Ancient Crocs

Part of the Crocs: Ancient Predators in a Modern World exhibition. 

All in the Family

Crocodiles are part of a group of animals known as archosaurs, or “ruling reptiles." This group dominated land, sea, and sky across the planet for more than 150 million years. While they may look like lizards, crocs are more closely related to dinosaurs, including modern birds.

Prehistoric Body Plans

The only known fossil of the tiny crocodylomorph Hoplosuchus kayi.
© Carnegie Museum of Natural History

Crocs today are mostly aquatic animals, but many early crocodylomorphs—the group that includes living crocs and their extinct relatives—were small animals that lived on land. Hoplosuchus kayi was a tiny, graceful crocodile that lived about 140 million years ago in what is now Utah. With needle-like teeth and long legs built for running, it probably ate insects and other small animals. 

A Croc For All Seasons

Artist’s rendering of the pug-nosed crocodylomorph Simosuchus clarki.
Image courtesy of Wikimedia Commons

Hoplosuchus wasn’t the only animal that would be hard to recognize as a crocodilian. In their heyday, crocodylomorphs filled a huge variety of ecological roles, or niches. Metriorhynchids were dolphin-like crocodiles—lithe, unarmored aquatic hunters. Simosuchus, on the other hand, was a pug-nosed croc from Madagascar that lived on land, protected itself with thick, armadillo-like armor plates, and probably ate mostly plants.

Dinosaur Hunters

A fossil specimen of the ancient giant crocodile Deinosuchus hatcheri on display at the Natural History Museum of Utah. 
Image: Wikimedia Commons

Crocodiles as long as school busses and as heavy as elephants roamed the Earth as recently as 8 million years ago. These massive crocs tackled some of the most ferocious prey around: dinosaurs. Bite marks on the bones of two tyrannosaurs found in North America match the teeth of the giant crocodile Deinosuchus. One of the wounds was partially healed, signaling that these crocs weren’t just scavenging—they were hunting live tyrannosaurs. 

Lead image: Metriornychus jaekeli was an ancient marine crocodyliform with a body plan similar to modern dolphins. (Image courtesy of Wikimedia Commons)