This American alligator, like crocodiles and other related species, is a meat-eating power biter. (Credit: U.S. Fish & Wildlife Service)

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Someone says “crocodiles” and the image that comes to mind is probably a toothy one. Modern crocodilians are power biters, and many species are apex predators. But it wasn’t always that way.

Paleontologists believe that multiple extinct species preferred plants over prey.

Toothfully Speaking

Humans, like most mammals, are heterodonts: We have different kinds of teeth specialized for various tasks. Just sweep your tongue around your mouth and you’ll feel the pointy canines, chisel-like incisors and large, grinding molars and premolars.

Our diverse dentition is one reason we’re such efficient omnivores. We’ve got a tooth for every task, whether it’s biting off a piece of beef jerky or grinding corn into a swallow-friendly slurry.

Today’s crocodilians — crocodiles, alligators, caimans and gharials — have much less diversity in their mouths. While there is some variation in size and shape, crocodilian teeth are basically elongated cones, perfect for grabbing, nabbing and stabbing prey.

The predecessors of crocodilians, however, the crocodyliforms, had some serious heterodonty happening. Teeth from several species, such as the cat-like Pakasuchus, show an almost mammal-like degree of tooth variation and complexity.

Artist renderings of extinct crocodyliforms reveal a large degree of heterodonty, or different shapes and sizes of teeth, typically related to differences in diets. (Credit: Jorge Gonzalez)

To Crunch Or Not To Crunch

Researchers analyzed nearly 150 teeth from numerous crocodyliform species, comparing their complexity with those of other reptiles and mammals. They found that, while some of the species analyzed appeared to be dedicated meat-eaters, others showed clear signs of herbivory, or plant-eating.

Going vegan typically means having teeth that can grind plant matter into digestible pieces, which requires a fairly complex tooth shape. Three of the crocodyliform species analyzed in the research had greater tooth complexity than any living reptile.

Of the crocs studied, smaller-bodied species were more likely than the big ‘uns to have complex dentition. It suggests the biggest of the crocodyliforms were steadfast carnivores.

The researchers concluded that herbivory occurred in the crocodyliform lineage at least three times during the Mesozoic, about 66 million-201 million years ago.

The Mesozoic is better known as the Age of Dinosaurs, but, in this case, it’s mammals that make things interesting. Or at least Mesozoic mammaliamorphs, the predecessors to mammals.

The authors behind today’s study note that, according to the fossil record, herbivorous mammaliamorphs and herbivorous crocodyliforms of similar size overlapped at several times. That means you had plant-eaters from two very different lineages peacefully noshing in the same ecological niche.

It’s a phenomenon not seen in today’s ecosystems, where modern crocodilians find mammals delicious.

The study appears today in Current Biology.