Scientists have long believed that the dinosaurs that lived on land and those that thrived in the water did not interact much with each other. However, an analysis of prehistoric bite marks and tooth that University of Tennessee (UT) researchers found in the thigh of one of these animals could change scientists' views on how ancient reptiles interact with each other when they emerged on Earth during the Triassic period.

Stephanie Drumheller, from UT's Department of Earth and Planetary Sciences, and colleagues found a tooth of a phytosaur, a crocodile-like predator that thrived in rivers and lakes during the Late Triassic period, lodged in the thigh bone of the rauisuchid, a large terrestrial predator.

More than 200 million years ago, these two animals were both apex predators, which mean that each was the top predator in their food chain. The tooth and bite marks provide evidence that aquatic and terrestrial dinosaurs interacted and even engaged in savage fights millions of years ago.

The phytosaur's broken tooth was buried two inches deep into the rauisuchid's bone and then healed over suggesting that the terrestrial giant survived the semi-aquatic dinosaur's initial attack.

"The larger femur preserves a rare history of interactions with multiple actors prior to and after death of this ∼8-9-m individual," Drumheller and colleauges wrote in their study, which was published in the German journal Naturwissenschaften on Sept. 17. "A large embedded tooth crown and punctures, all of which display reaction tissue formed through healing, record evidence of a failed attack on this individual."

By using computed tomographic (CT) data, images of the tooth, 3D printer and through examination of the bite marks, the researchers also found evidence that the 25-foot-long rauisuchid was attacked twice and managed to survive. The analysis also gave clues as to which animal initiated the attack.

The researchers estimate that the phytosaur that attacked the rauisuchids, which were among the largest predatory dinosaurs in their environment at the time, was smaller than the rauisuchid and this indicate that size isn't enough to intimidate smaller carnivores from targeting and eating other predatory animals .

"These rauisuchids were the largest predators in their environments. You might expect them to be the top predators as well, but here we have evidence of phytosaurs, who were smaller, semi-aquatic animals, potentially targeting and eating these big carnivores," said Drumheller. "Thus, size cannot be the only factor in determining who is at the top of the food chain."

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