Carnivorous Croc Cousin Stalked the Triassic Carolinas

Movies have teasers. Books have sample chapters. And for fossils, there are photos of “unnamed taxa” in presentations and figures shared in hushed corner conversations.

At paleo conferences held over the past few years, I kept seeing glimpses of a strange fossil animal from North Carolina. All that surfaced were images a multi-pronged fossil with a mesh of bone in the center – part of an ancient reptile’s cheek – and the scuttlebutt had it that this was a big, bad carnivore. Today, in the pages of Scientific Reports, paleontologists Lindsay Zanno, Susan Drymala, Sterling Nesbitt, and Vincent Schneider throw back the curtain on the creature and confirm that the rumors were true.

Given that prehistoric predators require titles as impressive as their physical stature, the researchers have named their new animal Carnufex carolinensis – the “Carolina butcher”. It was the top-tier carnivore in the 231 million year old habitats of North Carolina, and was a part of the wider, ancient group that today’s alligators and crocodiles belong to, called the crocodylomorpha.

Exactly how imposing Carnufex would have been in life is difficult to say. So far, only parts of the skull, pieces of vertebrae, ribs, and a left humerus have been found. But Zanno, Drymala, and coauthors estimate that their Carnufex reached about 10 feet in length. That was large enough to make it among the largest carnivores in its habitat, and Carnufex likely reached even greater stature. The sutures between the predator’s skull bones weren’t fused when the animal died, the researchers note, meaning that this particular Carnufex was still growing when it started its 231 million year journey in the fossil record.

Carnufex and the crocodylomorphs weren’t the only big carnivores around during the Triassic, though. Zanno, Drymala, and colleagues point out that at least five different lineages of archosaurs – or “ruling reptiles” – included apex predators in their ranks. Most were what paleontologists call croc-line archosaurs – an array of animals on the branch only represented by alligators, crocodiles, and gharials today – but some early dinosaurs were large enough to compete with their distant croc cousins. In terms of numbers and top sizes, though, croc-line archosaurs were the real rulers of the Triassic.

A mass extinction changed the balance. Many lineages of croc-line archosaurs, including some that moved just like early dinosaurs, died out. Only the crocodylomorphs survived, and, even then, the large carnivores like Carnufex were gone. For reasons as-yet-unknown, early dinosaurs were virtually unaffected by the extinction, and, freed from competition, rapidly evolved into a startling array of new forms. Dinosaurs were only able to become truly “terrible lizards” once Carnufex and its kin stepped back from the evolutionary spotlight.

Reference:

Zanno, L., Drymala, S., Nesbitt, S., Schneider, V. 2015. Early crocodylomorph increases top tier predator diversity during rise of dinosaurs. Scientific Reports. doi: 10.1038/srep09276