Thousands of fossilized bones from a Cretaceous-period bonebed in Wyoming, the United States, offer rare physical evidence that Tyrannosaurus rex fed on the carcasses of a duck-billed dinosaur species called Edmontosaurus annectens.
Life reconstruction of Edmontosaurus annectens. Image credit: Dani Navarro.
“Identifying the origin of perforating lesions on fossil bone is often difficult, and many are considered tooth traces, in spite of more likely and more parsimonious etiologies,” said Loma Linda University paleontologist Bethania Siviero and colleagues said.
“Much of this confusion stems from tooth trace criteria that are ambiguous when the context for the lesions is not considered.”
“Mistaken identification of tooth traces has led to misleading interpretations of animal behavior.”
“Our study of tooth traces on fossil bones critically reviews previous criteria.”
In their research, Dr. Siviero and co-authors examined 3,013 bones excavated between 1997 and 2017 from a paleontological site near Hanson Ranch Station in northeastern Wyoming, part of the Lance Formation.
The bones belonged overwhelmingly to a single species of large plant-eating hadrosaur, Edmontosaurus annectens.
Only a small fraction of the bones — thirteen out of 3,013 — showed marks resembling tooth traces.
After closer analysis, including CT scans, the paleontologists determined that one of those was not a bite mark at all but a natural anatomical feature.
A Late Cretaceous face-off between an adult Nanotyrannus lancensis (left) and two juvenile Tyrannosaurus rex, with a sub-adult Tyrannosaurus rex watching from a distance. Image credit: Jorge Gonzalez.
Of the twelve bones confirmed to bear genuine tooth traces — including ribs, vertebrae, a radius and an ulna — four preserved distinctive patterns attributable to two known ichnospecies, Knethichnus parallelum and Linichnus serratus.
By comparing the spacing of these marks to the tooth structure of predators known to have lived in the same ecosystem, the researchers concluded that Tyrannosaurus rex was the most likely source of the bite marks.
Most of the bitten bones showed no signs of healing, suggesting the animals were bitten around the time of death or afterward — evidence of scavenging rather than active predation.
The scientists also used the Wyoming bonebed to refine broader scientific standards for identifying tooth traces on fossil bones.
“Correctly identifying bone depressions and perforations is important because not all of these features are tooth marks,” they said.
Their findings were published online today in the journal PLoS ONE.
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B.C.T. Siviero et al. 2026. Identification of tooth traces from a Cretaceous (Maastrichtian) Edmontosaurus annectens bonebed in the Lance Formation, Wyoming, U.S.A. PLoS One 21 (7): e0351939; doi: 10.1371/journal.pone.0351939
