Triassic Reptile Shows Example of Convergent Evolution with Dinosaurs

A team of scientists including researchers from Virginia Tech College of Science and the University of Chicago have identified a new species of Triassic archosaur (potentially), one that shared some remarkable anatomical characteristics with its much later and very distant relatives, the bone-headed dinosaurs.  The little reptile, fossils of which were excavated from Upper Triassic chalk deposits in Howard County (Texas, USA), has been named Triopticus primus, it’s skull shows a similar shape and morphology to the much later, Late Cretaceous pachycephalosaurid dinosaurs, animals that lived more than 100 million years later.

Triopticus primus

A Graphical Representation Showing Convergence Between Triassic Archosaurs and Later Archosaurs (Dinosauria)

Triassic archosaurs showed striking similarities to later archosaurs.

Picture credit: Current Biology

Similarities in body plan evolution are relatively common place in the history of animal life on our planet.  For example, the wings of pterosaurs, bats and birds are superficially similar as they are all adapted to providing powered flight.  Icththyosaurs and dolphins have very similar shaped, streamlined bodies, adaptations to a nektonic marine existence.  Surprisingly, the researchers identified numerous additional taxa in the fossil deposits of Howard County (Otis Chalk assemblage from the Dockum Group of Texas), that demonstrate the early acquisition of morphological novelties that were later to appear in other members of the Archosauria, most notably the Dinosauria.

Dominating Terrestrial Environments

Developing similar body plans in Triassic archosaurs, comparable to those seen in later members of this extensive reptilian group, for example, the Dinosauria is not all that of a turn up for the books, when you consider it.  Towards the end of the Triassic the Archosauriformes had established themselves as the dominant terrestrial vertebrates, a position that one specialised group of archosaurs, the Dinosauria, were to take up and not relinquish for another 150 million years or so.

For models and replicas of dinosaurs and other archosaurs: Mojo Prehistoric and Extinct Figures.

A number of authors have challenged some of the conclusions from the paper entitled “A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives”, nesting Triopticus primus within the basal Archosauriformes as in the paper, is not without its controversy.  The skull is very different from other archosaurs.  It is only until the likes of the pachycephalosaurid Stegoceras appears in the Late Cretaceous, that archosaurs with such expanded craniums that lack an upper temporal fenestra, that a skull shape like Triopticus is seen again.

Corresponding Author of the Scientific Paper Michelle Stocker and a Cast of the Triopticus Skull

The skull of the bizarre Late Triassic reptile Triopticus.

Picture credit: Virginia Tech College of Science

Controversial Taxonomy

Although the exact taxonomic affinity of Triopticus is controversial, the Otis Chalk deposits may reveal more examples of convergent evolution.  If Triopticus is classified as a member of the archosaur group, then its fossils may demonstrate that some types of dinosaur evolved body plans very similar to their Triassic-aged relatives.  If this is the case, then early evolution of body plans may have constrained later archosaurs in the type of body plans that they could evolve.

Whatever the relationship to archosaurs, Triopticus primus evolved a very thickened skull, quite what for remains a mystery.

It Looks Like Pachycephalosaurs were not the First “Bone Heads”

A lithe Pachycephalosaurus dinosaur model.

Picture aredit: Everything Dinosaur

Visit Everything Dinosaur’s website: Everything Dinosaur.

You Have Just Got to Hand it to Drepanosaurus unguicaudatus

A team of international scientists including researchers from a number of eminent American scientific institutions (Stony Brook University, The Dinosaur Institute at the Los Angeles County Natural History Museum and the Natural History Museum of Utah, have published a remarkable description of a Late Triassic, diapsid reptile that overturns the rule book when it comes to tetrapod limbs.

Writing in the journal ” Current Biology”, the small-bodied, possible arboreal, reptile called Drepanosaurus unguicaudatus had the most astonishing forelimbs, the configuration of the bones that make up the forelimb are quite unlike anything previously seen.

Forelimb Specimens of Drepanosaurus unguicaudatus from the Chinle Formation (New Mexico)

Forelimb specimens of Drepanosaurus unguicaudatus from the Zorzino Limestone and Chinle Formation.

