The tooth is broken.
It sits, sharp and unmistakable, lodged in the nasal bone of a duck-billed dinosaur that died 66 million years ago. The tip of the tooth is inside the bone. The base of the tooth snapped off during the bite. The animal that had been carrying the rest of the tooth walked away — leaving the fragment behind as a specific physical record of a moment that would otherwise be entirely lost to time.
The skull belongs to an Edmontosaurus, a common plant-eating hadrosaur of the Late Cretaceous. The tooth belongs, on close analysis, to a Tyrannosaurus.
What the fossil actually preserves
The specimen, catalogued as MOR 1627, was found in eastern Montana in 2005 by fossil hunters working the Hell Creek Formation — the same 66-million-year-old sedimentary layer that has produced most of the world’s best T. rex fossils. The skull is nearly complete and articulated, meaning the bones remained connected as they were in life. It has been housed at the Museum of the Rockies in Bozeman for almost two decades.
In February 2026, a research paper by University of Alberta doctoral student Taia Wyenberg-Henzler and Museum of the Rockies curator John Scannella, published in the journal PeerJ, formally described what makes MOR 1627 extraordinary.
The embedded tooth is the headline finding, but it is not the only one. The skull carries up to 23 additional bite marks from tyrannosaur teeth — a full pattern of damage consistent with a large predator methodically biting the animal’s face. CT scans and detailed measurements of the embedded tooth’s curvature and cross-section identified it as a middle-to-posterior maxillary tooth from an adult Tyrannosaurus. The tooth’s orientation inside the nasal bone shows the bite came from directly in front of the Edmontosaurus. The predator was, in the specific technical sense, biting the herbivore in the face.
Wyenberg-Henzler’s phrase for the analysis has been widely quoted: “kind of like Cretaceous crime scene investigators.” The fossil is unusual in that it identifies not just the victim, but also the attacker.
What it does not preserve
The specific evidentiary limit of MOR 1627 is worth being clear about, because the popular version of the story often skips it.
Around the embedded tooth, there is no healed bone.
In living vertebrates — dinosaurs included — a bite that penetrates bone triggers a specific biological response within days to weeks. Reactive bone tissue called periosteum begins forming around the injury. New mineralized bone accumulates. If the animal survives long enough, the wound remodels visibly. This response is preserved in fossils. It is the specific evidence paleontologists rely on to distinguish attacks that killed their victims from attacks that did not.
MOR 1627 shows no such response. The bone around the embedded tooth is untouched by any healing. Whatever bit this Edmontosaurus, it did so at or near the moment of the animal’s death.
This is where the fossil becomes more ambiguous than the “crime scene” framing suggests.
The absence of healing is compatible with two very different scenarios. The first is that the Tyrannosaurus attacked and killed the Edmontosaurus, biting into its face during a struggle that ended in the herbivore’s death — meaning MOR 1627 preserves the final moments of a successful predatory attack. The second is that the Edmontosaurus was already dead, from some other cause, and the Tyrannosaurus arrived afterwards to feed on the carcass — meaning MOR 1627 preserves not a hunt, but a scavenging event on a corpse.
The fossil cannot distinguish between these possibilities on its own.
Why the ambiguity matters
The specific hunter-versus-scavenger question for Tyrannosaurus has been running in paleontology for over three decades.
One camp, most famously associated with the paleontologist Jack Horner, has argued that T. rex was primarily a scavenger — that its small arms, its enormous olfactory bulbs, and its relatively slow probable running speed all point toward an animal better suited to finding and consuming carcasses than to actively hunting them down. Another camp has argued that T. rex was an active predator, capable of ambushing or pursuing large herbivores and killing them directly.
Most paleontologists now favour a middle position: T. rex was probably an opportunistic feeder, doing both, in proportions that depended on the specific circumstances. But the debate about how often it hunted versus scavenged is not fully settled, and every additional data point matters.
MOR 1627, in isolation, cannot resolve the argument. What it can do is contribute a specific piece of evidence to the broader picture. A 2013 paper by Robert DePalma and colleagues, published in PNAS, described a different Edmontosaurus specimen — this one with a T. rex tooth embedded in a tail vertebra, surrounded by extensively healed bone. That animal had been bitten by a T. rex and survived long enough for the wound to heal, which is direct evidence that at least some T. rex bites were inflicted on living prey. MOR 1627 does not have that healing. It is either a successful kill, or a post-mortem feeding event.
The two fossils together suggest that T. rex was doing both. The DePalma specimen shows attempted predation that failed. MOR 1627 shows either predation that succeeded or scavenging that followed something else’s success.
What one broken tooth still tells us
Even in the absence of a definitive answer, MOR 1627 is genuinely valuable.
The specific location of the bite — the face — is informative. Predators tend to bite the face when trying to control a struggling animal or deliver a killing blow. Scavengers, generally, do not. The 23 additional tyrannosaur bite marks on the skull show a specific pattern of engagement with the head that fits predation more comfortably than casual carcass consumption. The force required to snap a tyrannosaur tooth inside bone indicates a bite pressure at the upper end of what T. rex was capable of — a full-effort attack, not a tentative one.
The most probable reading of the fossil, taken as a whole, is that this Edmontosaurus was killed by a Tyrannosaurus in a face-to-face encounter, though the absence of healing means the alternative interpretation cannot be ruled out.
The tooth is still there. It has been sitting inside the nasal bone of a dead dinosaur for 66 million years. It will presumably remain there, in the display case at the Museum of the Rockies in Bozeman, for as long as anyone keeps taking care of it. Anyone can go and look at it. It is one specific broken piece of evidence from a specific moment at the very end of the age of dinosaurs — a bite delivered so hard that the tooth broke, from an animal that walked away, into the face of an animal that did not.
