Researchers have found the tooth of a 220-million-year-old semi-aquatic phytosaur embedded in the thigh bone of a terrestrial rauisuchid.

Both are giant prehistoric replies related to the modern crocodile, according to University of Tennessee at Knoxville press release.

The two animals were not previously believed to have interacted, as the rauisuchid is a land reptile and the phytosaur lived in the water. Both are from the Late Triassic period.

Researchers found that the tooth had snapped off and became buried two inches into the bone, with the wound healing over the top, which could mean that the rauisuchid had survived the initial attack.

"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," said lead researcher Stephanie Drumheller, according to the release.

The tooth was examined by using computer tomographic data (computer processed x-rays that create sectioned images) and printed 3D copies of the tooth, to make sure that the bone wasn't destroyed.

Bite marks were also examined, which helped them uncover a history of multiple encounters.

Evidence suggested that the rauisuchid survived two attacks, but was later defeated during another battle.

"Finding teeth embedded directly in fossil bone is very, very rare," said Drumheller. "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."

The research is challenging the theory that land and water-based food chains of the Late Triassic period were separate.

"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," researcher Michelle Stocker said, according to 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."

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