Meet the Carolina Butcher - the crocodile ancestor that walked on two legs and ruled the Earth

The Carolina Butcher - stomping all over the Earth 231 million years ago. Photo / Supplied

A terrifying crocodile which walked on its hind legs may have been the most deadly creature on Earth before the evolution of the biggest dinosaurs.

The newly discovered Carnufex carolinensis, or "Carolina Butcher," was a 9-foot long, land-dwelling proto-crocodile with huge snapping jaws.

It preyed on early mammals and armoured reptiles in the Late Triassic period, around 231 million years ago, when the Earth had just one huge continent, Pangea.

Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences, discovered parts of the Carolina Butcher's skull, spine and upper forelimb in Chatham County, North Carolina.

"The discovery of Carnufex, one of the world's earliest and largest crocodylomorphs, adds new information to the push and pull of top terrestrial predators across Pangea," said Dr Lindsay Zanno, assistant research professor at North Carolina State University.

"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."

Paleontologists knew that ancient crocodiles hunted alongside theropod dinosaurs but the new discovery suggests that they may have been top of the food chain.

"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," said Dr Zanno.

However as the Triassic drew to a close, extinction decimated both early dinosaurs and ancient crocodiles with only small-bodied crocodylomorphs and theropods surviving.

"Theropods were ready understudies for vacant top predator niches when large-bodied crocs and their relatives bowed out," added Dr Zanno. "Predatory dinosaurs went on to fill these roles exclusively for the next 135 million years."

The ancestors of modern crocodiles then took on a role similar to foxes or jackals, with small, sleek bodies and long limbs.

"If you want to picture these animals, just think of a modern day fox, but with alligator skin instead of fur," said Susan Drymala, graduate student at NC State and co-author of the paper.

Because the skull of the Carolina Butcher was in pieces, it was difficult to visualize what the complete skull would have looked like in life.

So to get a fuller picture the researchers scanned the individual bones with the latest imaging technology - a high-resolution surface scanner.

Then they created a three-dimensional model of the reconstructed skull, using the more complete skulls of close relatives to fill in the missing pieces.

The discovery was published in the journal Scientific Reports.