Some prehistoric crocs were vegetarians


The shape of their teeth tells a complex story. Dyani Lewis reports.


False colour 3D images showing the range in shape of crocodyliform teeth. Carnivores (left), such as the living Caiman, have simple teeth, whereas herbivores (right) have much more complex teeth.

Keegan Melstrom

Today’s crocodiles have some of the most gruesome table manners: drowning and then swallowing their prey whole or leaving a carcass to rot before thrashing around until bite-sized chunks of flesh break off.

But the prehistoric relatives of crocodiles and alligators – members of the group known as crocodyliforms – weren’t all fearsome carnivores.

A handful of species living during the age of the dinosaurs were even vegetarian, an analysis of fossil teeth has found. The findings are published in the journal Current Biology.

Keegan Melstrom and Randall Irmis from the University of Utah, US, carefully studied differences in the shape of 146 teeth from 16 different extinct crocodyliforms from the Mesozoic, a period that stretched from around 250 million years ago until the demise of the dinosaurs 66 million years ago.

They used a technique called OPCR (orientation patch count rotated), which quantifies the complexity of the tooth surface. In mammals, the method can predict which teeth match with meat-based or plant-based diets.

Melstrom and Irmis found the technique worked just as well on extinct reptile teeth.

"Carnivores possess simple teeth whereas herbivores have much more complex teeth," says Melstrom. "Omnivores, organisms that eat both plant and animal material, fall somewhere in between.”

The analysis found that extinct crocodyliforms were a mixed bag when it comes to diet. "Some were similar to living crocodylians and were primarily carnivorous, others were omnivores, and still others likely specialized in plants,” says Melstrom.

In the crocodyliform family tree, not all vegetarians clustered together on the same branch.

“Complex teeth, which we infer to indicate herbivory, appear in the extinct relatives of crocodiles at least three times and maybe as many as six in our dataset alone," says Melstrom.

This suggests that herbivory evolved independently multiple times, and in different locations around the world.

In some instances, herbivorous crocodyliforms would have lived alongside herbivorous mammals and their relatives.

Whether the two competed for the same foods or specialised in different plant species is unknown. But this sharing of an ecosystem’s plant resources by mammals and crocodyliforms isn’t something that happens in any modern ecosystem.

  1. https://www.cell.com/current-biology/fulltext/S0960-9822(19)30690-6
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