Picture credit: Current Biology

Upsetting the Tetrapod Blueprint

Tetrapods, in essence all four-limbed vertebrates and that includes us, have shown remarkable consistency in the structure and anatomy of their limbs over the 375 million years or so since the very first tetrapods evolved (Late Devonian).  Tetrapod limbs may have become adapted for all sorts of functions, such as locomotion, climbing, swimming, digging or even manipulation of small objects via being able to pronate the limbs (something that we humans can do very well), but despite this enormous array or functions, the bones of the forelimb have remained largely unchanged.

Most tetrapods have parallel shafts of bone (the radius and ulna), in the forelimb.  The ulna is the medial bone, the radius is the bone furthest away from the centre of the body.  The forelimb bones of D. unguicaudatus are very different.

For replicas and models of prehistoric animals, take a look at the remarkable Rebor range: Rebor Prehistoric Animal Models.

Drepanosaurus unguicaudatus

Examination of a number of specimens excavated from a quarry that forms part of the Petrified Forest Member of the Chinle Formation of northern New Mexico, revealed that this Late Triassic reptile had a flattened, crescent-shaped ulna and shaft-like carpal bones.  The second digit (the index finger if you like), supported an enormous and strongly curved claw somewhat reminiscent of the claw on a Silky Anteater (Cyclopes didactylus).  It has been proposed that the bizarre Drepanosaurus lived in trees and used its long claw and strong arms to rake the bark and to prise insects out of cracks and crevices.

The scientists conclude that the forelimbs of this small reptile (it grew to about sixty centimetres in length, possibly a little more), were adapted to a “hook and pull” niche seen in extant arboreal animals such as the Silky Anteater.  This huge claw gave Drepanosaurus its genus name “sickle lizard”, the claw on the second digit was bigger than the whole of the rest of the hand.

One Very Bizarre Reptile

Named and described in 1979 from a single, badly crushed specimen found in Italy, Drepanosaurus may represent an “experiment” in tetrapod evolution, with this animal adapting to a very specific niche. How specialised Drepanosaurus was has only been revealed following extensive CT scans of more fossils, this time excavated from a site known as Hayden Quarry from northern New Mexico.

An Illustration of Drepanosaurus unguicaudatus

An illustration of the strong-limbed, scorpion tailed diapsid Drepanosaurus.

Picture credit: Victor Leshyk

Drepanosaurus has been described as having a bird-like head, on the body of a chameleon with a humped back (possibly to anchor strong back muscles), disproportionately oversized forelimbs and a long tail with a claw on the end (presumably to help the animal gain a grip on a tree branch).  We like to think of Drepanosaurus as a reptilian equivalent of Popeye!

What Would Darwin Think?

Charles Darwin used the similar anatomies found in tetrapod forelimbs to support his idea that all these animals shared a common ancestor.  This biological principle of common, shared traits is called homology. Charles Darwin argued that the consistencies found in the bones and their configuration in four-limbed creatures supported the idea of evolution.  We wonder what the great man would have made of Drepanosaurus?

Visit Everything Dinosaur’s award-winning website: Everything Dinosaur.

Giant Dinosaur Footprint from the Gobi Desert

The Upper Cretaceous formations of the Gobi Desert have provided scientists with a treasure trove of dinosaur fossil bones and teeth to study.  Trace fossils such as footprints are much rarer.  However, last month a joint Japanese and Mongolian research team uncovered a beautifully preserved natural cast of a giant plant-eating dinosaur’s foot.  The footprint, which represents the left hind foot of a titanosaur, is estimated to be between ninety to seventy million years of age and it was made by a dinosaur not currently known (most probably), from any bones within a museum’s collection.

Gobi Desert Fossil Discovery

The ancient, fossilised footprint was discovered as a joint research team from the Okayama University of Science (Okayama Prefecture, Japan) and researchers from the Institute of Palaeontology and Geology of the Mongolian Academy of Sciences explored exposed Upper Cretaceous sediments in the Gobi Desert.

Professors are a Great Way to Show the Size and Scale of Dinosaur Tracks

Professor Shinobu Ishigaki (Okayama University of Science) provides the scale for the dinosaur print.

