellished on by each theropod clade separately. The acquisition of extensive postcranial pneumaticity in small-bodied maniraptorans (clade consisting of birds and non-avian dinosaurs) makes avian-like high performance endothermy a good sequel. Oviraptorids (bird-like, herbivorous and omnivorous maniraptoran dinosaurs) showed an astounding number of skeletal air sacs and postcranial pneumaticity sites.

Flow through ventilation first occurred in theropods. Due to an incredibly preserved Upper Cretaceous ‘Maevarano Formation’ fossil find of Majungasaurus (Muh-jung-ah-sawr-us) in NW Madagascar, the series of vertebrae and portions of the ribs preserved pneumatic foramina (cavities) that may have resulted from the infiltration of avian-style lungs and air sacs. This would have been a basic ‘flow through ventilation’ system where air flow through the lungs is one-way allowing oxygen-rich air inhaled from outside the body to never be mixed with exhaled air laden with carbon dioxide. This is the same breathing system birds of today extol and although it’s complex, it is highly efficient. Majungasaurus roamed 70-66 mya.

Carcharodontosaurus, mentioned earlier above, utilized ‘flow through ventilation’ to the maximum in efficiency by employing a row of pneumatic air sacs so devised that it ensured a continuous and constant flow of oxygen be supplied to and through the lungs during respiration. This gave this dinosaur a huge advantage over its fastest prey, as it could easily outrun them. It also complimented its hunting style, which was viper like to strike and recoil, then wait for the wounded prey to die. Carcharodontosaurs, with large forelimb claws or a quick bite, would lacerate or slice its shark-like serrated teeth into a vulnerable area, wait out for the mortal wound to take effect then begin feeding on the dead prey. This strategy saved this carnivorous theropod from any injuries that might occur during battle with a struggling prey that might have had its own weaponry of defenses. 

However, concerning ornithischians, there has thus far been no evidence of skeletal pneumaticity found in their dense bones. Perhaps they had developed intricate lungs for air capacity or soft tissue air sacs that wouldn’t fossilize. Ornithischians show an evolving reduction in skull pneumaticity with the closing of the antorbital cavity. Reasons for this could be as the feeding skull components expanded phylogenetically, the antorbital cavity contracted. Or simply, weaker point skull pneumaticity gave way as bonier head components and increased body weight arose for defense.   
As far as intelligence goes dinosaurs were not the lumbering dimwitted nitwits we once thought they were. All dinosaurs could be quick reacting under stressful situations, even mental reasoning to cause and effect. One really stands out when it comes to intellect and judgment. Occurring 77.5-76.4 mya, Troodon (Tru-o-don) was perhaps the most intelligently derived dinosaur thus far discovered. Its cerebrum to brain ratio was up to 63% higher than other non-avian theropods. The brain itself as compared to body size was much larger than extant reptiles and most probably possessed the same measured intelligence as most birds.

Mugger crocodile using sticks as tools for bait

We don’t know if dinosaurs used simple tools as today’s American alligator or mugger crocodile does in stacking sticks on top of its snout to entice then snare breeding shorebirds, but Troodon certainly had the intelligence to do so.    

In diet, most of the earliest dinosaurs were insectivores and carnivores, with a few omnivorous species and very little herbivores. Of course once into the Jurassic in kicking off their reign, dinosaurs covered every base in being insectivores, herbivores, carnivores, scavengers and even with spinosaurs, became semiaquatic piscivores.

Even cannibalism is evident in, Majungasaurus. Unlike carcharodontosaurs, majungasaurs with strong jaws and a wide bite filled with gripping teeth, would hold prey with the bite. With the exacting majungasaur teeth marks found in the fossils of other majungasaurs, we know it cannibalized, but we don’t know the reasons why. Prey scarcity due to changing environmental conditions could’ve made it desperate for food or it could’ve come upon an already rotting dead majungasaur carcass. Thus far though, Majungasaurus is the only genus of dinosaur found to eat its own kind.

All carnivorous theropods would tear off chunks or strips of flesh from their prey and swallow it whole. Primitive ornithomimosaurs and oviraptorosaurs evolved from carnivorous theropods, but with weak jaws and small dulled teeth probably were omnivorous.

Artist: Damir Martin Therizenosaurus herbivorous family

One group of theropods that did evolve from a flesh eating carnivore into a plant eating herbivore was in the family, Therizenosauridae (Phonetics: Thu-rise-zen-o-sawr-ah-day) with species living 94-66 mya. These were large theropods that reached up to 10m/33ft in length. With very broad bodies and long necks standing on weight bearing hind limbs supported by four weight bearing toes, was an unusual evolvement from its contemporary theropods that walked on three toes with the fourth representing a dew claw.

Even though this has occurred throughout the course of Earth’s biological history, such as hominids going from a strictly herbivore diet to an omnivore one, or even a fully carnivore one as some West Texas cattle ranchers would like to attest to, for a flesh eating theropod converting over to a plant diet is unusual upon itself in the body accommodating the transitioned diet.

Therizenosaur manus claws

But what made therizenosaurs even more remarkable from other theropods with normally short forelimbs was in the size of their three forelimb claws ending on rather long arms. At just under 1m/2.2ft, therizenosaurs had the longest claws of any known animal extinct or extant. In being considered a top contender for the emergence of an herbivory lifestyle within Theropoda, therizenosaurs had short, but packed serrated teeth for slicing and chewing in a small mouth. With the theropod defense gone in its biting abilities, therizenosaurs evolved and developed the large claws ending on robust and long arms for defense, although the longer arms and claws may have originally evolved to reach for higher limbs, clamp onto them and bring them down towards the mouth. Just as in venomous snakes, where the toxin from modified salivary glands was first developed for capturing prey and as a secondary element for defense, so too might have been the therizenosaur forelimbs.

In jumping ahead here, as this bit of info should be addressed later on under the bird section, but in considering therizenosaurs’ evolvement into herbivores; due to their theropod anatomy, certain morphologies evolved that may have started the trend towards theropod birdom. A keratinous beak tipped rostrum was developed to enhance cranial stability by mitigating the stresses and strains of chewing in pre-processing vegetation material and cellulose. For a more adaptable upright reach, the pectoral girdle was modified to augment longer reaches. Therizenosaurs also evolved an opisthopubic pelvis (pubic bone extends posteriorly) much like ornithischians and birds. This was done to enhance the weight bearing hind limbs. But most of all, (although not for flight, instead, for thermoregulation and courtship), therizenosaurs are one of the first animals to produce bird-like feathers; albeit primitive feathers considered as stage-1where the feathering was spine-like. The latter more evolved therizenosaurs possessed stage-3 serially fused feathering barbs.                  

Herbivore dinosaurs had jaws that only slightly opened and closed where all the teeth met to masticate the food, except for sauropods; they only had teeth suitable for stripping food items from plants then swallowing it whole relying on large abdomens equipped with gastroliths (swallowed stones) to grind and bacteria to aid in the digestion of cellulose. Other herbivores like most ornithopods had no teeth but were equipped with horny beaks to snip off food items then swallow it whole and allow the digestive tract similar to sauropods to break down food tissue. With no large stomachs to accommodate vegetative materials, the beaked ornithopods, such as hadrosaurs had beaks for snipping and weak jaws and teeth for grasping, but not for chewing. They most likely ate fruits and softer plant materials not requiring an elaborate digestion tract.

Chilesaurus skeleton

Chilesaurus jaw and teeth
One dinosaur that lived 145 mya measuring 3.2m/10.5ft was, Chilesaurus (Chill-a-sawr-us) that had an array of theropod coelurosaurian and basal ornithiscian and sauropodomorph traits. Currently there is a trend to pull it from the rank of theropod to ornithischian, but regardless, it is going to be nestled snug right between them as an herbivorous ornithoscelidan. The teeth are very unique in being leaf shaped that are elongated and point forward. With ornithiscian similarities, it had a beak and the pubis bone was pointed posteriorly as ornithiscian bird hips do to make room for a larger gut as witnessed in sauropods while all this was supported by a theropod skeletal anatomy.
Artist: Gabriel Lio Chilesaurus

During their reign, large carnivorous dinosaurs ate pretty much any other animal during their dominance in the Jurassic and Cretaceous, but any of them could have also been prey by being on other carnivorous animal’s menu.

Artist: Fabio Manucci Razandrongobe

During the Jurassic lived, the oldest known notosuchian, Razanandrongobe (Ray-zah-non-dron-goab), a crocodyliform living 167-164 mya. It possessed teeth larger than any predator dinosaur of the day and were used for crushing bone. It was an apex predator that could subdue any dinosaur during its time.

Artist: Sergey Krasovskiy Beelzebufo

Other animal predators that ate dinosaurs were crocodylians, pterosaurs and even a particularly large toad known as, Beelzebufo (Be-l-zah-buff-fo) could easily have handled many types of baby dinosaurs.
Artist:Anna Kocheva Hatzegopteryx 

Artist: Mark Witton Hatzegopteryx

The pterosaur, Hatzegopteryx (Hat-zee-gop-ter-ix) also must’ve dined on dinosaurs. Isolated islands make large species shrink in size and small species enlarge in size. This phenomenon is called the ‘island rule’. During the Cretaceous, there existed small European subtropical islands during the break up of Pangea within the Tethys Sea. These islands had animal populations separated from their mainland kin. The sauropod, Titanosaurus (Tie-Tan-o-sawr-us) was large on the mainland grounds measuring up to 12m/40ft. Isolated from the mainland on one particular island called, Hateg Island that is now a part of Romania, titanosaurs experienced insular dwarfism cutting their size in half to no more than 6m/20ft. Their young weren’t even half that size. In fact the island titanosaurs were so miniature in size as compared to mainland titanosaurs that they’ve been assigned another genus, Magyarosaurus (Mag-yar-o-sawr-us).  Hatzegopteryx would soar from the main lands to the island where the magyarosaur young were easy pickings. Hatzegopteryx would also prey on other dinosaurs small enough to catch and swallow in one gulp.

Artist: Robert Nicholls Deinosuchus
Artist: Josh Cotton (greeni-studio) Deinosuchus
Then of course there were the large crocodilians like the 10.6m/35ft alligator, Deinosuchus (Die-no-su-cuss) that took their toll on possibly even the larger theropods.

Artist: James Guerney Repenomamus

Even mammals of the day took their share of small dinos. Living 125-123.2 mya, Repenomamus it is the largest Mesozoic mammal known at 1m-3.3ft long. It was carnivorous and at one of its fossil finds in the ‘Yixian Formation’ of China were the remains of a young Psittacosaurus in its stomach.

Repenomamus fossil with Psittacosaurus remains
Dinosaurs roamed throughout the Jurassic and Cretaceous world topographies. Fossils have been discovered in lowlands, highlands, deserts, forests, tropical climes and cold climes in both the Arctic and Antarctic. During Cretaceous ice free summers, the earth poles experienced only intermittent sea ice throughout the rest of the year. Average pole temps were 10 °C/18 °F because there was much higher concentrations of CO2 in the atmosphere at 1000 ppm…two and a quarter times than currently, even though today’s atmospheric CO2 saturation levels are alarmingly increasing. Even though in today’s arctic temperatures, 10 °C/18 °F would be mild weather that range for a reptile is still cold. Most extant ectothermic reptiles cannot tolerate higher latitude arctic conditions as their survival is dependent on ambient temperatures.

Let’s get reacquainted with organism body regulations:
§  Poikilothermy ~ internal body temperature highly varies
§  Homeothermy ~ maintaining a stable internal body temperature regardless of external influence
§  Stenothermy ~ survival only within a narrow temperature range
§  Eurythermy ~ can function at a wide range of different body temperatures
§  Ectothermy ~ relying almost purely on ambient heat
§  Endothermy ~ heat set free by internal bodily functions

So for dinosaurs to have existed in cold environments, they could not have been poikilothermic/stenothermic. Dinosaurs that inhabited the pole regions were either homeothermic/stenothermic, or endothermic/eurythermic, or at least be poikilothermic/ectothermic as the mammalian naked mole rat is today.

Fossilized Haversian canals 

Also, we now realize dinosaurs weren’t as cumbersome and sluggish as an ectotherm (cold blooded) would be. Dinosaurs were very active and agile with higher metabolic rates than an ectotherm would be. The reasons we now feel dinosaurs were endothermic (warm blooded) is for one, their bones possessed Haversian canals which are a series of microscopic tubes containing capillaries and nerve fibers. The bones possessing the canals are called cortical bone with the Haversian canaling occurring in the outermost region of the bone. The only animals we know of that also possess Haversian bone are mammals and birds, in which both are endothermic.

Dinosaurs lived and died near both poles enduring not only the cold, but endless winter days of no sunlight. A hadrosaur fossil find of Edmontosaurus (Ed-mon-toe-sawr-us) was discovered near the North Pole. In other fossil finds, there was the discovery of a new hadrosaur species, Ugrunaalluk kuukpikensis, meaning ‘ancient grazer in Inupiat Eskimo. With other hadrosaurs, pachycephalosaurs and thescelosaurs fossils, there were also the carnivorous dromaeosaurs, gorgosaurs and troodontids. The Alaskan troodons were much larger than their more southern counterparts.

Artist: Maija Karala Ugrunaaluk

Among the polar fossil finds are remains of fern, cycad, conifers and pollen from shrubs and herbs. This was truly a self-sustaining biodiversity. All the fossils were found in the 70 million-year-old ‘Lipscomb’ fossil bed that is a part of the 80-60 mya Prince Creek Formation, made up of alluvial deposition layered on top by mud flats. These mud flats give evidence of multiple dinosaur tramples alluding to herding.

Down at the other end of Earth in what is now the Antarctic, from Cretaceous rock oxygen isotope levels, the estimated mean annual temperatures were between 0 and 8 °C/32 and 46 °F. Fairly warm for today’s Antarctic subzero temperatures but still cold for what we think dinosaurs could thrive in. Rocks the dinosaur fossils were found, in an area called ‘Dinosaur Cove’ give evidence of permafrost from features such as ice wedging and hummock ground. Permafrost normally occurs in temperature ranges of between −2 and 3 °C/28 and 37 °F. Also, there were indeed long wintry polar nights with periods of up to six months of total darkness, although there is no evidence of a polar ice cap. The Antarctic floral community at this period consisted of forests of conifers, ginkgoes, ferns, cycads, bryophytes, horsetails and even a few flowering plants.

