Ancient crocodiles were plant-eaters according to study of their teeth

Ancient crocodiles, the distant cousins of modern crocodiles, were vegetarians according to a study done by scientists who studied their teeth.

Based on careful study of fossilized teeth, scientists Keegan Melstom and Randall Irmis at the Natural History Museum of Utah at the University of Utah have found that multiple ancient groups of crocodyliforms—the group including living and extinct relatives of crocodiles and alligators—were not the carnivores we know today, as reported in the journal Current Biology on June 27, 2019. In fact, the evidence suggests that a veggie diet arose in the distant cousins of modern crocodylians at least three times.

“The most interesting thing we discovered was how frequently it seems extinct crocodyliforms ate plants,” said Melstrom, a doctoral student at the University of Utah. “Our study indicates that complexly shaped teeth, which we infer to indicate herbivory, appear in the extinct relatives of crocodiles at least three times and maybe as many as six.”

All living crocodylians possess a similar general body shape and ecology to match their lifestyle as semiaquatic generalist carnivores, which includes relatively simple, conical teeth. It was clear from the start of the study that extinct species showed a different pattern, including species with many specializations not seen today. One such specialization is a feature known as heterodonty: Regionalized differences in tooth size or shape.

Typically, carnivores have simple, conical teeth, while herbivores have more complex ones. The teeth of omnivores, or the creatures that eat both meat and plants, fall somewhere in between. When it comes to crocodiles, people often think of the apex carnivorous predators that they are today, with their sharp teeth that can easily cut through flesh.

In the study, researchers looked at 146 teeth from 16 extinct crocodyliforms. From the beginning, researchers already noticed the differences in the pattern of the teeth of the extinct species, and they were able to determine the diets of the creatures based on quantitative dental measurement as well as other morphological features.

Interestingly, the researchers found that while some of the species were carnivorous just like modern day crocodiles, some had varied omnivorous diets, while others even had herbivorous diets. Those with the carnivorous diets had pointed teeth for killing and eating their prey, but those with herbivorous diets had broader and bumpier teeth that were perfect for grinding leaves and plants. Based on their analysis, herbivorous diets actually arose in some of the extinct species at least three times and up to six times in the Mesozoic crocodyliforms.

“The herbivores lived on different continents at different times, some alongside mammals and mammal relatives, and others did not. This suggests that an herbivorous crocodyliform was successful in a variety of environments!” said lead researcher Keegan Melstrom.

The studywas published in Current Biology.

Plant eaters have more complicated teeth because plant material is often harder to digest than meat, he said.

“So the more you can break down plant material prior to a chemical digestion, the more nutrients you can suck out of that food.”

The team found examples of crocs that were probably herbivores all over the world — in China, Tanzania, Madagascar, North America and Europe.

Figure: Jorge Gonzalez

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