What evolutionary pressures led to crocodyliforms having plant-dominated diets remains a mystery.

If a time machine that sent you back to the Mesozoic Era, not all the crocs you'd come across would size you up as a tasty meal.

That's according to a new study published in Cell Press on Thursday that fed high-res scans of 146 teeth from 16 extinct species into a computer model and determined that, unlike their modern progeny who renowned for their ferocity, some early crocodyliforms were an altogether more peaceful lot.

"What's really fascinating about this is a lot of these teeth are unlike anything we see today," Keegan Melstrom, a doctoral student at the University of Utah who conducted the research along with his supervisor Randall Irmis, told AFP.

To determine what tooth complexity reveals about diet, Melstrom relied on previous work on heterodonty in mammals, and his own earlier findings about teeth differences in reptiles.

"Some were similar to living crocodylians and were primarily carnivorous, others were omnivores, and still others likely specialized in plants," he said, adding that they lived on different continents and at different times.

While some of these species probably looked a lot like modern day alligators or crocodiles, others were smaller, lived entirely on land unlike their semiaquatic descendants, and had legs beneath their bodies.

"And I kind of think of these ones as a hairless, armored dog or cat," he told AFP.

What remains a mystery, however, is what evolutionary pressures led to crocodyliforms having plant-dominated diets, and why they disappeared.

Agence France-Presse