Researchers Discover Enormous Ancient Crocodile That Walked Upright

This is a life reconstruction of Carnufex carolinensis / Jorge Gonzales
Janet Fang 20 Mar 2015, 18:14

Before dinosaurs arrived to rule North America, one of the world’s earliest and largest crocodilian ancestors was the continent’s top predator. The newly discovered 231-million-year-old fossil would have been about three meters (nine feet) long when it was alive. It lived on land, walked upright, and sliced through armored reptiles and early mammal relatives with its bladelike teeth. In a study published in Scientific Reports this week, researchers named it Carnufex carolinensis, or the Carolina butcher. 

The butcher’s partial skull, jawbone, some teeth, ribs, vertebrae, and a forelimb were unearthed in Late Triassic sediments of the Carnian Pekin Formation in what’s now Chatham County, North Carolina. Because the skull was preserved in pieces, North Carolina State University’s Lindsay Zanno and colleagues scanned the individual bones using a high-resolution surface scanner to create a 3D reconstruction. 

Here’s the reconstructed skull. The 3D surface models of skull bones are shown in white, and the gray areas are missing elements reconstructed from close relatives:

During the Late Triassic, North Carolina was a warm, wet region near the equator that was just starting to break apart from the supercontinent Pangea. "Fossils from this time period are extremely important to scientists because they record the earliest appearance of crocodylomorphs and theropod dinosaurs, two groups that first evolved in the Triassic period, yet managed to survive to the present day in the form of crocodiles and birds," Zanno explains in a news release

Ancient crocodile relatives like the large-bodied rauisuchids and poposauroids also roamed Pangea. In what became the Southern Hemisphere, these carnivores hunted alongside the earliest theropod dinosaurs, “creating a predator pile-up," Zanno says. “Until we deciphered the story behind Carnufex, it wasn't clear that early crocodile ancestors were among those vying for top predator roles prior to the reign of dinosaurs in North America."

But their spot at the top didn’t last. A mass extinction event at the end of the Triassic about 200 million years ago wiped them all out, and only small-bodied crocodylomorphs and theropod dinos survived. "Theropods were ready understudies for vacant top predator niches when large-bodied crocs and their relatives bowed out," Zanno adds. "Predatory dinosaurs went on to fill these roles exclusively for the next 135 million years."

Meanwhile, the ancestors of our crocs today started to slim down: With their sleek bodies and long limbs, they took on the role of modern foxes and jackals. As study co-author Susan Drymala of NC State explains: "If you want to picture these animals, just think of a modern day fox, but with alligator skin instead of fur.”

Images: Jorge Gonzales (top), Lindsay Zanno (middle)

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