In the Early Cretaceous, East Gondwana was composed of Antarctica still linked to Australia after both had rifted and drifted from Africa. Much of East Gondwana’s southern portion at the time laid inside the Arctic Circle. It is in this region where most of the Antarctic and Australian dinosaur fossils are found. By the end of the Cretaceous, Australia had fully rifted apart from Antarctica moving further away from the South Pole and Antarctic Circle, taking away any land bridge. This separated the Antarctic and Australian dinosaur species from their respective kin, which then evolved into differing genera.

Antarctica had six genera of dinosaur with four herbivores in the ankylosaur Antarctopelta (An-tarc-toe-pel-tah) and the three ornithopods,  Atlascopcosaurus (At-lass-cop-ko-sawr-us, Morrosaurus  (Moe-row-sawr-us) and Trinisaura (Tree-nee-sore-rah);  one omnivore in, Glacialisaurus (Glay-see-al-ee-sore-us) and one carnivore in, Cryolophosaurus (Cry-oh-low-foe-sawr-us). For the Australian portion that was once a part of Antarctica, nineteen genera fossils have been discovered.

Artist: Solec Kujawski Atlascopcosaurus

Of the Antarctica dinosaurs, the basal ornithopod, Atlascopcosaurus showed up 114 mya in the Early Cretaceous. It was ~ 2-3m/6.5-10ft long and most likely, as other iguanodontids was horn beaked and could move either on the two longer hind limbs or on all fours. On an interesting note, this is the only dinosaur to be named after the Swedish corporation, ‘Atlas Copco’ who manufactures construction and mining equipment and also assisted in the excavation of the fossil remains.

Artist: Mike Belknap Antarctopelta
As a herbivorous quadruped, the nodosaurid, Antarctopelta occurred in Antarctica during the Late Cretaceous 74-70 mya. At 4m/13ft, it had osteoderms (armored bony plates embedded into the skin with shoulder and neck spikes and a short spike extending from the supraorbital bone that pointed outwards from below the eyes.
Artist: Sebas Runa Morrosaurus

Artist: Peter Trusler Trinisaura as the cold caught up
Morrosaurus (~70-69 mya) and Trinisaura (80-66 mya) are also two ornithopods that showed up in the Late Cretaceous. Morrosaurus was no more than 2.5m/8.2ft, while Trinisaura was ~ 1.5m/4.9ft in length. As an ornithopod, both Morrosaurus and Trinisaura belonged to the newly evolved Gondwana clad, Elasmaria (Ell-as-mah-ree-uh). This clad was characterized by tightly fitted foot bones, chevrons (a series of ventral caudal bones to protect tail nerves and blood vessels), and a narrow foot with a thin fourth metatarsal with all traits indicating a speedy gait and running lifestyle. Later Australian clad members also featured thin plates within the thorax, which were discs of mineralized intercostal cartilage between the ribs. It appears that as being basal, the two Antarctic genera, Morrosaurus and Trinisaura had not yet developed the thorax plates. The word, Elasmaria is Greek in reference to ‘thin plate’.

Artist: Peter Trusler Glacialisaurus eating from tree
From the Early Jurassic, Glacialisaurus lived 189-183 mya when Antarctica and Australia were conjoined further north of the Arctic Circle and still interlocked to Africa and South America. At no more than 7m/23ft long, Glacialisaurus was a sauropodomorph and not a true sauropod. But it lived beside them as the earliest sauropods have been found in the same formation Glacialisaurus’ remains were excavated from in the tuffaceous siltstones and mudstones of the lower part of the Hanson Formation, on Mount Kirkpatrick. Glacialisaurus was an advanced sauropodomorph that had a long hefty neck and could walk bipedally. The hind limbs ended in toes that were angled as opposed to sauropods where the toes were vertically shafted. In other words, in sauropods, the digits were bound forming a pseudo hoofed pad, whereas in Glacialisaurus the toes and fingers were free. The digits were distinct and the forelimbs had extended metacarpals that could grasp. In fact, Glacialisaurus had the ability to climb low objects like a fallen tree or low lying rock; in particular the young. The large powerful hands ending in claws suggest that it was an omnivore.

Cryolophosaurus skeletal anatomy
Artist: Joe Tucciarone Cryolophosaurus
194-188 mya in the Early Jurassic, Cryolophosaurus roamed the Antarctic. The fossils remains give a length of 6.5m/21ft when the carnivore was alive. This dinosaur is colloquially called, ‘Elvisaurus’ due to a crest that ridged from the front of the snout then rising from atop the head just behind the snout. The nickname is owed due to the crest resembling the pompadour hairstyle of Elvis Presley. In the young and adult stage, there are two growing crests that eventually fused into one in the adult stage.  Through the theropod bird snout clad of Averostra (Av-ris-tra), as a sister group to the family Dilophosauridae, ‘Elvisaurus’ was closely related to Dilophosaurus (Di-loff-o-sawr-us), which had two distinct crests running up and down the top of the snout. These crests were fragile so most likely were used in mating purposes.

Artist: Fabio Pastori Lft:Cryolophosaurus Rt:Dilophosaurus

Besides chasing down herbivorous dinosaurs, we also know Cryolophosaurus dined on other animals, as the mammal-like reptile cynodont, tritylodont’s teeth were found in the gut cavity of Cryolophosaurus’ fossil remains. But also, the remains showed tooth marks randomly put of other smaller theropods that most likely were consuming Cryolophosaurus’ carcass.                 

Dinosaur Clades:
There is a world of dinosaurs and to go over each one would require an exposé in encyclopedic form. Just in sauropods alone there are over 120 known species. So what we’re going to do is discuss sauropods, ornithischians and theropods in the respective group levels finishing with the theropod lead-in into birds.

Simplified cladogram on the path to dinosaurs

All dinosaur lineages evolved from within a single group of archosaurs such as the proterosuchids and Euparkia, which was elaborated on under the pterosaurs of ‘Et Tunc Nulla Erat VII’. Even though dinosaur radiation included carnivorous bipeds and herbivorous quadrupeds, they all arose from bipedal omnivores with long grasping hands such as Nyasasaurus (243mya), and herrerasaurs 230-220 (mya).

Just a reminder...all sauropods are sauropodomorphs, but not all sauropodomorphs are sauropods. This is the case for any infra ordering of related species as the refinement of clans become more specific. To bring this to terms in thinking about it, all Homo species are primates, but not all primates are Homo species.

Sauropodomorpha Clade
Sauropodomorphs are the long necked herbivorous dinosaurs that existed from the Late Triassic to the Late Cretaceous 231.4-66 mya. The long necks fit an eating niche in accommodating greater access to higher up tree limbs. They became the dominant herbivore before the end of the Triassic and managed to survive the extinction events between the Triassic/Jurassic boundary and the Jurassic/Cretaceous boundary. For the most part, except for the earliest species, they were quadrupeds. The latter forms developed a four legged graviportal (slow moving over terrain) gait due to their heavier size and length. 
Artist: Nobu Tamura Saturnalia

Although smaller at first, sauropodomorphs later became the largest terrain animals to ever walk the earth. Of 228 mya, Saturnalia (Phonetics: Sah-tur-nay-lee-uh) was only 1.5m/5ft long while the massive Argentinosaurus (Ar-jen-teen-oh-sawr-us) was 35m/115ft that could tremble the ground on every step 97-93.5 mya. Although only an estimate, due to lack of fuller fossil material, the argentinosaur species, Argentinosaurus huinculensis may have reached a length of 39.7m/130ft. Sauroposeidon (Sawr-o-pss-sy-don) from 120 mya was probably the tallest, reaching about 18m/60ft high. Reaching extremities in size was a natural selection sequence for defense, for other than size they only had weak teeth and a retained thumb with a claw on their forelimbs for defense.

The teeth, shaped like spoons weren’t even efficient for masticating food, so the swallowing of stones (gastroliths) for grinding and relying on bacteria to break down the nutrients evolved within the sauropodomorph’s digestive strategies. They also possessed large nares (nostrils) and had 25 presacral vertebrae just like in most humans that have 23-25 presacral vertebrae.
Artist: Cisiopurple  Sauropodomorphs

The most derived sauropodomorph discovered thus far is, Panphagia (Pan-fah-eg-ah) and Chromogisaurus (Kro-mo-ge-sawr-us) that lived 230+ mya. Panphagia was a mere 1.3m/4.3ft while bigger, but still really small for sauropods, Chromogisaurus was 2m/6.7ft. Both were bipedal and in the process of transitioning from carnivores to sauropod herbivores, these sauropodomorphs were omnivores and insectivorous. All primitive and basal sauropodomorphs went extinct after the Triassic/Jurassic extinction.
Lft ~ Artist: Nobu Tamura Panphagia Rt ~ Artist: Cisiopurple Chromogisaurus  

Herrerasauridae Cladogram

Some of the earliest dinosaurs come from the family Herrerasauridae (Phonetics: Huh-reah-ruh-soar-uh-day). Herrerasaurid dinosaurs like the Late Triassic, 235-228 mya, Caseosaurus (Kay-see-o-sawr-us) and the 235-210 mya, Chindesaurus (Chin-dee-sawr-us) carried anatomy traits possessed by all three dinosaur subgroups making them very difficult to classify in whether belonging to theropods, ornithischians or sauropods. All herrerasaurids were bipedal carnivores. The ~231.4 mya, Herrerasaurus (Huh-reah-ruh-sawr-us) possessed derived archosaur traits, but also basal dinosaur traits. As a basal trait, the ilium was supported by just two sacrals, while as a derived trait, its pubis pointed backwards.

Credit: UK Nat'rl His. Museum Chindesaurus 

Artist: Mark Hallett Staurikosaurus
Artist: Gonzalezaurus Sanjuansaurus
Even though herrerasaurs carried particular traits witnessed in all three dinosaur subgroups, the new phylogenetic Baron cladogram has grouped herrerasaurids in with sauropods. In speculating, I’ll give a few reasons why for that affinity. It had a long tail and small head supported by a narrow skull resembling the primitive archosaur Euparkeria (U-par-care-ee-uh). Sauropods are known for small heads as compared to their large bodies. In the manus and pes of the herrerasaurs’ limbs, the carpus was composed of four distal carpals, while in the makeup of early sauropodomorphs, although reduced, there were three distal carpals present that articulated with the proximal ends of metacarpals (digits) I, II and III. Early sauropods continued this trait with three laterally reduction carpals. Also, the thumb was curved upwards as earlier sauropods would present it negating it as weight bearing. Although shorter than the hind limbs, herrerasaurid forelimbs were relatively long and could have been used in a quadruped stance.

Artist: Apsaravis 2 Herrerasaurus & a rauisuchian

Three herrerasaurids in, Herrerasaurus, Sanjuansaurus (San-wan-sawr-us) and Staurikosaurus (Store-ick-o-sawr-us) are relegated as a node clad polytomy group, meaning more than two descendants are involved within a cladogram and in this herrerasaurid case, placed outside of saurischian’s direct taxonomic ancestry. But, these three herrerasaurids are still listed as the most primitive group of Sauropoda.

Artist: Julius T. Csotonyi Aardonyx

A 190 mya Early Jurassic sauropodomorph showing the evolutionary transition into sauropods was, Aardonyx (Ard-o-nix). Representing the transition from biped sauropodomorphs to quadruped sauropods, it was bipedal itself, but could easily walk as a quadruped. With the pelvic girdle and hind limb structuring, it was a biped, but with stiffening rigidity taking over flexibility in the forelimbs, it was trending towards a quadruped weight bearing form.
Artist: Heidi Richter Massospondylus

One of the oldest dinosaur fossil embryo is from the 4m/13ft in length sauropodomorph, Massospondylus from the Early Jurassic 200-183 mya. The 190 mya fossil embryos were from a nest site in what is now South Africa. The developed and well preserved embryos were still in the eggshells and at birth would’ve only been 20.3cm/8in long.    
Artist: Julius T. Csotonyi Massospondylus

As a subgroup to sauropodomorphs, sauropods are the giants we immediately think of when contemplating dinosaurs. All sauropods were herbivores and developing their digestive strategies as explained previously, they required heavier bodies to accommodate the bulk load of food and the size of its digestive systems in the gut areas.
Sauropod Cladogram 

In concentrating on bigger trending torsos, sauropods basically retained ancestral head sizes making it proportionally smaller as compared to the evolving large body. Most sauropod fossil discoveries are minus the head and it’s due to the small skull being easily carried or washed away from the rest of the skeletal remains. But an exceptional sauropod skull discovery of titanosaurian, Sarmientosaurus (Sar-me-in-toe-sawr-us) gives us some glimpses on what this sauropod depended on.

Artist: Marcos Paulo Sarmientosaurus skull/head

The skull measured only 43.2cm/17in, but was attached to a 12.2m/40ft long dinosaur. With all the skull cavities intact, CT scans of the skull showed the brain was the size of a plum, but the scans also detailed sarmientosaurs had highly developed visual and auditory sensory reception; more so than other sauropods. Large eye sockets and long ear canals show that this sauropod had acute vision and was able to hear distant low frequencies. Also, the shape of the skull and neck arrangement shows that the head was held downwards in life suggesting Sarmientosaurus would sweep through low foliage and vegetation.         

To support the heavier body, columnar elephantine same sized quadrupedal limbs evolved, but not like an elephant’s limb distal in splaying outwards creating a wide foot. Sauropod feet had the manus bones arranged in fully vertical columns, with extremely reduced finger bones. Sauropods walked in digitigrade pes fashion where their heel and metatarsals were lifted off of the ground. In eusauropods though, there is exception. Eusauropods were the bigger sauropods with skeletal adaptations to support the weight and lengths utilizing asymmetry in their metatarsal shaft diameters where the thumb metatarsal is broader than the others, shifting the load bearing weight onto the inner half of the feet.

