One day, between 72 and 66 million years ago, a herbivorous dinosaur became tyrannosaurus rexfood. Several fossilized bones discovered in Wyoming during several excavations between 1997 and 2017 feature tooth marks that were likely the result of a large bite from a tyrannosaurus rex. The fossils are detailed in a study published today in the journal PLUS oneand they are helping paleontologists reconstruct an extinct ecosystem.

“The study of tooth marks on fossil bones is important because it provides valuable information about animal behavior and interactions between species,” the study authors wrote in a joint statement.

In the study, authors Bethania CT Siviero, Elizabeth Rega, Matthew A. McLain, Leonard R. Brand, David Nelsen and Art V. Chadwick examined more than 3,000 bones found in northeastern Wyoming. They date back to between 72 and 66 million years ago, during the late Cretaceous period. Most of the bones were Edmontosaurus annectensa large duck-billed herbivorous dinosaur that lived in present-day western North America.

Of the 3,013 bones studied, only 12 had remains of teeth. Four had distinct patterns of tooth marks, and based on the spacing and shape of these marks, the team believes they are the result of a tyrannosaurus rex bite. Some of the other tooth traces may have been created by other carnivorous dinosaurs and crocodiles.

Importantly, most teeth-marked bones do not have any evidence of healing. This means that the marks were probably made around or after the animals’ death. The animals may have been hunted while they were alive, or a larger carnivore may have scavenged their carcasses after they died. The remaining bones were buried and fossilized for tens of millions of years.

To assist future researchers, the study also includes a tooth mark guide that describes and identifies various types of punctures, holes, and other marks on fossils that appear to be tooth marks.

On fossils, tooth marks often look like punctures or grooves. However, similar marks can form on bones for a number of other reasons, including joint diseases or erosion after the animal dies. To study prehistoric ecology and animal behavior using bite marks, scientists must make sure that what they are actually seeing are bite marks. Establishing a set of criteria for identifying tooth marks on fossil bones could be a vital paleontological research tool.

“It is essential to distinguish between these different types of bone modifications, as they can provide valuable information about the condition of an animal before death, as well as the processes that affected its remains after death,” the authors concluded.

Who knows what other evidence of dinosaur food may be lurking deep in the ground waiting to be unearthed. However, that duck-billed dinosaur might complain about how precious its death 72 million years ago was.

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