If you’re anything like me, I used to think that dinosaurs were dinosaurs and crocodiles were crocodiles. Easy to tell apart, right? Of course. Because crocodiles were sprawling quadrupedal semi-aquatic reptiles and dinosaurs were, ya know, dinosaurs.
But apparently over the last several decades it’s become more and more challenging for paleontologists to discern ancient croc fossils from dinosaurs, especially when dealing with crocodylomorph specimens that walked on two feet and were eerily similar to the theropods we’re familiar with, like Tyrannosaurus rex and Deinonychus (falsely named “velociraptor” in the movie, Jurassic Park, and which we also now realize had feathers).
I’ve been reading an excellent book called My Beloved Brontosaurus by Brian Switek, the science writer/paleontologist, and have learned so much more information about ancient crocs than I ever knew existed. For instance, in the Late Triassic period, dinosaurs were in their early days and not likely top of the food chain, especially within the regions we now know as North America. Instead, numerous varieties of quadrupedal and bipedal crocodylomorphs existed, whilst smaller dinos, similar to the early mammals, probably did their best to just avoid being eaten. It wasn’t until the End-Triassic Extinction that the sun set on the crocodilian heyday, wiping out much of the species variety, and dinosaurs stepped in to fill their places, leading to intense dinosaurian diversity in North America during the Jurassic and Cretaceous periods. (Mammals, meanwhile, continued to stay in the background and tried not to get eaten.)
According to Switek, strangely enough one of the most reliable ways to tell a bipedal croc fossil skeleton from a bipedal dino skeleton is the presence of a calcaneal tuber, aka a “heel”, similar to the heels of our own feet. While crocs have a heel, dinosaurs don’t and instead have a simpler hinge-like structure.
Note the heel of this bipedal crocodylomorph, Poposaurus.
Recently, researchers out of North Carolina State University and the NC Museum of Natural Sciences have reported findings of an early bipedal crocodylomorph, a species fondly named the Carolina Butcher, aka Carnufex carolinensis. It’s one of the earliest of the ancient crocs to have been discovered so far and helps scientists to better understand the early evolutions of both crocodylomorphs and dinosaurs in the Late Triassic period in North America. The team was able to image the skull with a surface scanner, shown below.
Given the Butcher’s size at over 3 meters, the new study adds further evidence to suggest that, while dinos may have been successful as competing predators in the southern hemisphere, in North America crocs ruled the land. So the next time you see a crocodile or alligator at the zoo, remember their two-legged ancient predator cousins and all the varieties of croc that this old earth has seen come and go. Perhaps it may put that sun-bathing crocodilian in a new light.