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Repeated Evolution of Herbivorous Crocodyliforms during the Age of Dinosaurs
Some extinct crocs were vegetarians

by University of Utah

[Image: 1-someextinctc.jpg]
Life reconstructions of extinct crocodyliforms. Differences in tooth shape are related to differences in diets. Credit: Jorge Gonzalez

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. 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 Keegan 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.
"Carnivores possess simple teeth whereas herbivores have much more complex teeth," Melstrom explained. "Omnivores, organisms that eat both plant and animal material, fall somewhere in between. Part of my earlier research showed that this pattern holds in living reptiles that have teeth, such as crocodylians and lizards. So these results told us that the basic pattern between diet and teeth is found in both mammals and reptiles, despite very different tooth shapes, and is applicable to extinct reptiles."
To infer what those extinct crocodyliforms most likely ate, Melstrom and his graduate advisor, chief curator Randall Irmis, compared the tooth complexity of extinct crocodyliforms to those of living animals using a method originally developed for use in living mammals. Overall, they measured 146 teeth from 16 different species of extinct crocodyliforms.
Using a combination of quantitative dental measurements and other morphological features, the researchers reconstructed the diets of those extinct crocodyliforms. The results show that those animals had a wider range of dental complexities and presumed dietary ecologies than had been appreciated previously.

[Image: someextinctc.jpg]
False color 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. Credit: Keegan Melstrom/NHMU

Plant-eating crocodyliforms appeared early in the evolutionary history of the group, the researchers conclude, shortly after the end-Triassic mass extinction, and persisted until the end-Cretaceous mass extinction that killed off all dinosaurs except birds. Their analysis suggests that herbivory arose independently a minimum of three times, and possibly six times, in Mesozoic crocodyliforms.
"Our work demonstrates that extinct crocodyliforms had an incredibly varied diet," Melstrom said. "Some were similar to living crocodylians and were primarily carnivorous, others were omnivores and still others likely specialized in plants. 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!"
Melstrom says they are continuing to reconstruct the diets of extinct crocodyliforms, including in fossilized species that are missing teeth. He also wants to understand why the extinct relatives of crocodiles diversified so radically after one mass extinction but not another, and whether dietary ecology could have played a role.

Journal Reference:
Current Biology, Melstrom and Irmis: "Repeated Evolution of Herbivorous Crocodyliforms during the Age of Dinosaurs" , DOI: 10.1016/j.cub.2019.05.076

Extinct crocodyliforms from the age of dinosaurs (Mesozoic Era) display an impressive range of skeletal morphologies, suggesting a diversity of ecological roles not found in living representatives. In particular, unusual dental morphologies develop repeatedly through the evolutionary history of this group. Recent descriptions of fossil crocodyliforms and their unusual teeth provide the inferential basis for a wide range of feeding ecologies. However, tests of these hypotheses are hindered by the lack of directly comparable dental morphologies in living reptiles and mammals, thereby preventing an accurate ecosystem reconstruction. Here, we demonstrate, using a combination of the orientation patch count rotated method and discrete morphological features, that Mesozoic crocodyliforms exploited a much greater range of feeding ecologies than their extant relatives, including likely omnivores and herbivores. These results also indicate that crocodyliforms independently developed high-complexity dentitions a minimum of three times. Some taxa possess teeth that surpass the complexities of living herbivorous lizards and rival those of omnivorous and herbivorous mammals. This study indicates that herbivorous crocodyliforms were more common than previously thought and were present throughout the Mesozoic and on most continents. The occurrence of multiple origins of complex dentitions throughout Crocodyliformes indicates that herbivory was a beneficial dietary strategy and not a unique occurrence. Many of these crocodyliforms lived alongside omnivorous or herbivorous synapsids, illustrating an ecological partition that is not observed today.
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[-] The following 6 users Like Taipan's post:
  • Ausar, Claudiu Constantin Nicolaescu, Cryolophosaurus, Lightning, OldGreenVulture, Verdugo
Interesting. Its nice to know there are members of the croc family that are herbivorous.
It is indeed interesting.
So the aetosaurs were not the last vegetarian cousins of crocs.
[Image: 1200px-Cryolophosaurus_skeleton_mount_FMNH.jpg]

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