A tooth found embedded in a fossil leg bone is evidence of an unlikely battle between two top predators in the American Southwest some 220 million years ago — one of them hunted on land, the other lived in the water.
The victim in this case was an 8-meter-long rauisuchid, a giant carnivorous reptile that was the region’s top terrestrial predator before the rise of the dinosaurs.
Its assailant: a 6-meter phytosaur — an aquatic ancestor of modern crocodiles — that clamped its jaws on the land animal’s thigh, before the prey freed itself, taking one of the phytosaur’s teeth with it.
Each animal is thought to have been the apex predator of its respective habitat, and many scientists assumed that they interacted very little, if at all.
But, according to the paleontologists who found the bone-lodged tooth, their find shows that ancient habitats were by no means isolated, and that many predators — particularly the croc-like phytosaurs — were more promiscuous hunters than had been thought.
“Phytosaurs were thought to be dominant aquatic predators because of their large size and similarity to modern crocodylians,” said Michelle Stocker, a vertebrate paleontologist from Virginia Tech, in a press statement.
“But we were able to provide the first direct evidence that they targeted both aquatic and large terrestrial prey.”
The attack proved not to be fatal: After the croc’s tooth broke off in the struggle, it remained lodged in the rauisuchid’s leg and eventually healed over.
But it wasn’t the only time that the two predators would tangle.
Further analysis of the land reptile’s bones revealed multiple clusters of D-shaped punctures caused by phytosaur bites.
The paleontologists suspect that the rauisuchid suffered — and survived — at least two phytosaur attacks during its lifetime.
“Finding teeth embedded directly in fossil bone is very, very rare,” said Stephanie Drumheller of the University of Tennessee, a collaborator in the research.
“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.” [Read about a similar ‘smoking gun’ from a T. rex: “T. Rex Tooth Found in Dinosaur’s Tail Proves Tyrannosaurus Was a Predator, Study Says“]
The rauisuchid’s bones were found and excavated several years ago near Ghost Ranch, New Mexico, but they were put into storage before they could be prepared and studied.
When the team found the bones, stashed away at the University of California Museum of Paleontology in Berkeley, they soon noticed the signs of violence, and began to investigate.
“We came across this bone and realized pretty quickly we had something special,” said Sterling Nesbitt, also of Virginia Tech.
“There are many bones that get dug up — not all are immediately processed, prepared, and studied.
“No one had recognized the importance of this specimen before, but we were able to borrow it and make our study.”
After discovering the sets of bite marks, the researchers used a CT scanner to peer inside the bone and found the long, embedded tooth.
While the telltale tooth itself couldn’t be extracted, the scientists were able to use the data from the scan to re-create it with a 3D printer.
Aside from the crime-scene investigation aspect of their findings, the research raises bigger questions about what the dynamics of ancient habitats were really like, the paleontologists say.
“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.
“The distinctions between aquatic and terrestrial distinctions were over-simplified, and I think we’ve made a case that the two spheres were intimately connected.”
In particular, their findings raise questions about whether the largest carnivores in the ancient Southwest were also the most dominant.
“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,” Drumheller observed.
“Thus, size cannot be the only factor in determining who is at the top of the food chain.”
“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,” Nesbitt added.
“It goes to show how careful observation can lead to important discoveries even when you’re not seeking those answers.”
The team reports its findings in the German journal Naturwissenschaften.
Drumheller, S., Stocker, M., & Nesbitt, S. (2014). Direct evidence of trophic interactions among apex predators in the Late Triassic of western North America Naturwissenschaften DOI: 10.1007/s00114-014-1238-3