Picture credit: Okayama University of Science

In the picture above Professor  Shinobu Ishigaki (Okayama University of Science),  is lying next to the giant footprint.  His head is towards the rear of the foot and clearly defined claw impressions can be seen on the front of the footprint.  The dinosaur was walking towards the left of the photograph (direction of travel).

The exact location of the fossil find is a closely guarded secret.  Unfortunately, despite strict laws, the illegal export of many dinosaur fossils from the Gobi Desert still occurs and there is a significant black market trade in such ancient artefacts.

Giant Dinosaur Footprint

The print was discovered on August 21st and it measures 106 centimetres long and 77 centimetres wide (maximum diameter).

Commenting on the importance of this discovery, Professor Ishigaki, the leader of the research team from the Okayama University of Science, stated:

“A whole skeleton of a giant dinosaur that left such a massive footprint has yet to be uncovered in Mongolia.  A fossilised skeleton of such a dinosaur is expected to be eventually discovered.”

An Illustration of a Typical Titanosauriform (Daxiatitan)

Perhaps up to 30 metres in length?

Picture credit: Everything Dinosaur

The picture (above) shows a titanosaur.  It is the sort of dinosaur that could have produced the giant dinosaur footprint.  The figure is a CollectA titanosaur model.

To view this model collection: CollectA Models (Prehistoric Life).

Estimating the Size of the Maker of the Track

Although it is not possible to give an accurate estimate of the dinosaur’s size, the individual who made this print may have exceeded twenty-five metres in length.  The print is a natural cast created by sandy sediments infilling the impressions in the ground caused by the dinosaur walking over a muddy substrate.

Commenting on this fossil find a spokesperson from Everything Dinosaur added:

“Titanosaurs are wide-bodied sauropods [long-necked, plant-eating dinosaurs] that probably evolved sometime in the Late Jurassic and survived until the Cretaceous mass extinction event.  They are the only sauropods known to have survived into the Late Cretaceous.  The exceptional preservation of this natural cast makes this discovery extremely significant.  The shape of the claws can be made out and even the texture of the bottom of the foot has been preserved.”

Trace Fossils are Important

Trace fossils are important as they preserve evidence of activity, as in this case the footprint of a huge, plant-eating dinosaur.  Not only does this track provide information on the shape of dinosaur’s feet but it also provides valuable information on the ways in which they walked.

To read about some even bigger sauropod tracks discovered in France: 150 million-year-old Sauropod Prints from France.

For an article about a probable new titanosaur from Brazil: A New Brazilian Titanosaur (probably).

To read an article published earlier this year about a new titanosaur from Argentina: New Late Cretaceous Titanosaur from Patagonia.

DNA Analysis Hints at Earlier Exodus of Modern Humans from Africa

A number of scientific papers have been published this week, most notably in the journal “Nature”, which discuss the thorny issue of how our species spread across the world.  Studies of modern human genomes from populations around the globe hint that there may have been an earlier human migration out of Africa, however, the evidence for this earlier migration remains controversial.

Understanding how and when our species migrated out of Africa and spread around the planet, reaching far-flung destinations such as Australasia, is still some way off.  Rather than clarify and unify theories, genetic studies seem to have muddied the waters somewhat.

Out of Africa Human Migration

A Native of Papua New Guinea – New Research Indicates A Very Ancient Human Ancestry

A native of Papua New Guinea.

Picture Credit: Eric Lafforgue

Out of Africa

For decades, palaeoanthropologists argued over the origins of our species.  Did Homo sapiens originate from Africa or did we evolve from hominins that had spread across Europe, the Middle East and Asia much earlier?  Whilst most scientist now agree that Africa was the “cradle of mankind”, skeletal remains from various locations and new research into ancient climates, particularly the prehistoric climate of the Arabian peninsula, hinted that modern humans may have migrated out of Africa earlier than 60,000 years ago.

Certainly, the migration of modern hominins (and we include Neanderthals and the enigmatic Denisovans within this group), seems to be much more complicated than previously thought.  Fluctuating global climates allowed a number of migrations to take place with different species of people occupying different areas and indeed mixing at various points in our short history.  Our family tree resembles a very gnarled and twisted sapling.

