Thousands of fossilized bones from a Cretaceous bonebed in Wyoming have handed paleontologists something rare: physical traces of how Tyrannosaurus rex interacted with the bodies of its prey. Rather than a dramatic hunting scene, the evidence points largely to feeding on carcasses. The study also produced a practical byproduct, a tightened set of standards for deciding when a mark on ancient bone was truly left by a predator’s tooth.
A Wyoming bonebed packed with duck-billed dinosaurs
The material came from a bonebed dating to between roughly 72 and 66 million years ago, dominated by remains of Edmontosaurus annectens, a duck-billed dinosaur. Bonebeds like this preserve large numbers of individuals in one place, giving researchers a statistical sample rather than a single skeleton. That volume matters, because feeding traces are uncommon and easy to confuse with other kinds of damage. Working through such a dense deposit allowed the team to search systematically for the subtle scars that a large theropod might leave behind while feeding, an approach detailed in the study report.
Just 12 bones out of more than 3,000
The scarcity of clear evidence is one of the study’s most telling results. Researchers examined more than 3,000 bones and found only 12 that carried possible tooth traces. Of those, four showed patterns that closely matched the shape and spacing expected from Tyrannosaurus rex teeth. That small yield underscores how rarely feeding marks survive on fossil bone, and it cautions against assuming that every scratch or pit on an ancient bone is a bite. The overwhelming majority of the bones in the deposit carried no convincing tooth marks at all.
Matching the marks to a specific predator
Identifying the culprit required comparing the marks against the animals known to have lived in the same ecosystem. By measuring the spacing between the traces and weighing that against the tooth structure of local predators, the researchers concluded that Tyrannosaurus rex was the most likely source. The reasoning is comparative rather than eyewitness: a mark that fits the size, shape and spacing of a T. rex bite, in an environment where that animal lived, points to it more strongly than to any smaller-toothed contemporary. The analysis stopped short of claiming certainty, framing the tyrant dinosaur as the best-supported candidate, as laid out in a summary of the bite-mark analysis.
Signs of scavenging rather than a fresh kill
The condition of the bitten bones shaped the interpretation of behavior. Most of the marked bones showed no signs of healing, which indicates the animals were bitten around the time of death or afterward. Healed bone would suggest a victim that survived an attack, evidence of active predation on a living animal. The absence of healing instead points toward feeding on carcasses, meaning the marks are more consistent with scavenging than with a chase and takedown. That distinction feeds into a long-running discussion about how much of the T. rex diet came from hunting versus opportunistic feeding on animals that were already dead.
What the marks say about feeding on carcasses
Read together, the traces sketch a picture of a large predator working over the bodies of duck-billed dinosaurs, leaving occasional gouges on bone as it stripped flesh. The rarity of the marks is consistent with a feeder that concentrated on soft tissue and only intermittently scored the underlying skeleton. None of this rules out that Tyrannosaurus rex also hunted living prey; it simply shows that, in this particular deposit, the recoverable evidence documents carcass feeding. The findings add a concrete data point to reconstructions of how the animal actually used its powerful jaws on the remains it encountered.
A sharper checklist for reading tooth traces
Beyond the specific case, the researchers used the Wyoming bonebed to refine broader scientific standards for identifying tooth traces on fossil bone. The resulting checklist weighs the shape, depth, edges and location of a mark against the natural anatomy of the animal in question, and against the damage that can be produced by disease, decay and burrowing insects. That framework is meant to reduce false positives, since many processes can leave pits and grooves that superficially resemble bites. By formalizing the criteria, the study gives other paleontologists a repeatable method for distinguishing genuine feeding traces from lookalikes, work that is described further in independent coverage of the research.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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