Artists: Raul Martin/Kristina Curry Rogers Rapetosaurus

Sauropod young looked like a miniature adult. This gives credence that the young were on their own in finding food and were not being fed by the parents.
Artist: Dinoraul Mamenchisaurus

It was the sauropod body that affected growth rates resulting in an increased rate of growth. In order to achieve this, some type of metabolic warming had to occur. Sauropods most likely weren’t endothermic, but with their enormous digestive system giving off heat, it’s highly probable they were linked to tachymetabolic endothermy. Tachymetabolism maintains a high ‘resting’ metabolic rate and even though sauropod ‘resting’ metabolism is many times slower than their ‘active’ metabolism the switch was permanently on in generating heat. This is a form of heterothermy as seen in today’s bats and small birds where the animal can switch from poikilothermy to homeothermy and back again.   

Sauropods are known for their long necks. The longest necked sauropods were the mamenchisaurids and a recent 2015 China fossil discovery of Qijianglong (Chee-jee-yahn-long) had one of the longest mamenchisaurid necks. Filled with air sacs, sauropod necks were light weight as compared to neck size. The long necks also contained a long trachea for the lungs to gain more oxygen. From fossil analyses, sauropods neck anatomies experienced, ‘Osteological Neutral Pose’ (ONP) where all the neck vertebrae are neutrally articulated with no deflection up or down. In other words the neck was not disarticulated enough to give efficient sideways motion.

As in today’s giraffes, sexual dimorphism is with the male in having larger necks. Females are more attracted to males with the largest necks. It can be proposed that this scenario as well was with sauropods, as male sauropods indeed did have the bigger necks and it is with this neck dimorphism that over millions of years of time probably led to the most derived sauropods in being the ones with the largest necks.       
Artist: Greg Paul sauropod necks

With long necks and heavy bodies, the tails were also long for counterbalance. The tail also may have been used for defending off predators and using them as a whip snapping the air quick enough to break the sound barrier. This could have been utilized as a warning signal to group members of approaching predators, or to distract carnivores.
Artist: Paleo King With long necks then long tails for counterbalance 

It appears that most sauropods stayed in small bands and clustered with other sauropod species. In the Jurassic, there were nine major subgroups with numerable minor groups composed of numerous genera within each that coexisted. How in the world did they not over compete for food resources and make certain groups lose out to extinction? First off, sauropods, in addition to having spooned or spatula like teeth for grasping and taking in food, other forms evolved another type of dentition of peg-like teeth. This alludes to the fact that varying sauropod families preferred different types of plant foods.
Sauropod dentition

Microscopic studies on the wearing of teeth shows coarsely scratched and pitted wear on the spoon types and finely scratched surfaces on the pegged teeth. In comparing microscopic studies of extant herbivorous mammals and in knowing what they ate, it gives credence to what sauropods long ago ate. Camarasaurids, with the spoon teeth ate coarser plant material, whereas the diplodocids, with the more evolved pegged teeth had the more finely scratched dentition.

This advocates that sauropods ate selectively; one preferring softer foods such as aquatic plants and shoots, while the other consumed tougher shrubs and older plant parts that had collected wind-blown dust grains. It also shows eating behavior patterns as peg-like teeth would work in nipping off shoots or water plants, where spoon-like teeth were far more adequate in grabbing whole mouthfuls of plant material, like leaves and stems. But with apatosaur, nigersaur and rebbachisaur, among others, studies displaying large proportional pitting, fine subparallel scratching dentition and along with blunted square snouts, these sauropod groups likely were nonselective low to the ground grazers. So, sauropods covered browsing behaviors from ground height to mid-level and to upper canopies.

Artist: Steveoc 86 Melanorosaurus

Melanorosaurus (Meh-lan-or-o-sawr-us) lived during the Late Triassic 227-221 mya. Some articles will list Melanorosaurus as a true sauropod, but it is not. It was a most derived sauropodomorph that was however, an intermediate between advanced sauropodomorphs basal to primitive sauropods. It most certainly had sauropod features such as the transitioning to a large sauropod neck bauplan. This of course accelerated an access to a food source that was out of reach for most other herbivores of the day. The extensive pneumatization of the sauropod axial skeleton was also evident in Melanorosaurus as inherited by sauropods. This paved the way for sauropod evolutionary advantages in lowering the energy cost for pulmonary breathing, reducing specific gravity of its mass and would aid in eliminating excess body heat.

Although the forelimbs were slightly shorter than the hind limbs the femur was straight, thick and columnar sitting immediately below the body, although the pes and manus distal metacarpals were disarticulated splaying from one another as in their more primitive predecessors. With true sauropods, the toes and fingers were encased in flesh and not visible; only the claws were. This made for a stronger padded round base in supporting weight.

A common feature Melanorosaurus had with other more primitive sauropodomorphs was in having nine premaxillary teeth, but had up to nineteen maxillary teeth that were common in a lot of the more derived sauropods. This animal was ~10.7m/35ft and although this is small as far as more derived sauropods became to be gigantic, it most likely was the largest animal during its day.

Antetonitrus (An-tee-toh-nigh-trus) lived during the Late Triassic 210 mya. It is a basal sauropod and although it easily walked as a quadruped, the forelimbs were shorter and not as adapted for bearing weight. Antetonnitrus etymology is Latin in ‘ante’ (before) and ‘tonitrus’ (thunder) and is in reference to Brontosaurus (Bron-toe-sawr-us) which is Greek meaning, ‘thunder lizard’.

Artist: Karkemish 00 Antetonitrus

Digit I (first digit or thumb) of the forelimbs was set higher up from the other digits and was twisted 40° making it opposable to the rest of the foot. The manus as a whole wasn’t locked into position inferring digit I was used for grasping. In judging the forefeet, Antetonnitrus was the most basal sauropod in the transitional phase from bipedal sauropodomorphs to true quadrupedal sauropods. Quadrupedalism requires a pronated manus so that it may swing in a parasagittal plane. The distinctive tri-radiate proximal ulna of Antetonitrus and derived sauropods may be linked to a medial shift in the position of the radius that brought about this pronation. Other than the forefeet anatomy, this sauropod had already evolved typical sauropod features of the digestive tract, long necks/tails and columnar bearing limbs directly below the body.

Artist: Fabio Pastori Bilkanasaurus

Blikanasaurus (Bly-khan-ah-sawr-us) was another one that teetered between being designated as a sauropodomorph doomed to a dead end, or to be classified as one of the oldest sauropods thus found. But after recent studies, the conceding final analysis is that it is the most basal sauropod thus discovered, although not as a direct ancestor to behemoth sauropods that were later to come.

Occurring 225 mya in the Late Triassic, as Antetonnitrus, Blikanasaurus had the opposable digit I, but in analysis of its skeletal structure, was one of the first sauropods to have a permanent quadrupedal gait even though digit I was not weight bearing.       

Occurring 110 mya toward the end of the Early Cretaceous was, Brontomerus (Brawn-toe-meh-rus). The name is Greek meaning, ‘thunder thighs’ and for very good reasoning. This sauropod had the largest and strongest thigh muscles of any animal thus far known. The huge muscle projected forward. Even the ilium on which the thigh muscle was attached projected forwards suggesting the ability to deliver a strong forward kick. The ilium further had attachments for abductor muscles allowing the leg to draw up and away from the body. For this roughly, 60 metric tonnes/66 US tons (132,277 lbs.) sauropod with a length of 14m/46ft, the strong hind limbs assuredly gave it advantages not afforded to other sauropods.
Artist: Francisco Gasco Brontomerus kicking Utahraptor

The capable strength and power delivered in this kick definitely could have served a fatal blow to any predator of its day. It may have also served in males kicking it out during mating periods or standing side-by-side kicking one another for leadership dominance. The hind limb musculature also would give Brontomerus an advantage of greater support in going up or down steep inclines and a steadier base for rearing up on the hind limbs. In being able to climb and descend steep hills and to rear safely on its hind limbs gave a greater access to plants that would be unattainable for other large sauropods.
Artist: Tumas Koivurinne Shunosaurus

Living in the Middle Jurassic 170 mya, Shunosaurus (Shu-no-sawr-us), with 21 China fossil finds, was one of the most unusual sauropods. At 9.5m/31ft, it was fairly small for evolving sauropods and had the second shortest neck among sauropods, just behind the shortest neck of Brachytrachelopan (Brak-e-trak-el-o-pan). Brachytrachelopan’s neck is 40% shorter than other sauropods, where Shunosaurus is 37% shorter. This suggests they were low browsers.

Shunosaurus tail fossil

Another Shunosaurus oddity is its upper and lower jaws curved upwards that functioned much like a pair of garden shears in stripping foliage. But the oddest trait was its mimic of ankylosaurs in having the tail end in a bony club topped by two 5cm/2in osteoderm cone-shaped spikes used for fending off predators and perhaps male competitors when mating.           

Rapetosaurus (Phonetics: Rah-pay-to-sawr-us) is thus far one of the last sauropods that held out to the end of the Cretaceous 77-66 mya. It is under the clade, Titanosauria, but as under that order, was very moderate in size at 15m/49ft in length; being half the size of other titanosaurs. Juvenile remains have also been found with its length at 8m/26ft. As pointed out and pictured earlier in a few paragraphs above, paleontologists also discovered an infant Rapetosaurus with its size no more than a medium sized dog. Implementing bone histology and X-ray computerized tomography, the researchers found that the infant had the same ratio of bone compactness per size as the adult alluding to the fact that Rapetosaurus resembled the adult stage throughout all the sub adult stages, indicating a very early independence from parental care. The small size could be referred to island dwarfism as Rapetosaurus was isolated on the forming island of Madagascar that rifted from Africa in the Early Cretaceous 135 mya and India during the Late Cretaceous 88 mya.

Artist: Tyler Keillor Rapetosaurus weeks old 

Rapetosaurus also shared similar skull features of Diplodocus (Phonetics: Dih-plaw-duh-cuss) in possessing a more slender cranium with the nares (nasals) opening up between the eyes. It also had closely quartered pencil-like dentition more suited for stripping leaves away from tree branches.

As a born and raised West Texan, I have to speak of Glen Rose, Texas. The Paluxy River runs through the quaint town and outside a few miles away, dinosaur tracks were discovered in the riverbed. Way back as a child in the late 1950s and early 1960s my siblings and I would scamper down into the riverbed during the dry season checking out the dinosaur trackways and reliving what it would be like to actually see one of those dinosaurs that left those massive limestone foot impressions. It let our imaginations run wild. Today though, that part of the river is Texas’ ‘Dinosaur Valley State Park’.  
Old Paluxy Poster

Theropod track in Paluxy River bed
Dino tracks Paluxy River
Also in those bygone days, in town was a little museum ran by sweet l’il elderly ladies; they all were volunteers from the local 1st Baptist Church. An old farmer said he had found a human footprint alongside the dinosaur tracks. Yeah, he said he dug it up and brought it to the museum. As the l’il ladies explained the farmer story to ya, they also would interject, “It is living proof of the Bible’s creation story.” Once I got a little older, I began to silently question the story for ya see; the supposed human footprint was clearly cement mortar. Now I wondered, how in the world could a mixed cement block come from limestone strata? I did ask the l’il ladies about where exactly did the farmer extract this imprint, but they relayed he never would say in wanting to keep folk away from the premises and all, ya know. Now the elderly gals would eagerly peddle a photo of the footprint made into a poster. I did so kindly as to purchase one and still have it today hanging in my stair well. Blessed are the l’il elderly ladies...

Artist: Cheung-tat Chung Acrocanthosaurus pursuing Paluxysaurus

Anyway, in honoring those childhood days, I give you the Paluxy River’s, Paluxysaurus (Pa-lux-ee-sawr-us). Up to 18m/59ft long there is a portion of a  Paluxysaurus foot path that was excavated along the Paluxy River’s bedrock now housed in New York’s, ‘American Natural history Museum’. The Paluxysaurus tracks are trailed by a large theropod predator, which was most likely left by Acrocanthosaurus (Ak-row-kahn-tho-sawr-us), the most prevalent carnivore of that Early Cretaceous time period. Paluxysaurus lived 115-110 mya and Acrocanthosaurus, 116-110 mya. Although according to its skeletal remains, Acrocanthosaurus wasn’t very speedy. The foot trails depict Paluxysaurus being tailed by a theropod of Acrocanthosaurus’ 11.5m/38ft size range. Paluxysaurus remains were found in Hood County in which Glen Rose is the county seat, while Acrocanthosaurus fossil remains have been found throughout Texas near Hood County. The fossil footprints and impressions may not have been left by Acrocanthosaurus, but the evidence retained in them certainly holds a vast amount of info of that animal.

Artist: Linda Bucklin  B. excelsus 
On a closing note, as but a small child I always equated long necked dinosaurs as a brontosaur. Then as an adult, it was deciphered that the brontosaur fossils were actually just another apatosaur. I so grieved, for I missed my brontosaur. But alas, as an older man there is to be no more grieving as it has been positively borne out through meticulous research that not only is there a brontosaur, but there are actually three species in, B. excelsus (the very one that was removed and reassigned as an apatosaur species then back to brontosaur),  B. yahnahpin, and B. parvus.

Below are a few sauropods:

Artist: James Kuether Apatosaurus
Artist: Luis V. Rey Amargasaurus
Artist: Luis V. Rey Astrodon fending off pesky Utahraptors
Artist: Phil Wilson Brachiosaurus
Artist: James Kuether Omeisaurus

Artist: Kostyantyn Ivanyshen Titanosaurus

Besides the common bird-hip, ornithoscelidans were also intermediate in bird structure with various ornithischian species possessing integumentary filaments, quill-like appendages and feather-like epidermal branching structures. Of course in theropods, distinct evidence in ulnar quill knobs, down feathering and feathers have been found in their fossil remains. In both of these dinosaur groups there is also fossil evidence of epidermal scales, just as it is present in bird legs today. So for dinosaurs comprising, Ornithoscelida, scales and feathering were evident in skin covering as a whole, or in part or in possessing both.  

Ornithoscelida simple clades

This new dinosaur cladistic relationship grouping also suggests that hyper-carnivory was acquired independently in herrerasaurids and theropods, offering an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians. The earliest theropods, ornithischians and also sauropodomorphs to arise, basically came from the same grandparents; it’s just that theropods and ornithischians were first cousins and second cousins to sauropods in matter of terms.  

