US - In children’s books and cartoons, crocodiles and their kin tend to have an impressive array of identical teeth, each shaped like a sharp, pointed weapon primed for tearing through flesh. In reality, there is often a bit more variation, says paleontologist Keegan Melstrom of the University of Utah.

“But that is nothing compared to the staggering diversity in the teeth of extinct crocodile-like reptiles, or Crocodyliformes,” he says. “Some of those extinct crocs had really weird teeth.”

The adaptive American crocodile thrives on land and in water, using a nictitating membrane to see underwater.

Now, an analysis of 146 fossilized teeth belonging to 16 extinct crocodile relatives has revealed something surprising: At least three times in their history, ancient croc cousins became vegetarians.

“This shows that this was a succesful dietary strategy,” says Melstrom, whose team presents the results today in the journal Current Biology. “And I think that as we find more teeth in the future, we are likely to find even more groups that independently became herbivores.”

Dedicated chomping

For their analysis, Melstrom and coauthor Randall Irmis, also of the University of Utah, adopted a method that was especially developed to compare dissimilar teeth, borrowed from earlier work by paleontologists studying ancient mammals.

“What it comes down to is that we count how many separate surface areas there are on every tooth,” Melstrom says. “We consider them to be separate if they are tilted in a different direction.”