Out of more than 3,000 fossilized dinosaur bones pulled from a single Wyoming quarry, only four carry a mark researchers are confident came from a Tyrannosaurus rex's teeth. That number, small enough to count on one hand, is the actual headline of a study published July 15, 2026, in the open-access journal PLOS One, and it says as much about the difficulty of reading ancient bite marks correctly as it does about how T. rex actually behaved 66 million years ago.

A quarry full of duck-billed dinosaurs, and a scientific problem

The research, led by Bethania C. T. Siviero of Loma Linda University alongside colleagues Elizabeth Rega, Matthew A. McLain, Leonard R. Brand, David Nelsen, and Art V. Chadwick, examined bones recovered over more than two decades of digging at a fossil site in the Lance Formation of northeastern Wyoming, rock laid down during the final stretch of the Cretaceous period roughly 66 to 72 million years ago. The vast majority of bones pulled from the site belonged to Edmontosaurus annectens, a large, duck-billed plant-eating dinosaur that appears to have died in significant numbers at this particular location.

Bite marks preserved directly in fossil bone represent one of paleontology's rarest and most valuable forms of direct evidence, offering researchers a genuine window into how prehistoric predators actually behaved, what they ate, and whether they hunted living prey or scavenged carcasses already dead, insights that are otherwise nearly impossible to reconstruct from skeletal anatomy alone. But that same rarity and value comes with a serious catch: identifying a genuine tooth mark correctly is considerably harder than it might seem.

Why so few marks survived scientific scrutiny

Of the more than 3,000 bones examined, only 12 carried features that even resembled potential tooth traces, punctures, grooves, and other depression-like marks that could plausibly have come from a predator's bite. Of those 12 candidates, the research team ultimately confirmed only four as genuine tooth marks specifically attributable to T. rex based on rigorous comparative analysis. The remaining eight either showed characteristics consistent with other causes entirely, or couldn't be confidently attributed to any specific predator species.

That steep drop-off, from 3,000 total bones down to just four confirmed T. rex bites, reflects a persistent and underappreciated challenge in paleontology. As the study's authors put it directly, "correctly identifying bone depressions and perforations is important because not all of these features are tooth marks." Disease processes, insect activity, natural bone erosion after death, and even ordinary anatomical openings that once carried nerves or blood vessels during the animal's life can all produce marks that superficially resemble a predator's bite, and mistaking one for the other has historically led researchers toward shaky or outright incorrect conclusions about how extinct animals actually lived, hunted, and died.

The specific technique that separated real bites from lookalikes

To distinguish authentic T. rex bites from these various lookalikes, the research team leaned on a specific anatomical detail: the serrated structure of tyrannosaur teeth. Many meat-eating dinosaurs, T. rex included, had blade-shaped teeth lined with tiny serrated points called denticles, and when such a tooth drags across bone during a bite, it can leave behind parallel scratches that faithfully record the precise spacing between those denticles. Siviero explained the underlying logic to Earth.com: "Teeth with denticles exhibit spacing between adjacent denticles that can be diagnostic at the species level," meaning the spacing pattern itself functions almost like a species-specific signature left directly in the bone.

The clearest of the confirmed bites went beyond simply denting the bone's surface; they preserved fine, measurable serration patterns detailed enough to compare directly against known tyrannosaur tooth morphology. One particularly distinctive mark identified by the research team carries the formal ichnotaxon designation Linichnus serratus, a specific classification used to describe this recognizable pattern of serrated tooth-drag scoring.

A convincing bite that turned out to be no bite at all

Perhaps the most revealing episode in the entire study involves a specimen that initially seemed like one of the clearest cases in the collection, and turned out to be nothing of the sort. Researchers had identified 47 bones from the site classified as Edmontosaurus surangulars, a specific bone forming part of the lower jaw. One specimen among those 47 stood out immediately because its overall shape didn't quite match the others, and it carried what appeared to be convincing puncture marks. Because loose crocodilian teeth had already turned up elsewhere at the same site, a crocodile bite initially seemed like the obvious, straightforward explanation for those punctures.

A CT scan changed the entire interpretation. The scan revealed that the supposed bite punctures were actually natural anatomical openings, not tooth marks at all. Even more surprisingly, comparing the bone's overall shape against specimens held in two separate museum collections revealed it didn't belong to an Edmontosaurus in the first place. It came instead from a triceratopsin, the broader horned-dinosaur group that includes both Triceratops and Torosaurus, and the fossil most closely matched the jawbone of a specific named specimen known as "Billy," a subadult Torosaurus. Researchers couldn't confirm the bone belonged to that exact genus with full certainty, so they classified it more conservatively as a triceratopsin generally, but the misidentification itself, mistaking both the bone's owner and the nature of its markings, stands as a pointed illustration of exactly the kind of interpretive trap the study's broader methodology was designed to help paleontologists avoid.

What the confirmed bites reveal about T. rex behavior

Among the bones with genuinely confirmed tooth marks, researchers found no evidence of any healing around the wounds, a detail that carries real behavioral significance. Healed bone around a bite mark would indicate the animal survived the initial injury for some period of time; the absence of healing here instead suggests the marks were made either at or after the time of the animal's death. That pattern, combined with earlier research already conducted at the same site, points toward a broader scenario in which at least some of these Edmontosaurus individuals may have been actively predated by T. rex, while their carcasses were also likely scavenged and exposed to the elements for a period before eventual burial and fossilization, a dual pattern of both hunting and opportunistic scavenging rather than one clean behavioral story.

Why a rigorous identification method matters beyond this one bonebed

Beyond the specific findings at this Wyoming site, the study's broader contribution lies in establishing more rigorous, explicit criteria for evaluating potential tooth traces generally, a methodological framework the authors argue has been inconsistently applied across prior paleontological research. As the researchers noted, "much of this confusion stems from tooth trace criteria that are ambiguous when the context for the lesions is not considered," and their study explicitly set out to critically review and refine those existing criteria rather than simply cataloging another set of bite marks.

That distinction matters for the field well beyond this single Wyoming quarry. Bite mark identification has previously informed high-profile interpretations of dinosaur behavior, including earlier, separate research identifying T. rex tooth marks on the bones of other tyrannosaurs, interpreted by some researchers as evidence of cannibalistic behavior. Given how much interpretive weight a single confirmed or misidentified bite mark can carry in reconstructing an extinct ecosystem's predator-prey relationships, a more rigorous, serration-spacing-based standard for confirming genuine tooth traces gives paleontologists a considerably more reliable tool for building future behavioral conclusions on firmer ground, rather than risking another convincing-looking mark turning out, on closer inspection, to be nothing more than an ordinary anatomical feature or an entirely different animal's bone altogether.

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*Sources cited in this article include the peer-reviewed study "Identification of tooth traces from a Cretaceous (Maastrichtian) Edmontosaurus annectens bonebed in the Lance Formation, Wyoming, U.S.A.," published July 15, 2026, in PLOS One, and reporting from ScienceDaily, EurekAlert, Phys.org, SciTechDaily, Earth.com, Discover Magazine, Sci.News, and Popular Science covering research led by Bethania C. T. Siviero of Loma Linda University. All figures reflect reporting available as of August 6, 2026.*