First off, please don’t confuse ‘Ornithoscelida’ with ‘Ornithischia’, for it’s easy to do. They are as distinct from one another as Australopithecus is to Homo sapiens. One covers multiple variant groups (Ornithoscelida) while the other (Ornithischia) carries a few specific related subgroups.

Ornithischia Cladogram

Ornithischians came in many various forms as quadrupeds and bipeds, as armored or bony, but what primarily designates a dinosaur to be related to the ornithischian club is the pelvic anatomy. Ornithischian pelvises, or hip girdles have the pubis and ischium bones running parallel to one another pointing backwards just below the ilium which points forwards. This is extinct and extant bird hips’ typical arrangement, thus the name, Ornithischia which is Greek for ‘bird hipped’. They also possessed ossification on the predentary of the dentary (lower jaw) that formed a beak extending the dentary in coinciding with the upper premaxillary.

Other ornithischian characteristics were toothless paired premaxillary bones with a keratinous tipped beak and possessed a palpebral bone that laid across the outside of the eye socket (similar to an eyebrow function in humans). Also, these dinosaurs shared a much reduced or closed off antorbital fenestra (skull openings in front of the eyes) and stiffened backbones near the pelvis due to ossified tendons above the sacrum. All ornithischians were herbivores.

Those with teeth bore leaf-shaped, or premaxillary spoon-shaped dentition or a battery of peg-like teeth set in back of the mouth that was surrounded by rhamphoteca (keratinous sheaths). Ornithischians with dentition chewed softer plant material inaugurating the digestion process. The keratinous beaked ornithischians with few or no teeth relied on a large gut for bacterial fermentation.

Some, like the ceratopsid, Psittacosaurus (Phonetics: Sit-tah-coe-sawr-us), the ankylosaurid, Panoplosaurus (Pan-op-low-sawr-us), the iguanodontid, Iguanodon (E-gwan-o-don) and the hadrosaurid, Claosaurus (Clay-o-sawr-us) had gastroliths found in the gut area of their fossil remains, but other than these four dinosaurs, gastroliths are not evident in ornithischian fossils. To induce proper digestion in assimilating nutrients from plant bulk, most ornithischians may have incorporated gastric milling. This is a process where a musculature stomach is equipped with a layer of hard keratin and small pebbles which breakup, pulverize and emulsify food content. Toothless ostriches today incorporate the same process. As ornithischians are related to theropods and birds evolved from theropods, it is conceivable herbivorous birds genetically inherited gastric milling from ornithischians. Found at the front of the lower jaws, all ornithischians possess a predentary bone that functions as an aid in cropping plants.

Ornithischians are divided into two major subgroups; they are: Thyreophora (Thyr-uh-ree-off-for-uh) and Cerapoda (Sair-uh-po-duh). The clade Cerapoda further divides more derived ornithischians into two subgroups, Ornithopoda (Or-nith-op-o-duh) and Marginocephalia (Mar-gin-o-seff-fol-e-uh). Cerapods were the bird foot dinosaurs where marginocephalians were the ‘bone headed’ and ‘horned face’ dinosaurs. The dinosaurs that make up these three clade groups are:

Thyreophora: ankylosaurs, stegosaurs.

Ornithopoda: hadrosaurs, hypsilophodontids, iguanodontids, thescelosaurids, jeholosaurids, yandusaur.

Marginocephalia: A) Pachycephalosauria ~ pachycephalosaurs; B) Ceratopsia ~ Yinlong, Chaoyangsaurus, psittacosaurids, ceratopsids.

Although the Late Triassic suchian, Revueltosaurus (Re-vul-toe-sawr-us) living 225-209.5 mya was originally thought to be a basal ornithischian, it appears that ornithischians did not arise until the Jurassic, as revueltosaurs were finally determined to be a clade of suchian archosaurs.

Revueltosaurus skeletal anatomy

Fabrosaurs, agilisaurs, nanosaurs and gongbusaurs occurring throughout the Jurassic 199-155 mya ago, have scant fossil finds and cannot be reliably classified, but at what has been found and studied, they are primitive bipedal ornithischians. Ranging from 1-2m/3.3-6.6ft in size, unless perfectly fossilized, their fragile remains were easily disintegrated throughout the eons of Earth upheavals and weathering.
Artist: Wayne Barlowe Fabrosaurus

After much debate, Pisanosaurus (Pi-san-o-sawr-us) has been determined to be the oldest ornithischian thus far discovered despite the fact it is not a true dinosaur, but a dinosauriform. Although it is not a true cerapod, it does show ornithopod anatomical features with affinities to hypsilophodontids and heterodontosaurs and is the earliest known bird-hipped animal. Living 228-216.5 mya in the Late Triassic, Pisanosaurus was a biped herbivore reaching a length of 1m/3.3ft. The acetabulum (hip-joint) is open, low and axially long, due to the short pedicels of the ilium. The upper region of the ischium is wide and larger than the pubic bone. Pisanosaurus is the sister group of the basal ancestor to heterodontosaurids and thyreophorans.

Artist: Masato Hattori Pisanosaurus

Occurring in the Early Jurassic 199-189 mya, Lesothosaurus (Leh-so-toe-sawr-us) was only 1m/3.3ft long, but with good fossilization more is known of this ornithischian. Lesothosaurs are one of the first true dinosaurs to have evolved the bird-hip. The hind limbs were long in proportion to body size while the forelimbs were short, but with four well developed metacarpals (finger bones). The anterior end of both the lower and upper jaws was a characteristic ornithopod-like keratinous beak for snipping off plant material. Inside the mouth in the front were canine-like teeth followed by leaf-shaped teeth in the lower jaws that meshed with the horny beak in an up and down motion to shear food. There is evidence that lesothosaurs traveled in small herds.

Artist: Albert Gruvitz Lesothosaurus

Heterodontosauridae (Hay-tear-o-don-toe-soar-uh-day) species are the most basal members of ornithischians. Occurring from the end of the Triassic through the Jurassic and on into the Early Cretaceous 201-133 mya, the heterodontosaurid family consisted of three genera and one subfamily, Heterodontosaurinae composed of five genera as illustrated in the cladogram below.
Heterodontosaurid Cladogram

Credit: NRF S. Africa Abrictosaurus
Heterodontosaurid dental evolution
Heterodontosaurids were similar anatomically and small with no species ever exceeding 2m/6.6ft. As in the lesothosaurs, they maintained inheritance from their predatory ancestry in possessing caninform dentition and depending on species, were located either on the premaxillary in earlier forms or the maxilla in more derived forms. The canine-like teeth were serrated either on both the anterior and anterior sides or only on the anterior side of Abrictosaurus (Ab-rick-toe-sawr-us). However, in their dentition evolvement, the ancestral canines were transitioning to a more herbivorous tooth form. The cheek teeth had small denticles (ridges) to crop and masticate vegetation. The mandible was tipped by a unique ornithischian bone called predentary that was situated on the front upper jaw extending the dentary (lower jaw bone). The predentary supported a toothless keratinous beak as did the upper premaxilla. 

A) Heterodontosaurus B) Tianyulong
This differing dentition arrangement is what gave rise to the family name, as heterodont dentition is an animal possessing more than a single-type of tooth morphology; just as primates do, which includes humans. As far as the skull goes both Abrictosaurus and Heterodontosaurus, the jugal bone projected sideways as it did in the later more derived ceratopsians. As shown in the illustration below, one of the main features that distinguished heterodontosaurid species from the others was in the jaw articulation angle of the skull.
Heterodontosaurid fossil with feathering integuments

One of the striking features found in heterodontosaurid fossils are the impressions formed from filamentous integumentary structures on the back, tail and neck, which are a theropod variant of protofeathers. Also, heterodontosaurid forelimbs were lengthening; a trending factor towards quadrupedalism.

Artist: Julio Lacerda  Heterodontosaurid perching

One unique anatomical characteristic found in at least some, like the pigeon-sized Manidens is in the feet. The pes (foot) had a raised ridge on the back near the ankle and is interpreted as an area for additional tendon attachment. The toes were unusually long ending in narrow and curved claws resembling many birds. Finally, the first toe had a unique combination of characters suggesting that it may have been able to grasp objects despite being shorter than the other three toes. This comes to the conclusion that like most perching birds; some heterodontosaurids could clamber and perch upon tree limbs.
Artist: Masato Hattori 

One Late Jurassic 150 mya heterodontosaurid was Fruitadens (Phonetics: Fru-tye-dens). Measuring only 65-75cm/25-30in in adult length, it was a small ornithischian. This diminutive dinosaur was also the only ornithischian omnivore as evidenced by its dentition and no, it did not eat fruit. The name comes from the locale its fossils were found in, which is near the town of Fruita, Colorado. Remember, fruiting plants didn’t come about until a good 20 million years later in the Cretaceous. With hind limbs as long as its head and torso, it was a swift runner.

Artist: Tyler Keillor Pegomastax

One other heterodontosaurid was even smaller at 60cm/2ft. Occurring 200-190mya in the Early Jurassic, Pegomastax (Peg-o-mass-taks) was an herbivore that utilized its dentary fangs to uproot plants, dig for roots and as a secondary use in defense. In possessing the paired fangs, porcupine-like dorsal quills and extremely long legs for sprinting, this dinosaur was defensively equipped no matter its size.

A few more heterodontosaurids:
Artist: Nobu Tamura Tianyulong
Artist: Luis V. Rey Heterodontosaurus tucki
Artist: Nobu Tamura Manidens

Thyreophora: Thyreophorans comprise the ankylosaurs and stegosaurs; the armored dinosaurs. Their temporal range was from the Late Jurassic to the Late Cretaceous 199.6-66 mya. Utilizing etymology, Thyreophora is derived from the Greek ‘thyreos’ (shield) and ‘phoros’ (bearer), in reference to their various types of armor. Instead of feathering, thyreophorans opted for heavy ossification and osteoderm skin covering. Except for the basal thyreophoran, Scutellosaurus (Skuh-tell-o-sawr-us), all other thyreophorans were quadrupeds walking on all fours with shorter forelimbs than the hind limbs.

Basal or primitive thyreophorans had not yet developed the armored osteoderm plates that the more derived forms, like stegosaurs and ankylosaurs are known for, but from fossil studies of preserved soft tissue, it is concluded that most basal thyreophorans possessed an outside layer of keratinous skin. From this, the armor derived in the later forms.

The most primitive thyreophoran evidence thus found are, Tatisaurus (Tah-tee-sawr-us) found in China’s Lufeng Formation of Early Jurassic sedimentary rock dated 199.5 mya and Bienosaurus (By-no-sawr-us). Bienosaurus was also found in the same ‘Lufeng Formation’ as Tatisaurus and is estimated to be from 195+ mya. Both of these finds are skimpy and Tatisaurus is considered to be nomen dubien due to the fossil only being a dentary (lower jaw) with teeth still intact. But the teeth and jaw have enough traits to tie it into its ornithiscian fabrosaur ancestry and thyreophoran lineage. Bienosaurus’s fragmentary skull and jaw remains have close affinities to the thyreophoran, Scelidosaurus (Scale-e-do-sawr-us).

Artist: Luis V. Rey Scelidosaurus

Occurring 196 mya in the Early Jurassic, Scutellosaurus is one of two of the most basal thyreophorans that led to the more derived armored forms. Scelidosaurus, from 191 to 183 mya of the Early Triassic, is the other. Both were strict herbivores. With only a maximum length of 1.2m/3.9ft, Scutellosaurus was bipedal, but with longer hind limbs, the shorter forelimbs were still long and built strong enough to perform weight bearing qualities, so it could walk in a quadrupedal stance with ease. It possessed osteoderms that were fixed as plates of bone within the skin. The osteoderms ran dorsally down the back and flanks in parallel rows. This would have given Scutellosaurus an advantage from early theropods of the day in protecting it from teeth piercings of the skin and internal organs. Of course more derived theropods evolved into larger forms and stronger bites, so thyreophorans in kind evolved into larger sizes with more armor. Scutellosaurus had a long tail that was likely used as a counter balance to the heavier armored body.

Artist: James Kuether Scutellosaurus

Closely related to Scutellosaurus, Scelidosaurus was a notch above in the armory. Still retaining the shorter forelimbs, Scelidosaurus was fully quadrupedal and possessed six rows of osteoderm bony plates down the dorsal and flank sides of the body, with the back four dorsal rows ending at the tail tip. In addition, there were three pointed plates just behind the skull. A well preserved Scelidosaurus fossil find showed preserved soft tissue around the vertebrae that was an epidermal layer of keratinous skin overlaying the osteoderms. At 4m/13ft long, Scelidosaurus was nearly triple the size of Scutellosaurus and is the sister taxon to the two main thyreophoran clads of stegosaurs and ankylosaurs
Credit: BBC Co. UK Scelidosaurus fossil
Representing an immediate form between Scutellosaurus and Scelidosaurus, the 4m/13ft long Emausaurus (Em-ow-sore-us) from the Early Jurassic 184-176 mya, had a skull anatomy that was very similar to Huayangosaurus, (Hue-way-ang-o-sawr-us). The Emausaurus skull was also small compared to its 4.5m/14.8ft body that was also to become a distinguishing feature of stegosaurs.