To read a related article that looks at how changing climates in the Arabian peninsula may have had an impact on human migration: Out of Africa and into Arabia.

Five Hundred Human Genomes Analysed (Almost)

Most non-Africans can trace their heritage back to a group of humans that left Africa around 60,000 years ago.  However, the study of almost five hundred human genomes (483 to be precise, from 148 world-wide populations), undertaken by scientists at the Estonian Biocentre has found traces of a much earlier “Out of Africa” human migration.

Faint traces of an earlier human migration were recorded in the DNA of the people of Papua New Guinea, but this study suggests that these earlier human pioneers all but vanished, so it does not alter drastically the prevailing theories as to the ancestors of the majority of us.  The researchers suggest that a genetic signature representing around 2% of the genome in present-day Papuans originates from an earlier and largely extinct expansion of anatomically modern humans out of Africa.

This data, together with fossil evidence and a recently published paper indicating a genetic mixing of Neanderthals and modern humans predating the main Eurasian expansion* contributes to the growing evidence to support the presence of our species outside Africa earlier than 75,000 years ago.

The paper published in the journal “Nature” and available as a pdf: “Genomic Analyses inform on Migration Events during the Peopling of Eurasia”.

Attempting to Map Human Migration out of Africa – When Did this Take Place?  How Many Times?

A model of modern human being (H. sapiens).

The figure in the picture is from the Bullyland model range.

To view the range: Bullyland Prehistoric Animal Figures.

Doctor Luca Pagani, lead author of the paper stated:

“All the other Eurasians we had were very homogenous in their split times from Africans.  This suggests most Eurasians diverged from Africans in a single event… about 75,000 years ago, while the [Papua New Guinea] split was more ancient, about 90,000 years ago.  So we thought there must be something going on.”

Same Edition of “Nature” Different Conclusions

In another paper, also published in “Nature” a team of scientists including researchers from the Estonian Biocentre (such as an author of the first paper – Mait Metspalu), as well as scientists from the Harvard Medical School and the New York Genome Centre, along with colleagues from a number of other institutions, came to a slightly different conclusion.

In this study, 300 genomes from 142 different populations were analysed and evidence was found of early splits in the populations within Africa, along with a single migration event that gave rise to non-African humans.

However, in this paper, no substantial evidence of an early (pre-60,000 years ago), African exodus was identified in the genomes of Papuans and other related populations such as of those groups that make up the Aboriginal race of Australia.  This team of scientists conclude that if, the genetic legacy of a more ancient migration survives in these populations, it cannot comprise more than a tiny portion of the entire genome.

The paper: “The Simons Genome Diversity Project: 300 Genomes from 142 Diverse Populations”.

A Third Study – Similar Conclusion

Papers on human ancestry must be a bit like buses.  You wait a while and nothing and then three come along at once.

In a third paper, also published in “Nature”, a study of the genomes of the Aboriginal race of Australia by researchers from the Centre for GeoGenetics, the Denmark Natural History Museum affiliated to the University of Copenhagen, along with colleagues from a number of other institutions including the Max Planck Institute, University College London and (once again), Mait Metspalu of the Estonian Biocentre, a similar conclusion to paper two is reached.  That, if there was an earlier human migration, then it is represented by only a tiny portion of the genome of living people from Oceania and Australia.

The title of this paper: “A Genomic History of Aboriginal Australia”.

Professor David Reich (Harvard Medical School) and a member of the Simons Genome Diversity Project that published the second paper summarised the research as follows:

“In our paper, we exclude more than about 2% ancestry in Australians, Papuans, and New Guineans from an early dispersal population, and our best estimate is 0%.  I am a bit concerned that poorly modelled features of the methods used by Pagani and colleagues [“Genomic Analyses inform on Migration Events during the Peopling of Eurasia”] may have contributed to a false-positive signal of early dispersal ancestry in them.  However, an alternative possibility is that the truth is around 2%, and this might just be consistent with all three studies.”

