What bite marks on a dinosaur fossil tell us about the T. rex’s eating habits

For decades, dinosaurs, especially the Tyrannosaurus rex, have captured the imaginations of the public and paleontologists alike. In many instances, pop culture has depicted the T. rex as the giant and fearsome hunter that lorded over other dinosaurs.
However, paleontologists have historically disagreed on whether this was actually the case. More recently, scientists have come to the conclusion that, like many modern animals, T. rex was not only an active predator that hunted other dinosaurs for its meals, it also scavenged for its dinner. What was on the menu? How would a T. rex have caught its food? How did they eat? Looking at fossils recovered from the same rocks as T. rex, we can say that plant-eating dinosaurs, such as the horned Triceratops or the duck-billed Edmontosaurus, likely comprised a portion of T. rex’s diet. T. rex bite marks on Triceratops and Edmontosaurus bones certainly support this. However, answering questions about hunting or feeding behaviour is often a lot harder than this. In many cases, it involves some detective work. In some instances, fossilized footprints or bones with bite marks can provide relatively direct evidence of dinosaurs interacting with each other and the environment around them. However, even with these types of fossils, we are often without answers as to how T. rex would have hunted. A recently published study by paleontologist John Scannella and me on a nearly complete Edmontosaurus skull might finally begin to answer this question. Bite marks on a skull On display at the Museum of the Rockies in Bozeman, Mont. is a nearly complete Edmontosaurus skull that provides a fascinating glimpse into T. rex hunting and feeding behaviour. The skull was discovered in 2005 in eastern Montana, on lands managed by the federal Bureau of Land Management. What’s interesting about this particular Edmontosaurus is that a partial tooth tip penetrates directly through the top of the snout into the animal’s nasal cavity, and there are numerous bite marks on both sides of the skull. The penetrating nature of the tooth indicates a powerful bite was delivered to its face. The lack of healing around the embedded tooth suggests that it was embedded after the animal died or, potentially, shortly before it died. CT scans reveal the exact positioning of the tooth within the skull of the Edmontosaurus. Based on its orientation, it appears the tooth broke off when the Edmontosaurus came face-to-face with its attacker. In modern animals, these types of encounters typically result in the death of the animal being bitten. When you combine this with the lack of healing around the tooth and the amount of force needed for the tooth to become lodged into bone, this suggests the Edmontosaurus was unlikely to have survived the encounter. Who bit this Edmontosaurus? Identifying carnivores from bite marks alone is often extremely difficult because the marks rarely preserve information that is specific enough. This is why many bite mark studies often struggle with identifying a specific carnivore. However, carnivorous dinosaur teeth are often more diagnostic, with some teeth being unique to a particular species. Comparing the shape of the serrations and overall size of the tooth to all carnivorous dinosaurs that lived alongside the Edmontosaurus tells us that a Tyrannosaurus was responsible. How big was the Tyrannosaurus? We answered this by comparing the size of the serrations on the embedded tooth to the serrations of teeth still attached in the skulls of different Tyrannosaurus individuals paleontologists have unearthed. We found that the tooth would have come from an adult Tyrannosaurus, with a skull about one metre long. What do these bite marks tell us? The presence of bite marks on the skull suggests that the Edmontosaurus wasn’t just killed by the Tyrannosaurus. It was eaten too. Looking at the position of the bite marks provides information about the behaviour of the carnivore that produced them. On the Edmontosaurus skull, the bite marks are located on the right side of the skull, in the region behind the eye, while on the left side bite marks are located along the back third of the bottom jaw. In duck-billed dinosaurs like the Edmontosaurus the back third of the skull is where most of the major chewing muscles are located and would have been the area with the greatest amount of flesh on the skull after the rest of the soft tissue on the body had been eaten. Modern carnivores typically eat the parts of a carcass that have the greatest amount of flesh, such as the limbs and internal organs, and gradually work their way to areas with the least amount of flesh, such as the skull and feet. Because the Edmontosaurus is represented by only the skull, this suggests that the Tyrannosaurus would have removed most of the flesh off the carcass before parts of it became washed away and buried. To have direct fossil evidence that a dinosaur had likely been killed and then eaten, and to be able to say it was a Tyrannosaurus that killed it, is exceptionally rare. A fossil like this gives us an important glimpse into the potential hunting behaviours of large carnivorous dinosaurs.

Taia Wyenberg-Henzler does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.