Artist: Graham Rosewarne Emausaurus

The two major thyreophoran clads are the stegosaurs and ankylosaurs. The clad, Stegosauria covers fourteen species and Ankylosauria covers six species. Stegosaurians are known for their rows of bony upright spikes or plates running down their spines while the more armored ankylosaurians are more known for patches of external bones fused into protective plates. Stegosaurs’ temporal range was from the Middle Jurassic to the Early Cretaceous 165-136 mya. Ankylosaurians had a longer temporal range from the Middle Jurassic to the Late Cretaceous 167-66 mya. Ankylosaurs were one of the last groups of dinosaurs to go extinct.
Artist: Franco Tempesta Huayangosaurus
Hesperosaurus varying gender plates
Stegosauria ~ As descendants from the Lesothosaurus lineage, stegosaurians evolved their armor from a dinosaur line that had none. But, lesothosaur traits were maintained as the earlier stegosaurian forms were smaller and could run. Stegosauria includes the two families, Huayangosauridae and Stegosauridae. The more derived forms, as in the family Stegosauridae evolved longer hind limbs hampering running abilities, but gave a greater advantage in using the spiked tail for defense in trajectory, torque and height. Stegosaurians walked with an erect Limb gait, holding the body and tail upright. The dorsal bony plates running down the spine that make for stegosaurian fan clubs were not for thermoregulation, but for protective defense and were possibly an example of sexual dimorphism being colorized in males for attracting mates. Female plates were more grays or browns. Also, in taking advantage of a single species, (Hesperosaurus mjosi), central Montana graveyard site, by applying geometric morphologies it’s been found that adult male plates were much broader and rounder than the females, narrower plates. This gave more visibility for attraction. Later forms possessed a vertical bony plate covering the outer side of the lower jaw and a low ridge structure in the upper jaw running parallel to the tooth row. This is indication of a fleshy cheek pouch existing.
Artist: Masato Hattori Hesperosaurus mjosi male
Huayangosaurus was a basal stegosaurian found in China and as such, Asia is the origin of stegosaurians. Coming from the Middle Jurassic 165-163.5 mya, Huayangosaurus is a basal stegosaurian and was small at 4.5m/15ft in length when compared to the more derived forms. It also possessed from its ancestral line premaxillary teeth that were disposed of in later forms. Called ‘thagomizers’, it was the first stegosaur to possess these spikes (thagomizers) on the end of its tail which were two paired extending outwards horizontally and sideways. In addition to having the rowed paired of bony plates running down its back, above its hips in the plate rows were paired spikes. As for the plates themselves, they were narrow and tipped as opposed to later stegosaurian plates being more rounded. With a low stance and broad skull, Huayangosaurus was a low browser and did not have adaptive capabilities for a specialized diet.

A) Correct B) Wrong Gigantspinosaurus
There is ongoing disagreement if Huayangosaurus supported side shoulder spikes. Some paleontologists say yes, as extra spikes were found in fossil remains. Others conjecture that these extra spikes were washed from other stegosaur fossil sites. This is why on a lot of Huayangosaurus illustrations you will find added shoulder spikes and on some ya won’t. Regardless, on the most primitive stegosaurian in, Gigantspinosaurus (Gye-gants-pine-o-sawr-us), it did possess large shoulder spikes as an extension of the shoulder blade (scapulae) assemblage that pointed upwards then curved dorsally toward the posterior end. The spikes are now known as ‘parascapular spines’. Due to their positioning, these spikes weren’t used as weapons, but as a predator deterrent much like the plates were used as protective armor. Gigantspinosaurus occurred in the Late Jurassic mya, but the name does not refer to its size as it was only 4.2m/14ft long. The name refers to the flank spikes meaning, ‘giant spined lizard’.

Artist: James Kuether Gigantspinosaurus

Occurring around 160 mya, its plate rows were also narrow and tip pointed just as Huayangosaurus, but ended just before the tail. Huayangosaurus and Gigantspinosaurus had a unique feature that was absent in all other subsequent stegosaurians in having ossified tendons extending down the vertebral column.

Stegosauridae is the family of stegosaurs within the suborder of Stegosauria. It’s defined by all the stegosaurians having a closer relationship to Stegosaurus (Steg-o-sawr-us). Stegosaurids roamed in the Middle Jurassic to Early Cretaceous 165-136 mya. The vast majority of stegosaurians so far recovered belong to Stegosauridae with most species arising from the Late Jurassic and Early Creataceous, but by the latter part of the Early Cretaceous there was a decline in diversity and speciation. There was a fossil find in India coming from the Coniacian Stage (89.8-86.3 mya) of the Late Cretaceous that was once thought to be a stegosaur dubiously named, Dravidosaurus, but turned out to be a plesiosaur. The decline and final extinction might be due to a floral turnover when angiosperms began to dominate, drastically reducing cycadophytes which corresponded with the stegosaurid decline. As it stands, Wuerhosaurus (Where-ho-sawr-us) at 5m/16ft long living ~ 136 mya in the Early Cretaceous, was the last of the stegosaurs to go extinct. Stegosaurids were evolving wider hip placements and Wuerhosaurus, as one of the last stegosaurids had the widest hips. This is thought to be the result of enlargement of the digestive tract. Stegosaurids also possessed flexible armor-like scales that protected the throat.

Artist: Masato Hattori Wuerhosaurus
Artist: Vladimir Nikolov Kentrosaurus
Kentrosaurus (Ken-tro-sawr-us) that had a temporal range of 155.7-150.8 mya in the Late Jurassic was the most basal stegosaurid. A close descendent to the Gigantspinosaurus lineage, it too had flank spikes but were much smaller. Anatomically however, its osteological frame was closer to stegosaurids, such as the dorsal vertebrae having a neural arch more than twice as high as the centrum, completely occupied by an extremely spacious neural canal. Also, it possessed a stegosaurid ilium feature of the pre-acetabular (anatomy situated in anteriorly of acetabular) process widening laterally instead of tapering as the more basal stegosaurian fossils exhibited.
Artist: Mohamad Haghani Miragaia

Miragaia (Meer-uh-guy-uh) as a stegosaurid, also retained the shoulder spikes that were long and pointed at the tips; although there is current debate if the spikes were from the shoulders or actually were a specialized tail spike. In addition, this odd stegosaurid with a temporal range of 150 mya in the Late Jurassic had unique rows of eight paired plates that were tipped like a picket wooden fence transitioning down into the body’s dorsal side asymmetrically with a convex outer side and a concave inner side. The plates’ base weren’t as expanded as other stegosaurids except for the last narrower pair. The plates ran down the spinal column from the back of the head to the rump. Beyond the rump and down the tail, the plates were transformed into spikes.

The most unique attribute of Miragaia however was its neck. Through a Hox gene switch trigger, it’s theorized these regulatory genes that organize organism body plans, once activated from dormancy, induced back vertebrae to be carried forward becoming neck vertebrae. As a result, Miragaia had 17 neck vertebrae giving it the longest neck of all other stegosaurians, even more than most sauropods, by almost doubling the neck vertebrae count in the other stegosaurid members, even though more derived stegosaurs were evolving lengthened necks. It may never be truly clear what natural selective pressures were lengthening stegosaurid necks and in particular Miragaia’s neck. It could be an advantage to reach higher for food sources in utilizing the tail and hind limbs in a tripod stance since its body’s center of gravity was more towards the hips. Or, it was to use the neck in a swaying back and forth motion to vacuum up lower plant material in swoops. Or it could even have been a sexual attractant to the opposite gender. With the lengthened neck, Miragaia’s total length was 6m/29ft.

One other thing on Miragaia, its remains were found in Portugal where most stegosaurid fossils have been found in North America. This only verifies continental drift as Miragaia’s temporal range was when N. America was connected to Western Europe.               
Artist: Karen Carr Stegosaurus
Stegosaurus (Steg-o-sawr-us) in modern culture is the famous dinosaur that the family, Stegosauridae is named after. Living in the Late Jurassic 155-150 mya, this stegosaur was a low browser feeding on soft vegetation. Its bite force was less than a human’s due to weak jaw muscles, so it nipped off soft vegetation with its turtle-like beak by pulling the head back. It then relied on its 78 small triangularly flat teeth to chew the food thoroughly before swallowing, allowing the enlarged gut aided with gastroliths to do the main digestion of nutrients. It did indeed eat well though for its total adult length was 9m/29.5ft in length, making it the largest of all stegosaurids.

Stegosaurus had a graviportal gait in that it was adapted to moving slowly. This was not due to dimwittedness. An excellent fossil find of a well preserved stegosaurus braincase showed that the brain cavity held a brain weighing no more than 80g/2.8oz. This is about the size of two walnuts. Very small, for a 4.5 metric ton/5 short ton animal, but the graviportal gait was solely due to a high body weight as a result of the long hind limbs and not due to brain size. There were three species of stegosaurs in S. stenops, S. ungulatus and S. sulcatus.

Stegosaurs had two pairs of spikes at the end of its tail that pointed outwards for defense. The main stegosaur predators were allosaurs. Paleontologists have found allosaur fossils with puncture wounds that stegosaur thagomizers (tail spikes) would perfectly fit into.

A few more stegosaurs below:         
Artist: Alain Bénéteau Lexovisaurus defending against Allosaurus
Artist: Cisiopurple  Stegosaurs
Artist: James Kuether (Paleoguy) Tuojiangosaurus defending against Yangchuanosaurus

Ankylosauria ~ The sister group to stegosaurians, were ankylosaurians, the tank of dinosaurs. I personally prefer referencing ankylosaurians as the dinosaur equivalent to armadillos. Standing low to the ground, they were not fast runners with short stocky limbs and as armadillos, their ventral side or underbelly was void of any armored protection as the rest of the body was; just like armadillos. Armadillos protect the vulnerable underbelly by curling over it, while ankylosaurians mastered the low to ground stance under a heavy and broad armored body to protect it; differing methods fashioned toward the same end result.
Ankylosauria clade

Ankylosaurians were low browser feeders and due to whatever foliage was available in ecosystems of their biomes, evolved differing methods for assimilating food. As borne out through tooth wear and mandible articulation studies, some groups chewed with tooth occlusion (teeth contact) accompanied with palinal (backward motion) jaw movement. Other groups chose a widening and shortening of the muzzle evolving a convergent precise tooth occlusion, while others evolved the same process aided by an additional palinal power stroke with a narrowing and elongation of the muzzle. In the more basal groups of Asia, processing food was restricted to orthal (vertical motion effects) pulping. These types of nutrient assimilation were evolutionary responses to what flora was presented, as with only an inflexible neck reach of no more than one meter ankylosaurians had to depend on whatever foliage was available near the ground. However, the hind limbs were capable enough in holding the body weight if the dinosaur wanted to support itself on a trunk with the forelimbs to get at low hanging branches.

The enameled phylliform (leaf shaped) teeth as triangular shaped, were similar to stegosaurians and were replaced when worn out. Possessing hyoid bones, suggests they had long flexible tongues to wrap around soft food plants and had a large secondary palate indicating they were able to still breathe while chewing.          

Distinguished features of the heavily ossified ankylosaurian skull shows that this group evolved early by splitting off into its two main families of, Nodosauridae (No-doe-sawr-uh-day) and Ankylosauridae (An-kill-o-sawr-uh-day). The ankylosaurian tail evolved one step at a time from the stiffened nodosaurid tail to the ankylosaurid tail ending in bony clubs.     

Nodosauridae: Nodosaurids were the first of the ankylosaurians to appear 155 mya in the Late Jurassic, becoming extinct 66 mya at the end of the Cretaceous. Nodosaurids are considered to be more related to Panopolosaurus (Pan-op-lo-sawr-us) than to the ankylosaurids. All nodosaurids had neck and flanked body spikes projecting outwards sheathed over with keratin, except for Panopolosaurus where spikes were absent. All nodosaurids had heavy osteoderms and bony nodule rows running dorsally down the back and sides of the head and body. Unlike as their ankylosaurid kin, the tail ended in a typical dinosaur tapered, but flexible tip with no armaments. The snouts were relatively narrow and triangular shaped indicating a preference to selective browsing of low growth plants.

Nodosaurids had a global distribution, including Antarctica in the genus, Antarctopelta first mentioned above under Dinosauria. They all became extinct by the end of the Cretaceous, but it was not an abrupt event due to the asteroid impact; it was more of a gradual decline in family members.  
Mymoorapelta skeletal anatomy

Living 155-150 mya in the Late Jurassic, Mymoorapelta (My-moor-ah-pel-tah) is the most basal nodosaurid currently discovered and was found in Colorado, USA. The oldest known nodosaurid from Europe is from the Early Cretaceous 112 mya named Europelta (Your-o-pel-tah). It had some odd traits in having the ratio tibia to femur lengths greater than any other ankylosaurian, possessed autapomorphic (a derived trait unique to one species) osteoderms located on the outer corners of the pelvic shield and the skull was covered by a single osteoderm. With fossil remains found in Austria, the last nodosaurid to go extinct was, Struthiosaurus (Stru-the-o-sawr-us) living in the Late Cretaceous 85-66 mya. At 2.2m/7.2ft long, it was also the smallest of the ankylosaurians.
Artist: Roman Garcia Europelta

Nodosaurids fossil remains have been discovered in near shore marine sediment topologies suggesting that they preferred littoral coastal plain habitat, with some carcasses washed out to sea. Ankylosaurid fossil remains have only been found inland in more upland habitats.

Artist: David Bonadonna Borealopelta drowning

As described more like a mummified dinosaur or a statue of one, the fossil remains coming from an open pit oil shale mine in Alberta, Canada is one of the most well preserved fossils ever to have been discovered. In fact, the whole body is in place giving a 3-D image of a sleeping animal. The nodosaurid, Borealopelta (Bor-e-al-o-pel-tuh) occurred ~ 110 mya near the end of the Early Cretaceous. The fossil was found in marine sediment and was washed out to sea in the Cretaceous landlocked shallow ‘Western Interior Seaway’.
Where Borealopelta was found N.G.
Studying the pigments in the fossil’s preserved skin, it’s been determined the body coloration was a reddish brown in a counter-shaded pattern most likely for camouflage. Unfortunately, before the miners spotted the fossil the posterior portion was pulverized into unusable debris by heavy digging equipment.

Borealopelta's fossil
Below a few more nodosaurids:

Artist: W. Parsons Tatankacephalus

Artist: Masato Hattori Hylaeosaurus

 Ankylosauridae: Where ankylosaurids don’t have long spikes on the neck and shoulders, but have a tail ending in a weaponized club, nodosaurids had long spikes on the neck and shoulders but a clubbed tail was absent. Found only in the Northern Hemisphere of N. America, Europe and Asia, ankylosaurids lived in the Early Cretaceous 122 mya until the Late Cretaceous 66 mya.

The ankylosaurid clubbed tail first evolved by weaving caudal vertebrae into bulbous bundles. As the mapped out evolutionary history of ankylosaurid tails portrayed, earlier ankylosaurids bear out the gradual fusing of the tail vertebrae making it less flexible in successive speciation. This essentially turned the tail into a stiffened rod enacting it to work as a handle. If the tail had still been flexible, it would not have supported the weight of the club, potentially tearing tendons and muscle. Also, the stiffened tail, before the club evolved, most likely was already being used for defense by swinging it into the legs or torso of an oncoming predator; much like a nightstick or billy club. The knobbed club was formed by osteoderms fusing in layering bone within the skin at the tip of the tail.        
Ankylosaurid skull

Ankylosaurids had shorter limbs than nodosaurids which would make it harder for a predator to overturn in getting at the non-armored underbelly. With massive skulls, ankylosaurid heads were as broad as long and were shaped as triangular with dermal scutes/plates solidly ossified to cartilage bone. The spine was rigid and curved permanently arching the back.

