CROCODILES WENT THROUGH A VEGETARIAN PHASE, TOO
Imagine you’re a small mammal of the Mesozoic. Snuffling around one day, you run into a cat-size, scaly, big-eyed reptile that looks not unlike a crocodile found later in the 21st century. Spotting you, he opens his mouth wide to reveal … tiny, intricate teeth. Then he turns his head and munches on some leaves.
Such encounters may have been common in prehistory. Research published in Current Biology suggests that vegetarianism evolved at least three separate times in ancient crocs — a conclusion reached after scientists studied the unusual teeth sported by many species, including the Simosuchus described above.
Today, crocodiles and their relatives, among them alligators, caimans and gharials, can be found across the Southern hemisphere. They have many things in common, including meat-heavy diets, a penchant for swimming and their teeth. Ask them to smile for a family reunion photo, and each mouth would bristle with simple, blunt-tipped cones.
But the Mesozoic was a different story. About 250 million years ago, scores of crocodyliform species could be found across the globe, some on land and some in seas and rivers. A particular species might eat only plants, only animals, or both. To support these varied diets, many had “unique, interesting teeth,” said Keegan Melstrom, a geobiology graduate student at the University of Utah and lead author of the new study.
Melstrom has been keen on crocodile teeth since 2011, when he saw a presentation on an extinct crocodyliform called Researchers believe ancestors of modern crocodiles evolved to survive on a plant diet at least three times. Pakasuchus. Pakasuchus had canines in the front of its mouth and molars in the back. When its jaw closed, the teeth would neatly slot together — more like a mammal’s mouth than the akimbo grin of modern crocodiles. “It just blew my mind,” Melstrom said.
For the new study, Melstrom and his co-author, Randall Irmis, analyzed 146 teeth from 16 extinct crocodyliform species. They used a method called orientation patch count rotated. From a scan of an object, the method generates a numerical score indicating the complexity of the object’s shape. “It allows us to compare teeth that have no landmarks in common,” said Melstrom.
This proved especially useful for studying prehistoric crocs, he said, whose teeth often have “no modern-day analogues.”
The researchers gathered the complexity scores of the teeth and compared them to those of living reptiles and mammals with known diets. Half of the ancient species seemed to have been on the plant-eating end of the spectrum — “a genuine surprise,” Melstrom said.