A broken Tyrannosaurus rex tooth sits embedded in the face of an Edmontosaurus skull pulled from the Hell Creek Formation in eastern Montana, preserving the physical record of a predator’s bite that happened roughly 67 million years ago. The prey never healed. Researchers affiliated with the Museum of the Rockies at Montana State University and the University of Alberta matched the tooth to T. rex after comparing it against every known meat-eating dinosaur from the same geological deposit, and their findings are now published in PeerJ. The specimen offers direct, bone-level evidence that T. rex attacked living prey and that at least some of those strikes killed quickly.
Why the absence of healing changes the T. rex hunting debate
The core finding is stark: CT scans performed at a Bozeman medical imaging facility showed no reactive bone growth around the tooth fragment lodged in the Edmontosaurus face, according to institutional reporting on the study. In living bone, the body begins laying down new tissue around a foreign object within days. The complete absence of that response means the Edmontosaurus did not survive long enough for even early-stage repair to begin, a window that in modern animals typically closes within roughly two weeks.
That timeline matters because it separates this specimen from previously documented cases. A peer-reviewed study published in the Proceedings of the National Academy of Sciences had already shown that embedded theropod teeth in hadrosaur bones sometimes appear alongside reactive bone growth, proving the prey survived the initial attack and lived long enough for tissue to respond. Those cases demonstrated that T. rex bit living animals but left open the question of how often such bites were immediately fatal. The new Montana specimen fills in the other half of that picture: a bite to the face with no survival period at all.
The hypothesis that T. rex facial strikes frequently produced rapid fatal injuries rather than prolonged chases gains support here, though one specimen cannot establish frequency on its own. What it does establish is that the killing mechanism was not limited to pursuit and exhaustion. A single bite to the skull could end the encounter outright, especially when delivered by an animal whose bite forces have been estimated in other work using methods archived through biomedical databases.
How researchers matched the tooth to Tyrannosaurus rex
The fossil was discovered in 2005 on land managed by the Bureau of Land Management in the Hell Creek Formation of eastern Montana, according to a Bureau of Land Management account of the find. It was later prepared and put on display at the Museum of the Rockies in Bozeman. For years, the embedded tooth was visible but unidentified. The new PeerJ paper changed that by running a systematic comparison.
The research team, with members at the Museum of the Rockies, Montana State University, and the University of Alberta, measured the broken tooth and compared its size, shape, and serration pattern against every known theropod species recorded from the Hell Creek Formation. That formation preserves the final chapter of non-avian dinosaur life in North America, and its predator roster includes several smaller meat-eaters alongside T. rex. The tooth matched only Tyrannosaurus rex, ruling out other candidates.
CT imaging at a medical facility in Bozeman allowed the team to examine the tooth tip and surrounding bone without cutting into the fossil. The scans confirmed the tooth had snapped off inside the Edmontosaurus face during the bite, consistent with the kind of breakage that occurs when a predator strikes bone at high force. T. rex teeth were built to withstand enormous bite pressures, but individual teeth broke regularly and were replaced throughout the animal’s life. A snapped tip left behind in prey is, in effect, a biological calling card.
What the fossil does and does not settle about T. rex predation
The specimen strengthens the case that T. rex was an active predator, not merely a scavenger that fed on animals already dead. The scavenger-versus-predator debate has persisted for decades in paleontology, and evidence has accumulated on the predator side through multiple lines of inquiry. Healed bite marks on prey bones show animals survived T. rex attacks and lived afterward, which can only happen if the prey was alive when bitten. The Montana Edmontosaurus adds a complementary data point: an attack where the prey did not survive, with the weapon still in place.
The conflict between the two types of embedded-tooth evidence, healed and unhealed, is not a contradiction. It reflects a range of outcomes from predatory encounters. Some prey escaped and recovered. Others did not. Both scenarios confirm predation rather than scavenging, because a scavenger biting a carcass would not produce the kind of forceful, bone-penetrating strike that snaps a tooth and lodges it deep in facial bone. In a carcass, soft tissues give way more readily, and the mechanical resistance that breaks teeth is lower.
The new fossil also adds nuance to reconstructions of T. rex behavior. A face bite implies close-quarters engagement, not a tentative nip at the flanks. Striking the head of a large herbivore like Edmontosaurus carries risk: the prey can fight back with its own mass and momentum. That T. rex regularly accepted that risk is consistent with a predator adapted to subdue large, dangerous animals rather than relying on already-dead carrion.
Still, the specimen does not end the debate over how often T. rex scavenged. Most large carnivores today both hunt and scavenge, and there is no reason to think Tyrannosaurus was different. The Edmontosaurus skull shows one instant in time when a hunt ended in a rapid kill. It cannot reveal how frequently T. rex also exploited carcasses, or whether scavenging played a larger role at certain life stages or in particular environments.
Limits of a single dramatic specimen
Several questions remain open. The full text and figures of the PeerJ paper have only recently become available, and independent researchers have not yet had time to scrutinize the CT data or the comparative tooth measurements in detail. The exact location coordinates from the 2005 discovery remain unpublished in BLM field records, limiting the ability of other teams to study the surrounding sediment for additional context about the attack site. No associated trackways, bite-marked bones from other individuals, or clear signs of a kill site have been reported from the immediate area.
Sampling bias is another concern. The Hell Creek Formation has yielded thousands of fossils, but only a fraction preserve interactions between species with the clarity of an embedded tooth. The absence of similar finds in other quarries could reflect genuine rarity of fatal facial bites, or it could simply result from the low probability of preserving a tooth in exactly the right place and orientation. Until more specimens like this one are documented, researchers have to be cautious about extrapolating broader behavioral patterns.
There is also the issue of identification confidence. While the comparative analysis points strongly to T. rex as the only plausible source for the tooth, paleontologists work with incomplete rosters of species. A yet-unknown large theropod from the same time and place is unlikely but not impossible. Future discoveries could slightly reshape the predator lineup in late Cretaceous North America and prompt re-evaluation of isolated finds like this one.
Even with these caveats, the Edmontosaurus skull with its embedded Tyrannosaurus tooth stands out as one of the clearest snapshots of a lethal interaction between two dinosaurs. It captures not just who bit whom, but when in the sequence of life and death that bite occurred. With no healing and the broken weapon still locked in bone, the fossil records the moment a living animal crossed the threshold into being a carcass, one crushing bite at a time.
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*This article was researched with the help of AI, with human editors creating the final content.
