Dinosaurs Copied Triassic Reptiles

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.

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

Convergent evolution in Archosaurs.

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.  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 Triopticus primus.

The skull of the bizarre Late Triassic reptile Triopticus.

Picture Credit: Virginia Tech College of Science

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”

CollectA Pachycephalosaurus model.

A lithe Pachycephalosaurus dinosaur model.

Picture Credit: Everything Dinosaur

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