No Definitive Signature for an Earlier African Migration

Dr Mait Metspalu, the scientist who figured in all three publications stated that although the other papers do not detect a definitive signature for an earlier African migration by anatomically modern humans, this idea is not rejected, so long as it just contributes to a tiny portion of the genome in people alive today.

We leave it to the esteemed Professor Chris Stringer from the London Natural History Museum for the final word (for the moment), on this aspect of human ancestry.

Professor Stringer explained that the analysis undertaken by the Simons Genome Diversity Project and those scientists who studied the genome of the indigenous Australians favour the theory of a single migration event out of Africa less than 80,000 years ago giving rise to all living non-Africans.  In contrast, the paper with Doctor Luca Pagani as lead author, supports the idea of an additional and earlier modern human migration out of Africa more than 100,000 years ago, genetic traces of this earlier exodus can be found in Papuans, et al.

Tying It All in with the Human Fossil Record

There is certainly fossil evidence to indicate that our species (H. sapiens) was living outside Africa in the Near East, the Middle East and indeed elsewhere more than 60,000 years ago.  However, the paucity of the human fossil record, coupled with problems over dating bones and teeth in conjunction with a rather confusing picture involving interbreeding between several species of humans (Neanderthals, Denisovans and potentially yet another species of early human or two), has led to a rather muddled picture.

All three papers, although drawing slightly different conclusions, are helping to contribute to a greater understanding with regards to our own ancestry and we expect this lively debate to continue.  The evidence is likely to ebb and flow between the different scientific viewpoints, ironically, in a very similar pattern of backwards and forwards that most probably occurred with hominin species as they migrated in and out of various regions in response to climate change and other pressures.

Visit Everything Dinosaur’s website: Everything Dinosaur.

A view articulated in a letter entitled “Human migration: Climate and the Peopling of the World”, co-authored by Professor Chris Stringer and coincidently also published in the latest edition of “Nature”.

*For the related article published in February which suggests that modern humans and Neanderthals may have interbreed 100,000 years ago: Mapping the Ancient Gene Flow between Ourselves and Neanderthals.

Colour, Camouflage and Countershading in Dinosaurs

It turns out that the little dinosaur Psittacosaurus (parrot lizard), was light underneath and darker on its back.  This colour pattern, known as countershading is a common form of camouflage in extant animals.  Scientists including researchers from Bristol University conclude this in a new study of a beautifully preserved Psittacosaurus specimen currently on public display at the Senckenberg Museum of Natural History in Germany.  The study has been published in the academic journal “Current Biology”.

Calculating the Colour of Psittacosaurus

Reconstructing the Colour of Psittacosaurus

Physical reconstruction of Psittacosaurus with original colour patterns.

Picture credit: Jakob Vinther and Bob Nicholls

Knowing the potential colour of an animal gives clues to its probable habitat.  The research team postulate that this little herbivore lived in an environment with diffuse light, such as in a forest.  To test this idea, a three-dimensional model of this Early Cretaceous dinosaur was created, step forward the very talented Bob Nicholls who has made a number of prehistoric animal models before for various museums and exhibitions.

A Superb Fossil Specimen

The specimen on display at the Senckenberg Museum of Natural History, most likely originates from the Yixian Formation of Liaoning Province, China.  The fossil was illegally exported from China, in violation of Chinese law, but was purchased by the German museum.

The Fossilised Skeleton of Psittacosaurus (Senckenberg Museum of Natural History)

Psittacosaurus, early Cretaceous (120 million years old), preserving skin with colour patterns, Senckenberg Museum, Frankfurt, Germany.

Picture credit: Jakob Vinther and Robert Nicholls

Evidence of Countershading with Psittacosaurus

One of the authors of the new scientific paper, Dr Jakob Vinther (School of Earth Sciences and Biological Sciences, Bristol University) stated:

“The fossil, preserves clear countershading, which has been shown to function by counter-illuminating shadows on a body, thus making an animal appear optically flat to the eye of the beholder.”

Behavioural ecologist and co-author of the study, Professor Innes Cuthill from the School of Biological Sciences, added:

“By reconstructing a life-size 3D model, we were able to not only see how the patterns of shading changed over the body, but also that it matched the sort of camouflage which would work best in a forested environment.”

