This 'Predator Croc' Stalked the Earth 240 Million Years Ago

The period immediately before the era of the dinosaurs is a mystery to most people. The planet wasn't empty or sterile; it was full of animals large and small, both on land and in the seas.

Those animals aren't as well known as dinosaurs, but they're of great interest to paleontologists, including Sterling Nesbitt of Virginia Tech, who at only 32 years old has already named more than a half-dozen new species of prehistoric vertebrates. His newest discovery, detailed in the Journal of Vertebrate Paleontology, is named Nundasuchus ("NOON-dah-SOO-kuss"), a combination of Swahili and Greek words meaning "predator crocodile."

Nesbitt first found pieces of Nundasuchus bones back in 2007, and ever since has been making trips back and forth and piecing all these bones together, like an incredibly complex, ancient jigsaw puzzle. Now he finally has a good idea of what the entire creature looked like, so he's given it a name and published a paper about it.

Nundasuchus is one piece of the confounding puzzle of the archosaurs, a huge group of both extinct and still-living animals that include the modern crocodilians (crocs, alligators), all birds, dinosaurs, and flying reptiles like pterosaurs.

"It's a little weird to think about, but crocodiles and birds are each others' closest living relatives, today," says Nesbitt. "And they shared a common ancestor that lived about 250 million years ago."

He describes the broad structure of this family tree as an old slingshot, with lots of little splinters peeling off. One arm of the slingshot is the dinosaurs, and a splinter on that arm is the birds. The other arm is the crocodilians. Finding the very nook of the slingshot, where the two arms meet the handle, is a continuous quest, because that nook has the common ancestor of both of these huge, variable groups of animals. Nundasuchus probably isn't that common ancestor, but it's awfully close to that nook.

Nesbitt traveled to Tanzania specifically looking for something like Nundasuchus. He was trying to find animals that date from around 250 million years ago, when an event called the Permian-Triassic Extinction Event (commonly known as the Great Dying) occurred. The Great Dying is the biggest known extinction event in the planet's history, bigger than the event which killed all the last of the dinosaurs; up to 96 percent of all marine life and around 70 percent of all land vertebrates became extinct. Figuring out what was living just before the Great Dying can inform how we understand the development of what came after. The few species that survived were the ones that would dominate the planet in the coming era of the dinosaurs.

The specimen of Nundasuchus that Nesbitt discovered in Tanzania is about nine feet long, shaped sort of like a cross between a modern crocodile and a dinosaur. It was long, walked on all fours, and had bony plates on its back, but its legs were directly under its body, more like a dinosaur (or a mammal!) than a modern-day reptile. Its teeth are a major clue as to what the animal's life was like. "We know their teeth kinda looked like steak knives, so they're eating meat," says Nesbitt. "If they're not the top [predators], they're pretty close to the top." And this specimen wasn't even full-grown. Paleontologists can tell a very rough age of an animal by looking at how far along its bones are in processes like ossification (the actual forming of bones). This Nundasuchus wasn't fully grown; Nesbitt says a mature adult could have been more like 15 or 20 feet long.

The world it lived in was pretty different from the era following the Great Dying, or the modern age. "There was no grass, and there were no flowering plants at the time, which is pretty weird to think about," says Nesbitt. "There'd be more like pine forests, with ferns everywhere." The animals, too, were different; there were some, like Lystrosaurus, which were more like mammals than the reptiles we're now familiar with. Lystrosaurus, the most common animal of its time, may have even had fur. But, says Nesbitt, "it was really the time of the crocodile relatives." During Nundasuchus's era, dinosaurs would have been small, maybe even prey animals for Nundasuchus.

Nundasuchus didn't evolve into today's crocodilians; it is its own little splinter peeling off of that slingshot. (You can think of it this way: we didn't evolve from chimps, but both we and chimps evolved from some common ancestor. Alligators and Nundasuchus are more like cousins than anything else.) The animals from the that survived the Great Dying were one specific lineage of crocodilians (from which eventually came the modern crocodilians), some flying reptiles, and some dinosaurs. "That's why Nundasuchus is so important; it's something that's never been found before," says Nesbitt. "It represents that early form of an archosaur, it has that body type." Nundasuchus was present at a key time in the development of incredibly important and fascinating animals; it was there right when the archosaurs began to diversify.

It's a huge, important find, and Nesbitt, like a lot of paleontologists, still has that kind of childlike amazement at finding a creature that walked the same earth he walks, hundreds of millions of years ago. "It's kind of incredible if you think about it, because that animal died 240, 245 million years ago. And even though it died, it had to be buried," he says. "And those rocks had to be buried deeply, and not weathered, and then brought up to this tiny tiny slice that we live in today, and one of us had to find it before all of those bones washed away." We may not know much about that important era when dinosaurs, crocodilians, and other reptiles collided just before nearly every animal on the planet perished, but this is a major step forward to figuring out just what was going on then.​