75-Million-Year-Old Mystery: Scientists Uncover Tyrannosaurs’ Dark Secret

3D analysis of bite marks on a tyrannosaur foot bone shows that smaller tyrannosaurs scavenged carcasses, likely consuming the final remains after most flesh was gone.

Tyrannosaurs are usually imagined as dominant hunters at the top of the food chain, but new research highlights a more opportunistic side of these massive predators. When the chance presented itself, they also scavenged, feeding on the leftover remains of carcasses rather than relying solely on freshly killed prey.

That conclusion comes from a study conducted at the Department of Geoscience at Aarhus University and published in the scientific journal Evolving Earth.

The research was carried out by Josephine Nielsen, a master’s student at the department. By using 3D scanning techniques, she identified 16 bite marks on a fossilized metatarsal (foot bone) that belonged to a large tyrannosaur more than 75 million years ago.

“I have analyzed the depth, angle, and placement of the marks in a virtual 3D environment and can document that these bite marks did not occur by chance. They are precise impressions from the teeth of a smaller tyrannosaur that fed on a much larger relative,” says Josephine Nielsen.

Fossil Bite Marks Reveal Late-Stage Feeding

The findings offer a glimpse into how dinosaur ecosystems made use of every available resource. Even tough bones could become food late in the decay process, after most of the flesh had already disappeared.

“The bone shows no signs of healing after the smaller dinosaur bites into it. Since the marks are located on the foot, where there is very little meat, it suggests that the dinosaur was ‘cleaning up’ and eating the last remains of an old carcass,” she explains.

Nielsen did not examine the original fossil directly. Instead, she worked with a detailed digital model along with a 3D-printed replica produced at the Department of Geoscience at Aarhus University.

“It would, of course, have been a special experience to work with the real bone, but it is far too risky to send it through the mail to Denmark,” she explains.

Fossil Discovery in Montana’s Judith River Formation

The metatarsal measures 10 centimeters in length and comes from a tyrannosaur that was estimated to reach 10–12 meters long and weigh several tons during its lifetime.

An amateur fossil hunter discovered the bone in Montana’s Judith River Formation, a heavily eroded region that preserves fossils from a thriving dinosaur ecosystem that existed about 75 million years ago. The specimen has since been donated to the Badlands Dinosaur Museum in Dickinson, North Dakota.

Producing a digital version of the fossil also provided important research benefits.

3D Technology Helps Decode Dinosaur Behavior

“What makes this study special is not just the knowledge of how the food chain functioned among dinosaurs millions of years ago, but the technique used to read the details. By creating a digital version, I’ve been able to zoom in on very small details. To ensure the analysis was objective, I used the systematic CM (Category-Modifier) classification system. This method categorizes each individual mark based on fixed criteria, allowing us to distinguish everything from glancing tooth strikes to deep crushing bites. It has been like solving an ancient murder mystery, with metatarsal evidence.”

Canadian paleontologist Taia Wyenberg-Henzler and Denver Fowler, curator at the museum, served as external supervisors on the undergraduate project that eventually led to the published study.

“I got in touch with Denver Fowler and Taia Wyenberg-Henzler while volunteering at an excavation camp in Montana in the summer of 2024. This set me on the path of my project, and it has been incredibly valuable to build international relationships already during my studies,” says Josephine Nielsen.

For Nielsen, the research also demonstrates how modern tools are helping scientists study dinosaur behavior with increasing precision.

“Now we can extract detailed information about their behavior from quite small traces. By using the CM system, we have established a common scientific language to describe bite marks. This means we are no longer just guessing that ‘it looks like a bite’ but can precisely document when and why the small tyrannosaur sank its teeth into the large one,” says Josephine Nielsen.

Reference: “Investigating size-asymmetric feeding among tyrannosaurids using tooth marks on a metatarsal from the Judith River Formation, Montana, USA” by Josephine Nielsen, Denver Fowler, Taia Wyenberg-Henzler, Aase Roland Jacobsen and Christof Pearce, 22 January 2026, Evolving Earth.
DOI: 10.1016/j.eve.2026.100107

Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.