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Petrified teeth suggest that some ancient crocodiles were vegetarians



Two old herbivorous crocodiles, Chimaerasuchus (left) and Pakasuchus (right).
Image: Jorge Gonzalez / Gizmodo [1
965965] Crocodiles are among the scariest carnivores on earth today, but recent research suggests that their ancient relatives have developed a taste for plants.

A common misconception about crocodiles is that they have remained largely unchanged throughout their 200-million-year history. New research published in Current Biology provides further evidence that ancient crocodile forms – a group from which modern reptiles such as crocodiles, alligators, caimans, and gharials descend – have been more diverse in their evolutionary history than is normally assumed.

This study by the Natural History Museum of Utah suggests that some types of ancient crocodile forms are suitable for both herbivores and herbivores. The authors of the new paper, PhD student Keegan Melstrom and museum director Randall Irmis, arrived at this conclusion after careful analysis of fossilized crocodile-shaped teeth.

Today's crocodiles have rather boring teeth, both in terms of their complexity and the variability between the species. These living reptiles all have sharp, cone-shaped teeth – exactly the configuration you expect from ambushes in the water. These teeth are well-suited to grab wriggling prey and tear out pieces of meat.

False-color 3D images showing the shape of crocodile-shaped teeth.
Image: Keegan Melstrom

But when Melstrom and Irmis discovered, old crocodiles had teeth with a surprising degree of variability. In total, the team studied 146 fossil teeth from 16 different extinct species. Using high-resolution 3D mappings and casts of teeth collected from various institutes and researchers, they documented teeth that are as similar as they are today, as well as the milling of molars and canines reminiscent of modern mammals.

Some teeth, however, have been scratched on the head.

"We see all of these tooth forms in the history of reptile development, and some of them are fairly simple, but others simply have no comparison," Irmis said in a NHMU press release.

To further analyze the teeth, scientists used a method that allowed them to assess the physical complexity of each tooth. The technique took into account every nook and cranny and evaluated the tooth for its degree of complexity. "The more complicated the teeth are, the more plant material the animal eats," says Melstrom. At the same time, the teeth of omnivores "fall somewhere in between" in terms of physical complexity, he said.

Armadillosuchus, an extinct omnivore crocodile form.
Image: Keegan Melstrom

This analysis showed that some ancient crocodile forms that lived alongside dinosaurs were certainly malicious predators, but some omnivores added plants and insects to their diet. The extinct crocodyliform Armadillosuchus is one such example. And some might have unexpectedly been vegetarian only. Examples of these herbivorous crocodiles were Chimaerasuchus and Pakasuchus .

Intriguingly, the data suggested that this change in diet occurred independently of each other on three different evolutionary occasions, possibly even six. Herbivorous crocodiles appeared almost immediately after the mass extinction of the end triad and, according to the new findings, continued until the mass extinction of the end chalk. This is a distance of 135 million years, which was completed 200 to 65 million years ago. This new study shows the remarkable diversity of ancient crocodile forms and their mixed role in ancient food webs.

"Our work shows that extinct crocodile forms had an incredibly varied diet," Melstrom said. "The herbivores lived at different times on different continents, some not mammals and mammal mates, others not. This suggests that a herbivorous crocodile form has been successful in a variety of environments! "

Flanders University paleontologist Paul Willis told ABC News that the" true triumph "of the new paper was how Melstrom and Irmis could link functions to different teeth. These researchers were able to "nail the function of the teeth as an adaptation to plant, insect or omnivore," said Willis, who was not involved in the new work. "This is the breakthrough."

Looking to the future, the researchers hope to better understand how an environment pushes a species into a plant-based diet and why crocodiles are so strong after the extinction of the Triassic, but not after the Cretaceous alternate mass extinction.


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