Scientists solve 75-million-year-old dinosaur ‘murder mystery’

By Stephen Beech

Tyrannosaurus rex was the ultimate cannibal — feeding on the carcasses of dead relatives, new research reveals.

While tyrannosaurs are often portrayed as fearsome apex predators, a new study has uncovered a more practical side to the King of the Dinosaurs.

State-of-the-art 3D scans of 75-million-year-old bite marks on a foot bone found in Montana show that smaller tyrannosaurs did not shy away from feeding on their deceased relatives.

They didn’t hesitate to act as nature’s scavengers, say scientists, gnawing on the final remains of a carcass.

The study, published in the journal Evolving Earth, was conducted by Josephine Nielsen of Aarhus University in Denmark.

Using 3D scanning, she identified 16 bite marks on a fossilized metatarsal that belonged to a giant T. rex.

Nielsen said: "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."

The study provides fresh insight into how nothing went to waste during the age of dinosaurs and that the hunters were also scavengers.

Nielsen, a master’s student in the department of geoscience at Aarhus University, says the tough foot bones were likely eaten late in the decomposition process, after most of the meat was already gone.

She said: "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."

Nielsen didn't have the original bone in her hands, but instead worked with a digital representation and a 3D-printed version created at Aarhus University.

She said: "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."

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The metatarsal is 3.9 inches (10 centimeters) long and originates from a tyrannosaur that, in life, measured 32 to 39 feet (10 to 12 meters) and weighed several tons.

The bone was found by an amateur fossil hunter in the Judith River Formation — an eroded landscape that serves as a geological archive of a 75-million-year-old ecosystem rich with dinosaur fossils.

The metatarsal has since been donated to the Badlands Dinosaur Museum in Dickinson, North Dakota.

But Nielsen explained that creating a digital copy offered "significant" advantages.

She said: "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 Category-Modifier (CM) 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."

Paleontologist Taia Wyenberg-Henzler and Denver Fowler, curator at the Badlands Dinosaur Museum, both served as Nielsen's external supervisors on the project that sparked the published study.

Nielsen said: "I got in touch with Denver Fowler and Taia 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."

She says the new study confirms that modern technology can help improve understanding of dinosaur behavior with even greater precision.

She added: "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."