Credit: Australia Kunbarrasaurus

Considered as basal to ankylosaurids was the ankylosaurian, Kunbarrasaurus (Coon-bah-rah-sawr-us) formerly known as ‘Minmi’, but now has been designated its own genus. It lived 119-113 mya during the Early Cretaceous. The fossil remains were found near the region in Australia’s ‘Minmi Crossing’ in the Allaru and Bungil Formation made up of sandstone, siltstone and mudstone sediment. The cranial endocast (brain casing) is similar to later more derived ankylosaurids, but other head features were very unique. It had more of a tuatara-like proportionally enormous inner ear and a nasal airway that looped back in on itself, where ankylosaurids had straw-like nasal passages. Gut cavity fossil remains consisted mainly of fibrous plant tissue fragments from twigs and stems, with lesser amounts of seeds and fruiting bodies swallowed whole. The chopped fibrous material and lack of gastroliths suggest that food was snipped with the beak and masticated thoroughly before swallowing.

Artist: Eloy Manzanero Chuangqilong

Chuanqilong (Shwahn-chee-long) lived during the Early Cretaceous ~ 110 mya in what is now China and is considered one of the earliest basal ankylosaurids. The most derived ankylosaurid and last to go extinct was Ankylosaurus from 66 mya. It was also the largest ankylosaurid reaching lengths of 8m/26ft.
Credit: Ji Q., Wu X., Cheng Y., Ten F., Wang X, Ji Y. Lianpningosaurus

All ankylosaurians were strict herbivores. Well that is absolutely true except for one major exception; the ankylosaurid, Liaoningosaurus (Lao-nin-go-sawr-us) indeed ate plants, but supplemented its diet with at least fish making it also a piscivore. This Early Cretaceous ankylosaurid, living 122 mya had partially digested several fish remains found within fossilized gut cavity. It was found in China’s Liaoning Province in the ‘Yixian Formation’ that is made up of volcanic basaltic rock and siliciclastic volcanic material. The fossil was of a complete sub adult that either scavenged or hunted fish. There is fossil evidence that it was at least semiaquatic with longer leg ratios to body as compared to other ankylosaurids and there was lack of hip fusion allowing more flexibility in hind limb paddling. Also, the tail was flexible enough for sinusoidal propelling, found in no other ankylosaurian stiffened tail fossils. It also had a flat single osteoderm covering the ventral (belly) portion of the body. This would have protected the underside from predators attacking from below as it swam in freshwaters. However, there is now discussion on whether the belly plate is a true bony osteoderm or preserved skin.

Below are a few more ankylosuars:     
Artist: Sydney Mohr Above: Gobisaurus Below: Ziapelta
Artist: Cisiopurple Ankylosaurids
Artist: Jake Baardse Ankylosaurus

Cerapoda: As mentioned above under Ornithischia, cerapods are divided into two groups: the ornithopods and the marginocephalians. Under marginocephalians, cerapods are further divided into two subgroups in the ornithopodans and ceratopsians. Cerapods arose during the Middle Jurassic 169 mya and went extinct in the Late Cretaceous 66.5 mya.
Simple Cerapoda Cldogram
A bit more detailed Cerapoda cladogram

Cerapods transitioned and radiated out throughout the Jurassic and into the Cretaceous. The main cerapod success was in their dental adaptations evolving ways to thoroughly extract maximum nutritional value through intensive mastication of plants that were otherwise too tough and rough for other dinosaur digestive tracts. Cerapod species were the first to assimilate thorough digesting limited primarily to chewing. It wasn’t until much later that mammalian herbivores would take up this role.

The term, Cerapoda combines its two subgroups with ‘cera’ (horned) from ceratopsians and ‘poda’ (foot) from ornithopodans.

Ornithopoda: There were three distinct family clades of ornithopods belonging to the families, Hypsilophodontidae (Phonetics: Hip-sill-loff-o-dawnt-uh-day), Iguanodontidae (E-gawn-o-dawnt-e-day) and Hadrosauroidea (Had-row-saw-roi-dee-uh) were ornithopods with a temporal range from the Early to Late Cretaceous 130-66 mya. Ornithopods were bipedal but occasionally could maneuver a quadruped gait. These groups were low browsers grazing on plant roughage that was easily cropped and masticated due to the evolving dentary assemblage and chewing mechanisms. It was the most sophisticated form of assimilating food than any other herbivorous non-avian dinosaurs. Later forms of ornithopods developed curved spines allowing them to graze on all fours.         
Artist: Oscar Sanisidro Hypsilophodon

Hypsilophodontidae: This family group is now being considered paraphyletic as the last descendent form from its common ancestor. Where before other genera were included, it now only includes the one genus species, Hypsilophodon foxii (Hip-sill-loff-o-don = fox-eye). Although this small ornithopod (1.8m-5.9ft) occurred well into the Early Cretaceous 130-125 mya), Hypsilophodon had very primitive ornithischian features much like Pisanosaurus and may have been omnivorous. Like the common opossum, Didelphis marsupialis, there were never enough environmental pressures to further stress evolvement.
Artist: Mark Hall Oryctodormeus

Close ornithischian relatives to Hypsilophodon, were two burrowing dinosaurs in, Drinker (Phonetics: Drin-ker) occurring ~ 150 mya in the Late Jurassic and Oryctodromeus (Phonetics: Oh-rik-toe-dro-mee-us) occurring nearly 100 million years later in the Late Cretaceous 95 mya. Named after pioneering paleontologist, Edward Drinker Cope, Drinker was a primitive basal relationship to Hypsilophodon and while Oryctodromeus was related to Hypsilophodon, it was also basal within the line of ornithopods.

These two herbivorous biped swift runners were around 2m/6.6ft long and had modified forelimbs, broad snouts, flexible tails, slender pelvises and shoulder girdles. These adaptations represent a burrowing lifestyle. In fact, there was a family of Oryctodromeus in a fossil find that had a parent and young. The collapsed burrow portion of the fossil discovery had solidified previously dug up loose dirt and was filled with sand that turned into sandstone as a stark contrast from the formation’s ambient mudstone and claystone. The den was much like hyenas excavate today.

Added burrow advantages were safety from predation and extreme temperatures. In addition, in finding the family huddled together, the fossil find points to parental care. With that in mind, both parents in this scenario were taking care of the young. We can only imagine the scene this fossil represents of this cave-in with the frantic behavior of the one parent outside realizing there was nothing it could do to extricate the family from being buried alive.
100 mya honeybees amber fossil
Iguanodontidae: First this about plants before discoursing iguanodontids. Direct ancestors of angiosperms (flowering plants) evolved from gymnosperms (seed producing only plants) in the Triassic 245-202 mya. In turn, these angiosperm ancestors first evolved into true angiosperms 160 mya. As bees evolved from wasps in the Early Cretaceous 130 mya, by 120 mya, angiosperms aided by bees dominated landscapes. In addition to spreading pollen, bees had also hybridized angiosperms diversifying flowering plants. Angiosperms became a nutrient rich food source for ornithopods, further enhancing these dinosaurs’ large population success rates. By co-evolving with the radiation of angiosperms, ornithopods had spread globally.

Iguanodontid manus (hand) fossil
Iguanodontid jaws when closed, exhibited contact between the lanceolate-shaped maxillary teeth and dentary teeth. Premaxillary teeth were absent. As far as the manus and pes assemblage, distal features of the forelimb had digits II, III and IV close together in that for some cases III and IV were bound by skin layers forming a single unit for quadrupedal locomotion. Along with the fused wrist bones, the phalanges fused into a spike on digit I (thumb). Digit V was long, flexible and opposable. For the manus the hind limbs ended with digits II, III and IV being short and wide with blunted claws that were hoof-like.

Monophyletic Iguanodontid Clade

Iguanodontids were monophyletic in that they descended from a common ancestral line not shared with any other ornithopod group. Tenontosaurus (Ten-non-toe-sawr-us), occurring 115-108 mya was the most basal iguanodontian. In fossil finds, the presence of medullary bone was found in a thigh and shin bone that for today is only found in female birds when producing eggs.

Artist: H. Kyoht Lutterman Muttaburrasaurus

An ornithopod trending towards the iguanodontid form was, Muttaburrasaurus (Phonetics: Mut-tah-buh-rah-sawr-us) that occurred ~ 105.8 mya in the Early Cretaceous was basal to iguanodonts and is a member of an iguanodontid clade. Its skeletal anatomy is close to that of iguanodontids, but it was incapable of quadrupedalism and had teeth for slicing and shearing instead of the iguanodontid battery of teeth for chewing.

In taxonomic nomenclature, the term, Iguanodontoidea (Ig-wan-o-don-toy-dee-uh) is a ‘superfamily’ ranking that is not as specific as ‘family’ phylogenies. Whenever in dealing with animal taxonomy the suffix, ‘oidea’ refers to a superfamily. As an iguanodontoid, in today’s terms means it could be an iguanodon, but not quite yet there. This is the case for, Barilium (Ba-ril-e-um) that occurred 140 mya in the Early Cretaceous. Given its divergent phylogenetic position, it’s been separated out from the Iguanodon genus. It was a very stocky, even chubby dinosaur set with large vertebrae featuring short stubby neural spines to support the body weight. The hind limbs were almost elephantine with the distal pes covering a broad surface area.

Artist: Mark Witton Barilium

Above is paleontologist, Mark Witton’s interpretation of Barilium with folded and thick leathery skin; a contrast in dinosaur interpretations in always having smooth skin. The animals below Barilium are not birds but tiny maniraptoriform dinosaurs.
Artist: Mark Witton Iguanodon

A derived iguanodontid form was Iguanodon (Ig-wan-o-don) with a temporal range of 126-125 mya during the Early Cretaceous. Growing as long as 13m/43ft in length, Iguanodon was also bulky at 3.08 tonnes/3.4 tons in weight. The forelimbs were 75% the length of the hind limbs and walked both as a biped and quadruped as evidenced by fossilized footprints. Tendons were ossified along the neural arches facilitating both modes of pedal movement in absorbing most of the stresses incurred in bipedalism. This ossification limited backbone mobility in exchange for reinforcement. All of the cervical vertebrae had the ribs attached.

Iguanodon fossil

In the forelimb manus (hands), they were almost as useful as primate hands. Digits II, III and IV were close together where III and IV may have been bound together. Digit I (thumb), as opposable, was essentially a spike. Nevertheless, the manus would have been capable of grabbing. There can only be conjecture on what the spike was used for. It could have been used for gouging in defense from predation and intraspecific competition, or for males positioning the females during mating, or for all three conjectures. Skull muscle attachments suggest it had a large tongue.

Artists: Ray Moller/Dorling Kindersley manus (hands) 

Iguanodontids rapidly evolved into hadrosauriforms leading to hadrosaurids. The transition was so rapid on a geologic scale that Lurdusaurus’s (Lur-du-sawr-us) snout was becoming duck-billed, while Altirhinus’ (Al-ti-rain-us) snout was hollowing.

A few iguanodontids below:
Artist: Sergey Krasovskiy Altirhinus
Artist: Elperdido Lurdusaurus
Credit: Tenontosaurus

Hadrosauridae: Called the ‘duckbilled dinosaur’ due to the snout shaped similarly as a duck’s bill, did not possess any type feathering as other ornithischians had as all the innumerable hadrosaur skin impression fossil finds show only scalation of the skin. The snout rostral bones were flattened, thick and laterally compressed. There are three subfamilies of hadrosaurids being: Hadrosaurinae (Had-row-sore-e-nye), Saurolophinae (Sore-o-lop-phee-nye) and Lambeosaurinae (Lam-bay-o-sore-e-nye). Assumed for mating or alarm calls, lambeosaurines possessed hollow cranial crests/tubes made from the premaxilla and nasal bones that would sound once the animal exhaled through the nostrils. Hadrosaurids are considered facultative bipeds with most young walking bipedally while adults were mainly quadrupeds. Jaw design was to grind vegetation to a pulp aided by multiple rows of teeth that were replaced once worn down. Although solid crests were found in some of the species two subfamilies, most hadrosaurines and saurolophines did not support cranial crests; only lambeosaurines had hollow crests used for bellowing.

Artist: Julius T. Cstonyi Ouranosaurus
Living 86-66 mya, hadrosaurids are descended from iguanodontids with the few major differences being in iguanodontids having a larger maxilla bone in the upper jaw while hadrosaurids had the larger premaxilla in the upper jaw and a more complexed teeth arrangement. Hadrosaurid species sizes ranged from 3-12m/10-40ft. Ouranosaurus (Oar-ran-o-sawr-us), a hadrosauriform that lived 125-112 mya is considered a main stem line offshoot of iguanodontid evolution, but still closely related to hadrosaurids, in particular due to its skull anatomy and flattened snout.
Ouranosaurus skelatal anatomy
Ouranosaurus was unique in having a ‘sail’ type backbone supported by large neural spines down the dorsal topside of the animal that became thicker and more flattened at the distal end. The function is not clear, but besides used for thermoregulation or a display feature, one interesting idea is that it carried a hump much like a camel for storing fat during lean times. The spine arrangement stiffened the back primarily due to the posterior spines bound by ossified tendons.
Artist: Willydynamo Maiasaura nesting

Artist: Brian Switek Maiasaura hatchlings
Artist: Oliver Volland Maiasaura parental care

Maiasaura (May-uh-sawr-uh) literally means ‘good mother’ in reference to a fossil find composed of Maiasaura eggs, embryos and young found in a nesting colony. This supports parental care in at least the mother feeding the young in gathering fruit and soft plants. Mothers were too large to sit on nests without breaking the eggs, so as crocodilians, placed fermenting vegetation on top of the nest to provide heat as the plant material rotted. In rookeries, chances of egg and young survival were improved with the amount of gathered adults.
Artist: NestieBot Shantungosaurus

The largest hadrosaurid was Shantungosaurus (Shan-tun-gui-sawr-us) with a skull size of 1.63m/5.3ft and length of 16.6m/54ft. The beak was toothless but the jaws were packed with ~ 1,500 teeth made for chewing. A large hole near the nostrils is found in the fossils and is conjectured to have been covered by a loose flap of skin for bellowing. Shantungosaurus temporal range was in the Late Creatceous 78-74 mya.

