The Triassic Dome-Headed Archosaur

A new paper was published online this week on an archosaur with a fascinating head. The living archosaurs are crocodylians and birds, but the group includes many extinct animals like all the non-avian dinosaurs, pterosaurs, rauisuchians, aetosaurs, and more. All of the animals in this group have teeth in sockets and a couple of additional openings in the skull.

This new archosaur, Triopticus primus, is interesting because it has a dome-shaped head, similar to Pachycephalosaurusand its relatives, the dome-headed dinosaurs. This archosaur comes from the Otis Chalk Formation of the Triassic Period. That’s where the story becomes especially interesting.

The Otis Chalk Formation represents a time when archosaurs were evolving very different body shapes. These forms included toothless species, fast predators, armored herbivores, and long-snouted carnivores. Millions of years later, during the Jurassic and Cretaceous, when crocodylian relatives and dinosaurs had become dominant, many of these same body shapes evolved again. This represents major convergent evolution between early archosaurs and their later crocodylian and dinosaurian descendants.

Convergent evolution occurs when different groups independently evolve similar features. The wings of bats, birds, and pterosaurs are classic examples. These Triassic archosaurs evolved a wide diversity of body shapes, and it is notable that many of these forms reappeared later in evolutionary history.