T. rex leaves its signature on Wyoming fossils, and on a long-running debate about who bit whom

A collection of fossilized dinosaur bones pulled from the Lance Formation in eastern Wyoming carries bite marks that a peer-reviewed study published on 15 July 2026 attributes to Tyrannosaurus rex. The marks, gouged into ribs, vertebrae and other skeletal fragments dated to the final stretch of the Cretaceous, are the latest physical evidence in a debate that has run for decades: when T. rex teeth show up on a bone, does that prove a hunt, a scrape over a carcass, or simply that nothing else on the landscape could have made such a wound?

The short answer, the authors argue, is that a T. rex bite is its own signature, and the Wyoming assemblage bears that signature often enough to deserve its name in the paper. The longer answer sits inside a broader argument about which carnivores ruled the last North American ecosystems before the asteroid, and about how reliably palaeontologists can read a predator from a puncture wound left behind in stone.

What the bones actually show

The study, summarised by Phys.org on 15 July 2026, examined a curated assemblage of dinosaur fossils from Wyoming's Lance Formation, a rock unit laid down in the closing millions of years of the Cretaceous Period. The team catalogued tooth marks across multiple skeletal elements and compared their shape, spacing and depth against the known dental profiles of large theropods that shared the habitat.

The match pointed repeatedly to T. rex. The widths and spacing of the marks, the puncture geometry, and the way some gouges tracked along bone surfaces lined up with what a tyrannosaur jaw would produce, and not with the dentition of contemporaneous smaller predators. That matters because the Lance Formation has long been a graveyard for mixed faunas: hadrosaurs, ceratopsians, ankylosaurs, smaller theropods, and the occasional tyrannosaur carcass itself.

For each marked bone, the researchers asked two questions: could a tyrannosaur have produced the wound, and could anything else credibly have done so instead? In enough cases, the answer pointed one way. The paper's argument is not that every mark on every bone belongs to T. rex, but that the proportion of marks consistent only with a tyrannosaur jaw is too high to be coincidence.

A stubborn alternative reading

Not everyone in the field will be persuaded. The competing view, common in the literature for years, holds that surface marks on bone are ambiguous: a feeding scavenger, a trampling animal, or even geological pressure can mimic tooth-shaped damage, and assigning any single wound to a single species overstates the evidence.

The new study pushes back on that scepticism by leaning on statistical clustering rather than on any one dramatic puncture. A single ambiguous gouge is easy to dismiss. A bonebed in which a recognisable tyrannosaur bite signature appears across multiple elements, at frequencies well above what random taphonomy would predict, is harder to wave away. The authors are explicit that some marks in the assemblage cannot be securely attributed, and they say so. The claim is one of predominance, not monopoly.

A secondary critique runs the other direction: if T. rex really did range across the Late Cretaceous floodplains of Wyoming in numbers implied by its fossil record, why are unambiguous T. rex bite marks so rare on most other Lance Formation bones? The honest answer, the paper suggests, is sampling. Most fossil bone is weathered, mineralised beyond diagnostic detail, or comes from museum drawers never re-examined with current comparative metrics. The Wyoming assemblage in this study was selected and re-imaged precisely to test that question.

Why a tooth mark is harder to read than it looks

Assigning a bite mark to a species is an exercise in reverse engineering. The trace left on bone depends on tooth shape, jaw geometry, bite force, the angle of approach, and what the bone was doing at the moment of contact: was it still in a living animal, freshly stripped of flesh, or already drying in the sun? Each variable bends the resulting wound in a different direction.

Modern methods lean on high-resolution surface scanning, comparative bite-mark libraries built from extant carnivores, and statistical models that weigh the probability of one assignment against another. The Wyoming team used a version of that workflow, scoring marks against a reference set drawn from T. rex and the other large theropods known from the same formation. Where the score crossed a threshold, the mark was assigned. Where it did not, the mark was left unattributed. That discipline is what gives the headline claim its weight: the paper is not claiming certainty, only that a defensible threshold of probability has been crossed.

What it changes, and what it doesn't

If the attribution holds, it adds another data point to the case that T. rex was not merely a hunter of large prey but an opportunistic feeder that handled carrion as well. Bite marks on already-stripped bones, on skeletal elements a predator would not normally target for meat, and on bones from species T. rex is unlikely to have brought down alive all push in that direction. The picture of the Cretaceous food web sharpens accordingly: an apex carnivore that also functioned as the ecosystem's clean-up crew.

The finding does not resolve every older dispute. It does not prove T. rex was a social hunter, nor that it was exclusively a scavenger, nor that other large theropods were absent from the same scavenging niche. It does tighten one specific link in a long chain of inference, and it gives the next round of Wyoming bonebed work a benchmark to test against. The forthcoming question for the field is whether other Lance Formation assemblages, re-scanned with the same protocol, replicate the pattern or expose it as a local artefact.

For now, the bones themselves are the cleanest evidence. They sat in the ground for roughly 66 million years before being lifted into daylight, and the marks on them are finally being read with tools their discoverers did not have. The signature is consistent enough to put T. rex's name on the wound, and that is a tighter claim than the field has been willing to make for some time.

The desk covered this story as a discrete piece of palaeontological inference rather than as a broader feature on Cretaceous ecosystems. The reporting foregrounds the comparative dental analysis rather than the surrounding media coverage, which has tended to compress the statistical argument into a single sentence.