Artist: Mihai D. Dumbrava Telmatosaurus

The smallest hadrosaurid was the 5m/16ft, Telmatosaurus (Tul-non-toe-sawr-us), a basal hadrosaurid living 70-66 mya. It lived on Cretaceous Europe’s Hateg Island where dinosaur species grew smaller due to insular dwarfism as discussed earlier under sauropods. Of interest here is that a Romania Telmatosaurus fossil gave pathological evidence of ameloblastoma that is today a rare nonmalignant tumor which usually develops in the jaws near the molars.

A few more of hadrosaurids:
Artist:Masato Hattori Mukawaryu recently discovered 2013

Artist: Luis V. Rey Charonosaurus
Artist:Victor Leshyk Gryposaurus
Artists: L. Xing/Y. Liu Lambeosaurus

Artist: Luis V. Rey Various hadrosaur heads

Marginocephalia: Dinosaur groups under Marginocephalia were all herbivores existing from 156-66 mya. Some were the last of the dinosaurs to live just prior to the Cretaceous/Paleogene extinction, but all became extinct during and just after the event. These ornithischians as grouped into the two subgroups, pachycephalosaurians and ceratopsians are best known as the ‘bone head’ pachycephalosaurians and the ‘horn faced’ ceratopsians, like the three horned Triceratops (Tri-sair-ah-tops). But, Triceratops was just one species of many dinosaurs under the family, Ceratopsidae (Sair-ah-top-see-day). There are three subfamilies under Ceratopsidae and at least forty-four genera. Pachycephalosaurians were bipeds and are the one herbivorous dinosaur group that never trended towards quadrupedalism. The earliest basal ceratopsians and Psittacosaurid ceratopsians were facultative bipeds, while all other ceratopsians were quadrupeds, with the exception of the bipedal, Archaeoceratops (Ar-kay-oh-seh-rah-tops). The predentary and rostral supported a horny beak in all marginocephalosaurians.   

Marginocephalians first evolved in the Late Jurassic 156 mya and thrived until the end of the Late Cretaceous 65.5 mya, thus being one of the last groups of dinosaurs to go extinct. All the earlier forms, or primitive marginocephalians originated in what is now the Asian continent, with the later and more derived migrating up into what is now North America.

Marginocephalians were social creatures and through fossil evidence roamed in small to large herds and formed rookeries for their eggs and hatchlings. They also herded with other dinosaur groups. There is evidence as well of interspecies communication implying cooperative communication between other species and with this sharing and understanding, formed a mutualism factor that benefitted all species concerned. This spurs the idea that interspecific communication in the transfer of information, whether by language or sight signaling is yes, first a learned trait, but is through an evolutionary mechanism.                 

Pachycephalosauria ~ Living at the end of the Early Cretaceous to the end of the Late Cretaceous 99-66 mya, pachycephalosaurians are known for their thickened cranial skull caps. There is debate on proper mobility, but they were bipeds and could casually walk on all fours at times such as grazing on low vegetation. However, pachycephalosaurians are the one herbivorous dinosaur group that never trended towards quadrupedalism. Most pachycephalosaurians were small, averaging 2-3m/6.6-9.8ft, but as most small dinosaurs were, they were not climbers, instead were limited to accessing food no higher than one meter above the ground.

In terms, the order, Pachycephalosauria and the family, Pachycephalosauridae were studied and reevaluated in 2006 and from that, it was determined that they both included the same species taxa. As a result, it was concluded that Pachycephalosauria was redundant and struck its ordering leaving only Pachycephalosauridae to list all pachycephalosaurians and pachycephalosaurs into the one family group. But this groups all less bony flathead and bonier dome head pachycephalosaurs into one family. I disagree with that; but who am I, right? Anyway, since the flatheads were more primitive and older than the more derived bone heads, along with other anatomical, even physiological differences, I feel that the group, Pachycephalosauria and its immediate basal ancestors should remain and that is why I’m presenting it as such. Just to inform ya, so enough stated...
Artist: Cisiopurple Wannanosaurus

I’m listing Wannanosaurus (Wan-nan-oh-sawr-us) here as a primitive pachycephalosaurian basal to pachycephalosaurids. In today’s literature it most likely will be listed as a pachycephalosaurid. Occurring in the Late Cretaceous 80 mya, Wannanosaurus was a tiny at 60cm/24in and supported a flattened skull with large fenestrae. The fossil find gives evidence of fused bones determining that it was an adult. It may have also supported some dorsal quilled feathering. According to dentition, it most likely was not a strict herbivore as later pachycephalosaurids were, but was omnivorous in dieting on plant material and insects.         

Pachycephalosauridae: Due to combining both pachycephalosaur groups into one, this family contains eighteen genera of pachycephalosaurs, but due to the uncertainties in the polarities of species characters, makes for a less cladistic analysis. There is also ongoing debate as to if the flatheads were simply subadult forms of the domed boneheads. The temporal range was in the Late Cretaceous 76-65.5 mya. The revised definition of pachycephalosaurids is among other traits, those marginocephalosaurians with thickened but fully flat to fully domed frontoparietals (frontal and parietal bones of the cranium), the squamosal was a deep plate on the occiput having enlarged upper-outer corners, the premaxillary-maxillary diastema was arched and possessed developed rows or clustered nodes or blunt horns on the squamosal, nasals and in species specificity, other parts of the skull.

Concerning the domed boneheads, it was first interpreted that the thickened skull was for intraspecific combat in head butting or for interspecific defense against predators. This idea was bolstered through dome head cranial histological studies where 22% of all domes examined had healed lesions consistent with osteomyelitis, an infection of the bone resulting from penetrating trauma. In flatheads there was 0.00% of any head trauma, which supports the subadult flathead thesis as mating combat is performed only by adult males.

The bone tissue of the domes was composed of a unique form of fibrolamellar material containing fibroblasts that play a critical role in bone healing. This further accelerates the proponents’ idea of pachycephalosaurid ‘agonistic behavior’ defined as any social behavior related to fighting. Also, to aid in absorbing the head-butting blows, the spinal column possessed vertebral articulations providing spinal rigidity. However, pachycephalosaurids carried their necks in U or S shaped curves and could not step back and charge each other with straightened necks spread out horizontally for head on butting.
Artist: De Agostini

Pachycephalosaurids’ head, neck and spine could not align itself in such a way as to absorb, alleviate, or transmit stress like an extant musk ox or mountain goat can today. In addition, domed head butting would for the most part result in glancing blows due to the curvature. This would’ve created much more damage to the head due to the nodes and clusters of small horns (spikes) creating open wounds to the domes’ skin or keratinous coverings and other parts of the head that would have created serious infections. As well, to reduce weight, the fibrolamellar material was spongy and would crush under the force of head on butting.

So, I support the side that feels, although pachycephalosaurids weren’t head bangers, they did indeed use the domes for intraspecific ‘flank butting’ that would allow the domes to give a bruising side blow to an opponent’s hindquarters, but still not do too much damage to the head. For sure the domes evolved as weaponry and not as species identification, for all pachycephalosaurid domes were indistinct in anatomy and appearance.
Artist: Nobu Tamura Homalocephale

Credit: Goyocephalae
The two flat heads listed as primitive pachycephalosaurids are, Homalocephale (Hom-ah-loh-sef-uh-lee) and Goyocephalae (Goi-uh-sef-uh-lee). Both of these pachycephalosaurids had very small forelimbs, a triangular shaped skull and stiffened tails supported by bony rods called zygapophyses that was an articulated paired process fitting one vertebra to its adjacent vertebra. Both also had, along with oral leaf-shaped teeth further back in the mouth, canine-like teeth in the front of the mouth. Homalocephale, occurring in the Late Cretaceous 80 mya had a very broad pelvis that was most likely positioned as such to protect vital organs from flank butting. It was 1.8m/6ft long. Goyocephalae occurred 76 mya in the Late Cretaceous and was also 1.8m/6ft in length. Its canine-like fangs were not serrated, but with the heterodontosaurid, Heterodontosaurus tucki retaining similar canines, heterodontosaurids and pachycephalosaurs share common ancestry.

Dracorex skeletal anatomy
Artist: Darren Horley Dracorex
Dracorex (Dray-core-ex) was another flathead, but due to its temporal range of 66 mya near the end of the Late Cretaceous, there is referral to it as being a subadult of Pachycephalosaurus that hadn’t yet developed the bony dome. The fossil consists only of the skull, so it’s very difficult to check for total bone fusion and ossification in determining if it was an adult or juvenile. However, this specimen had a huge pair of supratemporal fenestrae unlike Pachycephalosaurus and more like the much earlier flatheads. So Dracorex could have simply been an earlier form of flathead that had a much longer temporal range. The flat cranium supported spiky horns, knobs and a long muzzle, thus the name referring to ‘dragon king’.

Artist: Vlad Korstantinov Pachycephalosaurus

The last two pachycephalosaurs to go extinct were the pachycephalosaurids, Pachycephalosaurus and Sphaerotholus (Sfay-ro-fo-luss) with a Late Cretaceous temporal range of 70-66 mya and 73-66 mya respectively. Both are considered the most highly derived of all pachycephalosaurians. While the three genera of Sphaerotholus lengths are unknown due to lack of body fossil material, size probably averaged no more than 2.4m/7.9ft. As for Pachycephalosaurus, it so far is the largest pachycephalosaur at 4.5m/14.8ft.

Artist: FishPainter Sphaerotholus

Some pachycephalosaur pics:            
Artist: Julius T. Cstonyi Acrotholus

Artist: Dinoraul P. wyomingensis
Credit: Paleo-World Prenocephale

Artist: Cisiopurple Various pachysaurs

Ceratopsia ~ Although ancestral forms lived as far back as 161.2 mya in the Late Jurassic, the bulk of ceratopsians lived during the Cretaceous Period. As in pachycephalosaurians, the main feature in ceratopsians was in the skull’s bony ornamentation. Ceratopsians eventually embellished on the skull ornamentation, but instead of bony domes and small spikes, they elaborated on frills and horns.

Unique to ceratopsians, the rostral bone located on the tip of the upper jaw anteriorly joins the two premaxillae forming a single midline bone. The modification represents an upper jaw mirror image of the predentary and like the predentary the rostral also supported a horny beak. The jugal skull bone pointed laterally to form a horn-like process.      

Essentially there were two main evolvement influences within ceratopsians during the Cretaceous. The first evolution sequence involved psittacosaurs (121-99 mya) giving rise to Protoceratops (Pro-toe-sair-ah-tops) 83 mya. In turn, Protoceratops gave rise to Styracosaurus (Sty-rah-co-sawr-us) then to Triceratops (Tri-sair-ah-tops) 67 mya.

Ceratopsians are further divided into Neoceratopsia, Leptoceratopsidae, Ceratopsoidea and Ceratopsidae. Exclusive neoceratopsians are comprised of nine individual genera and three families with their own genera species. Ranked underneath neoceratopsians is the superfamily, Ceratopsoidea, with two genera species. Further under ceratopsoids, is the ceratopsids under the family, Ceratopsidae. It consists of three subfamilies, Centrosaurinae (Sin-tro-sawr-e-nay), Ceratopsinae (Sair-ah-tops-e-nay) and the largest neoceratopsian group of all is the ceratopsid subfamily, Chasmosaurinae. (Kaz-mo-sawr-e-nay).
Artist: Cheung-tat Chung  Yinlong

Artist: Danny Cicchetti Stenopelix
Yinlong (Phonetics: Yin-long) and Stenopelix (Sten-oh-pel-ix) were both basal to primitive ceratopsians. Living in the Early Cretaceous 158 mya and 127 mya respectively, they are sister taxons. Yinlong is the earliest and most primitive of ceratopsians. It was 1.2m/3.9ft in length and was a bipedally mobile herbivore. The hornless skull had a raised ridge base that was not quite yet considered a frill.  Stenopelix was an herbivore and small at 97cm/38.2cm. The pelvis was ceratopsian with the ilium’s shaft uniformly tapering into a rounded point, while the ischium’s shaft was thickest in the middle forming a kink.      

One of the older and first successful ceratopsians to appear was in the family, Psittacosauridae (Sit-tah-coe-sawr-ah-day). Due to their beaks, psittacosaurids are known as the ‘parrot lizards’ and occurred in the Early Cretaceous 126-101 mya. Psittacosaurids first arose in Asia placing all the ceratopsian groups having their ancestral origins from Asia. Rather small, the largest in, P. mongoliensis (mon-go-lie-in-sis) was 2m/6.5ft in total length, while P. ordosensis (ord-o-in-sis) was 2.4m/4.6ft.

Artist: Nobu Tamura Psittacosaurids 

Psittacosaurid skulls were frill-less and hornless, but in more derived species, bony lumps on the skull were evident serving as a precursor to later ceratopsid horned ornaments. Juvenile fossils suggest they were quadrupeds while transitioning into obligatory bipeds as adults. The adult forearms could not rotate nor add lift in springing forward giving more indication of a bipedal gait.

Psittacosaurid stomach stones

Dentition was adapted for slicing through plant food and due to studies of psittacosaurid teeth, the teeth arrangement and particular wear validates that the teeth sharpened themselves. Evidence also alludes to a seed rich diet as gastroliths have been found in psittacosaurid fossil sites in the gut area.

Psittacosaurid fossil Note: tail feathering integuments

There are plenty of psittacosaurid fossils showing long quill impressions that were located on the dorsal rear and caudal base of the animal. The quills would not have served as insulation, so were probably for display purposes only. These preserved quills were tubular bristle-like structures more likely with a keratinous covering and extended through the skin almost to the vertebrae. From China’s Yixian Formation, psittacosaurid fossils even give evidence of feathering as observed by the studies.

Artist: Robert Nicholls Psittacosaurus sp.

