Before dinosaurs dominated the Earth, distant crocodile relatives lived on land and in water, though they were believed to live quite separate lives until a recent discovery.

Reported in a press release, a scientist at the University of Tennessee (UT) - Knoxville found a tooth in the thigh of one of those ancient reptiles may rewrite the book on how these creatures interacted. For their study, published in the German journal Naturwissenschaften, they examined a 220-million-year-old fossil containing telling bite marks.

The tooth they found belonged to the phytosaur, an ancient croc relative that dwelled in the water but could walk on land. The tooth was buried two inches into the thigh of a rauisuchid, a land-based reptile, though it had apparently survived the phytosaur attack with the bone lodged underneath its skin.

"To find a phytosaur tooth in the bone of a rauisuchid is very surprising. 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," Stephanie Drumheller, an earth and planetary sciences professor at UT - Knoxville, said in the release. "Finding teeth embedded directly in fossil bone is very, very rare.

"This is the first time it's been identified among phytosaurs, and it gives us a smoking gun for interpreting this set of bite marks."

Drumheller teamed up with Michelle Stocker and Sterling Nesbitt, both of Virginia Tech, to carefully examine the rare fossil. As not to destroy the bone with a tooth in it, they had to recreate it with 3-D printers. If not for the tooth, they may have never known who the rauisuchid's attacker was.

"This research will call for us to go back and look at some of the assumptions we've had in regard to the Late Triassic ecosystems," Stocker said in the release. "The aquatic and terrestrial distinctions made were oversimplified, and I think we've made a case that the two spheres were intimately connected."