Giant reptiles of the land once fought with giant reptiles of the sea. The truth is in a single tooth, preserved in a fossilized bone.

210 million years ago, phytosaurs and rauisuchids were the two most dominant predatory species on Earth. Scientists used to think that phytosaurs and rauisuchids had little interaction, because phytosaurs lived in the sea and rauisuchids lived on the land. However, new fossil evidence shows that the two species may have not only interacted with each other, but actually sought out encounters. Researchers found a fossil of the thigh bone of a rauisuchid with the tooth of a phytosaur inside.

This incredible find sheds some light on the way early creatures interacted with each other around the time when Pangea was just beginning to break apart.

"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," said Stephanie Drumheller, one of the paleontologists who made this discovery and wrote the research paper about the find.

The tooth was discovered by chance at the University of California Museum of Paleontology in Berkeley. It had healed over by bone, which means that the rauisuchid survived being bitten.

"It was remarkable we were able to reconstruct a part of an ancient food web from over 210 million years ago from a few shallow marks and a tooth in a bone. It goes to show how careful observation can lead to important discoveries even when you're not seeking those answers," said Sterling Nesbitt, one of the co-authors of the paper.

The paper was published online this month in the German journal Naturwissenschaften.

Rauisuchids were huge, running up to 20 feet tall, with heads as long as two feet. Phytosaurs were very large as well, up to 40 feet long, bearing a remarkable similarity to today's crocodiles (although much larger than modern crocs).

This new find could have huge implications for what we know about the Late Triassic food chains, according to Michelle R. Stocker, another co-author of the paper. She added that the animals that lived in the land were probably intimately connected to animals that lived in the sea at the time, and said that scientists may need to re-think the distinctions they once made between those two groups. This could be a huge starting point for research on the subject.