Psittacosaurid integument (body covering) in fossil finds shows the body covered in small scales with larger scales dispersed in irregular patterns. For camouflage purposes there were counter shading with the top of the body exhibiting darker melanism than the ventral portion, which was a much lighter tannish brown. This suggests a livelihood in forests or a region with a thick canopy.
Psittacosaurid fossil family

Due to the innumerable fossil finds, from embryos to adults, psittacosaurids have been found in all their life stages. From studies, hatchlings with longer forelimbs in relation to the shorter, stubbier hind limbs would’ve been skilled crawlers. Although by five years of age, the hind limbs underwent a massive growth squirt catching up to and surpassing the forelimbs. By six years of age, psittacosaurids were facultative bipeds.

Psittacosaurid fossil of six juveniles

In the above photograph is a group of six young psittacosaurids huddled together while being buried by a volcanic mudflow. We know that they were alive at the time of burial because of all the heads were raised. This huddled mass of psittacosaurids is not representative of a nest but of gregarious behavior extending beyond the nest. Based on histological analysis, specimen 1 was three-years-old, with specimen 2-6 being only two-years of age. Most likely they were huddled for security due to the fear of the oncoming onslaught that ended their lives.   
Artist: Kana Hebi Leptoceratops

Artist: Nobu Tamura Cerasinops
Neoceratopsia ~ was the sister group to Psittacosaurus. Neoceratopsian subgroups temporal range was from 99-66 mya in the Late Cretaceous. This major clade includes the most derived ceratopsians which for the most part is the horned ceratopsians. The side neoceratopsian family, Leptoceratopsidae (Lep-toe-sair-ah-tops-ah-day) was the more primitive group in this clade and members were hornless. One leptocertopsid, Cerasinops (Seh-rass-e-nops) was psittacosaurid-like but details more of a transitional primitive basal neoceratopsian.
Artist: Lukas Panzarin Koreaceratops

Another primitive neoceratopsian was, Koreaceratops (Koe-ree-ah-sair-ah-tops) that appeared towards the end of the Early Cretaceous 103 mya. It is notable for its caudal vertebrae’s tall neural spines that were five times the height of its back’s midpoint vertebral centra. These spines have shown up in several other ceratopsians, such as Bagaceratops, Montanocertops and Udanoceratops, but seems to have independently evolved. Koreaceratops’ astragalus (talus or ankle bone) structure was also unique in that it divided into two fossae (Fossa is a bone depression) by a prominent craniocaudal ridge on the proximal surface. These characteristic features point to a semi-aquatic lifestyle for swimming capabilities.
Artist: Brian Engh Aquilops bothered by a mammal
Aquilops occurring 107 mya in the Early Cretaceous is currently one of the oldest neoceratopsians thus found. It is also the oldest and most basal neoceratopsian found in Cretaceous N. America. Neoceratopsians first evolved in Asia. With Aquilops already established in N. America, it’s indicative of an early migration from Asia to N. America. Crossing land bridges before the full rifting apart of Gondwana into new land masses, Aquilops’ Asian neoceratopsian ancestors migrated to N. America late in the Early Cretaceous. As a neoceratopsian, Aquilops was closer in relations to Triceratops than to Yinlong.

The most primitive of neoceratopsians are in the family, Leptoceratopsidae that had a temporal range of 83.5-66 mya in the Late Cretaceous under ten genera. Leptosaurids evolved in what is now Sweden and once during the Late Cretaceous’ Campanian Stage (83.6-72.1 mya) when N. America became isolated from northwestern Europe due to continental drift, creating endemic forms in eastern N. America. The bulk of leptosaurids however originated from Asia and Western N. America.
Artist: Kana Hebi Montannoceratops 

Leptoceratopsidae means ‘small horned face’, but despite the name, leptosaurids had no horns. With species no more than 2m/6.56 long, leptosaurid dentition set them apart from other neoceratopsians in having massive robust jaws supporting huge bulbous teeth. This surely was their adaptation for survival as they would never starve or be out competed for food sources because they were able to ingest the toughest of plants assimilated for digestion by their grinding and pulverizing teeth. Two leptoceratopsids species in, Montanoceratops which lived 70 mya and Leptoceratops (Lep-toe-sair-ah-tops) occurring 66.8-66 mya both had short, deep and muscular jaws creating a strong bite and high masticating abilities. They both possessed claws on the distal ends of the manus (hands) and pes (feet) and also both could move as a quadruped or bipedally.  
Artist: Sergey Krasovskiy Turanoceratops
Turanoceratops (Tu-ran-o-sair-ah-tops), although with too numerous primitive features to be a true ceratopsid and after numerous cladistic debates, has been put into the superfamily, Ceratopsoidea (Sair-ah-top-soi-dee-uh). This put Turanoceratops, as basal to ceratopsids, in representing a transition from ceratopsians to ceratopsids. At 2m/6.6ft in length, its paired horns formed from the base of the frill pointed anteriorly over then beyond the eyes. Turanoceratops is the only ceratopsoid member found outside N. America. Its remains were discovered in Uzbekistan in 90 million year old Late Cretaceous strata.

Artist: Walter Colvin Zuniceratops

Another ceratopsoid and the first horned ceratopsian to appear in N. America was Zuniceratops (Zoo-nee-sair-ah-tops). The skull supported two horns above the eyes called ‘brow horns’ and a thin, broad frill that acted as a shield in protecting the back of the head and neck. The frill had two large openings in the middle that were covered by skin and keratinous scaling. Not exactly useful in predatory protection, the fenestrated frill would have been lighter and was most likely used for display.   

Occurring 91 mya during the Late Cretaceous, it was about the same size of a large cow at 3-3.5m/9.8-11.5ft in total length. In juveniles, the dentition was single rooted, but with age in adults, the dentition became double rooted. Whether direct or indirect through ancestral lineage, Zuniceratops’ line is what led to the N. American, Ceratopsidae groups making both families a sister group.          

As a sister group to ceratopsoids, the family, Protoceratopsidae (Pro-toe-sair-ah-tops-ah-day) occurred 85-72 mya in the Late Cretaceous. This was too late to be a direct descendent to ceratopsids, but as a younger sister group to the older ceratopsoid clade, they were more like an aunt to the most derived ceratopsians in the family, Ceratopsidae.

Artist: Luis V. Rey Protoceratops
Protoceratopsids at an averaged 1.8m/5.9ft long were about the size of a goat. They had an established fenestrated light frill. In some species, the frills were short and compact while in others the frills were at least half the length of the skull. The frills consisted mostly of the skull’s parietal bone, but also contained components of the squamosal bone. They retained the psittacosaurid caudal quills, although protoceratopsids were fully bipedal, but still with shorter forelimbs. Indicating a nocturnal lifestyle, protoceratopsids had large orbits (eye openings) that housed a small fenestra behind each eye known as the infratemporal fenestra. The neck vertebrae were limited to lateral mobility arranged more for vertical up/down motion. The jaws were packed with dozens of teeth and with powerful jaw muscles and a massive frontal beak protoceratopsids were well adapted to chewing rough plants and delivering an injurious bite for defense. Protoceratopsids were hornless.

Artist:Maspix Protoceratopsid herd in arid terrain
As fossil sites attest to, protoceratopsids were a herding animal and with the males being larger in height, width and possessing larger skulls and frills practiced sexual dimorphism. The frill may have been colorfully decorated for attracting mates. The larger and colorful frills probably induced the males to head bob one another and if that wasn’t a competitor deterrent would engage in head pushing for dominance.
Artist: Raul Martin Protoceratops/Velociraptor dueling
Protoceratopsids lived in desert or dry environments. From paleo-Mongolia, paleontologists came upon an exciting find with P. andrewsi (an-drew-see) in mortal combat with Velociraptor mongoliensis. Apparently, this scene during life was suddenly covered up by a sand slide or strong sandstorm burying and killing both animals in their life and death struggle, but preserving it as well. If played out, the outcome looked like the velociraptorine predator was getting the short end of the stick.

Protoceratops/Velociraptor combat fossil 
A few more of protoceratopsids:
Artist: Antonin Jury P. andrewsi
Artist: Vlad Konstantinov a young Protoceratops
Artist: Vlad Konstantinov P. sibiricus

Ceratopsidae: This family group of skull horned and large frilled neoceratopsians appeared in the Late Cretaceous 83-66 mya. The horns were located on the nose and just above the eyes. With Triceratops reaching lengths of 7.9-9.0m/25.9–29.5ft and Eotriceratops topping out at 8.5m/27.9ft, ceratopsids were the largest of all ceratopsians. These dinosaurs were the Late Cretaceous version of vast herds of grazing bison on the midwestern N. American plains, except for the fact that western paleo-N. America during the Late Cretaceous wasn’t grasslands, but coastal plain marsh lands on the Western Interior Seaway with a subtropical climate and numerous small rivers and large streams.

The large frills were also ornamented differently in each species and changed in ornamentation within each species maturation age from juvenile to subadult to adult. Honors for the most elaborate frill likely goes to, Kosmoceratops. It had a row of ten small horns rimming the frill with the middle eight curving inwards. This ceratopsid was isolated on a restricted island in the Western Interior Seaway. The isolation diminished gene pool influxes from other parts of N. America allowing Kosmoceratops to evolve on its own. Once the seaway began receding southwards due to Rocky Mountain chain orogenic uplifting, Kosmoceratops intermingled with other diversified gene populations and lost its unique identity.

Artist: Lukas Panzarin Kosmoceratops
Ceratopsids are divided into two main subfamily groups the, Centrosaurinae (Sin-tro-sawr-ah-nay) and Chasmosaurinae (Kazz-mo-sawr-ah-nay). The key difference between the two was that in centrosaurines had a large nasal horn and two short supratemporal horns, where it was the exact opposite in chasmosaurines in having long supratemporal horns and a short nasal horn. There are currently 18 genera under the subfamily, Centrosaurinae and 23 genera under the subfamily, Chasmosaurinae.     

Other derived characteristics of these two subfamilies listed as one (1) and two (2) in the cladogram below are defined as (1) Chasmosaurinae: enlarged rostral, presence of an interpremaxillary fossa, triangular squamosal epoccipitals (small spikes or horns rimming the frill), rounded ventral sacrum, and a broadly decurved  ischial shaft. (2) Centrosaurinae: premaxillary oral margin extending below alveolar margin, jugal infratemporal flange, squamosal much shorter parietal, six to eight parietal epoccipitals and predentary biting surface steeply inclined laterally.

Speaking in geological timeframe terms, ceratopsids in general evolved rapidly and simultaneously into their most derived forms, whether genetically or through convergent evolution. As expressed in the above graph, once centrosaurines became extinct, chasmosaurines began evolving through convergence via centrosaurine horn characteristics and is proven through the 68.5-67.5 million year old chasmosaurine, Regaliceratops. This 5m/16.4ft long chasmosaurine became transitional in the skull’s horn morphologies by evolving a large centrosaurine-like nasal horn with shorter supratemporal or ‘brow’ horns.

Artist: Luis V. Rey Einosaurus
A unique centrosaurine was, Einiosaurus (Phonetics: Eye-nee-o-sawr-us). Its temporal range was in the Late Cretaceous 74.5-74 mya. It also had some transitional skull features akin to chasmosaurines. Among other ceratopsids, frill structures and the skull of Einiosaurus were evolving into elaborate ornamental displays. The nasal horn curved forward pointing towards the ground, while the two supratemporal horns encased in the small frill and epiparietals (frill horns) pointed backwards. From encircling the eyes to rimming the frill there was a continuous row of osteoderms. From evidence of multiple individuals in fossil remains Einiosaurus herded.

Artist: Vlad Konstantinov Triceratops
The classic chasmosaurine, Triceratops, weighed 10.9 metric tons/12 US tons. With remains found all over N. America and in particular out west, the first discovery near Denver, Colorado in 1887, it was first thought to be some specialized buffalo. Unlike most ceratopsids, Triceratops was more of a loner and did not herd in large groups as most fossil finds are of individuals and not groups.
The chief predator to Triceratops was Tyrannasaurus rex as evidenced through the multiple fossil finds of T. rex gnaw marks on Triceratops fossilized bone and actual T. rex teeth embedded in or lying near Triceratops fossils. A Montana fossil site unearthed in 1997 showed a Triceratops skull with cone-shaped indentations matching the tooth tips of a typically large T. rex. In addition, on the left side of the skull were gaps between three deep parallel scrapes which also match the tooth spacing of T. rex which was the only large predator in the region during the ending of the Late Cretaceous. The healed skull scars first show signs of infection then healing, proving that the ceratopsid survived the encounter. But whether it won in the battle or was lucky enough to get loose and run off, we’ll never really be proven. In Triceratops/T. rex battles, we’ll go into more detail later under, ‘Theropoda’.

Artist: Luis V. Rey Triceratops vs. T. rex
Living in the Late Cretaceous 72-71 mya, Anchiceratops (An-chi-sair-ah-tops), is considered a transitional and intermediate ceratopsid form closely related to both, Monoclonius (Mon-oh-clo-nee-us) and Triceratops (Tri-sair-uh-tops). Fossil remains have been found in terrain sediment, but in Alberta’s lower ‘Horseshoe Canyon Formation’, where numerous fossils of it have been found is composed of shallow marine coastal sedimentation, coal swamps, floodplains, brackish water deposits from periodic seawater incursions into estuary channels, estuarine point bar deposits, carbonaceous shales, mudstones and sandstone freshwater sediment. From this, it can reasonably be interpreted that Anchiceratops was hippo-like in foraging aquatic plant material. Another trait to allude to this conclusion is in this chasmosaurine’s skeletal anatomy featuring a much longer pelvis, more robust forelimbs and shorter tail than other ceratopsids.
Artist: Craig Dylke Anchiceratops
Some more pictures of ceratopsids:

Credit: Phil Tippets' 'Prehistoric Beast' Monoclonius

Artist: Julius T. Cstonyi Regaliceratops

Artist: Nobu Tamura Centrosaurines
Artist: Nobu Tamura Chasmosaurines

Due to the lengthiness, Dinos 2 will be completed with the story of theropods and birds in the next article of ‘Et Tunc Nulla Erat IX’.

Hoping Every One had a Fun Holiday Season, in Spite of Trump!
Oct 2017-Jan 2018