Countershading  most likely served to protect Psittacosaurus, a facultative biped and a member of the bird-hipped dinosaur group (ornithischians), against predators that use patterns of shadow on an object to determine shape, just as we humans do.

Dr Vinther realised that structures previously thought to be artefacts or dead bacteria in fossilised feathers were actually “melanosomes,” small structures that carry melanin pigments found in the feathers and skin of many animals.  In some well-preserved specimens, such as the Psittacosaurus the researchers worked on in the new study, it is possible to make out the patterns of preserved melanin without the aid of a microscope.

The Distribution of Countershading

Professor Cuthill and colleagues at Bristol had also been exploring the distribution of countershading in modern animals.  But it was no easy matter to apply the same principles to an extinct animal that had been crushed flat and fossilised.  To explore this idea further they teamed up with local palaeoartist, Bob Nicholls in order to reconstruct the remarkable fossil in to a physical model which, they say, is the most scientifically accurate life-size model of a dinosaur with its real colour patterns.

Days of careful studies of the fossil, taking measurements of the bones, studying the preserved scales and the pigment patterns, with input on muscle structure from Bristol palaeontologists Professor Emily Rayfield and Dr Stephan Lautenschlager, led to months of careful modelling of the dinosaur.
Bob Nicholls explained:

“Our Psittacosaurus was reconstructed from the inside-out.  There are thousands of scales, all different shapes and sizes, and many of them are only partially pigmented.  It was a painstaking process but we now have the best suggestion as to what this dinosaur really looked like.”

Investigating the Environment

In order to investigate what environment the psittacosaur had evolved to live in, Dr Vinther, Bob Nicholls and Professor Cuthill took another cast of the model and painted it all grey.  They then placed it in the Cretaceous plant section of Bristol Botanic Garden and photographed it under an open sky and underneath trees to see how the shadow was cast under those conditions.  By comparing the shadow to the pattern in the fossil they could then predict what environment the psittacosaur lived in.

Psittacosaurus in the Bristol Botanic Garden

Psittacosaurus photographed in the Bristol Botanic Garden.

Picture credit: Jakob Vinther

Living in a Forest Environment

Dr Vinther stated:

“We predicted that the psittacosaur must have lived in a forest.  This demonstrates that fossil colour patterns can provide not only a better picture of what extinct animals looked like, but they can also give new clues about extinct ecosystems and habitats.  We were amazed to see how well these colour patterns actually worked to camouflage this little dinosaur.”

Psittacosaurus, which Professor Cuthill describes as “both weird and cute, with horns on either side of its head and long bristles on its tail”, lived in the Early Cretaceous of China and has been found in the same rock strata where many feathered dinosaurs have been discovered.  A number of species have been assigned to the Psittacosaurus genus, more species assigned to this genus than in any other genus of the Dinosauria.

Congratulating the Researchers

Everything Dinosaur congratulates the researchers for this most insightful study and also acknowledges the efforts of the design team at the model maker CollectA for producing such an accurate representation of Psittacosaurus in the company’s dinosaur model range.

The Accurate CollectA Psittacosaurus Dinosaur Model

A typical psittacosaurid.

Picture credit: Everything Dinosaur

The picture (above) shows a model of Psittacosaurus (CollectA).

To view this model range: CollectA Prehistoric Life Models and Figures.

The deposits that make up the Yixian Formation include evidence for a forest environment (based on wood and plant fossils).  The researchers say that they would now like to explore other types of camouflage in fossils and to use this evidence in understanding how predators could perceive the environment and to understand their role in shaping evolution and biodiversity.

The Scientific Paper: Vinther, J., Nicholls, R., Lautenschlager, S., Pittman, M., Kaye, T. G., Rayfield, E., Mayr, G. and Cuthill, I. C. 2016. “3D Camouflage in an Ornithischian Dinosaur”. Current Biology.

Everything Dinosaur acknowledges the help of Bristol University in the compilation of this article.

Visit Everything Dinosaur: Everything Dinosaur.