Fossilized dinosaur bones unearthed in Wyoming carry tooth marks likely left by Tyrannosaurus rex, according to a July 2026 study published in PLOS One. Concurrently, new biomechanical experiments reveal that 13-year-old juvenile tyrannosaurs could exert up to 5,641 newtons of bite force, shedding fresh light on how teenage predators hunted.
Uncovering Cretaceous Bite Marks in Wyoming
Paleontologists examining more than 3,000 Cretaceous bones collected in northeastern Wyoming have uncovered physical evidence of prehistoric feeding behaviors. The fossils, dating to the late Cretaceous period roughly 72 to 66 million years ago, primarily belonged to Edmontosaurus annectens—a large, plant-eating dinosaur known for its broad, duck-shaped bill. Out of thousands of specimens, scientists identified 12 bones bearing possible tooth traces, with four displaying distinctive patterns that matched the expected shape and spacing of Tyrannosaurus rex teeth.
The research, led by Bethania C. T. Siviero of Loma Linda University, was published on July 15, 2026, in the open-access journal PLOS One. Distinguishing genuine predation from other natural degradation is a central challenge in paleontology. Bones can suffer punctures and grooves from disease, weathering, insect activity, and post-mortem erosion. To establish clearer criteria, the team analyzed various depressions and holes, creating a practical framework for identifying true tooth damage.
“The study of tooth marks on fossil bones is important because it provides valuable insights into animal behavior and interactions between species.”
Study authors, via ScienceDaily
Feeding and Scavenging in Ancient Ecosystems
Most of the marked bones analyzed in the PLOS One research showed no signs of surrounding tissue healing. This critical detail suggests that the biting events occurred either at the time of death or after the animals had already perished. Combined with earlier excavations at the same fossil site, the findings indicate that predators likely killed some of the prey animals before scavengers moved in to feed on exposed carcasses prior to eventual burial and fossilization.
While T. rex emerged as the most probable biter for the four distinctive specimens, researchers noted that other carnivorous dinosaurs and local crocodilians also inhabited the region. These competing predators and scavengers likely contributed to the broader array of damage observed across the fossil assemblage.
Testing the Bite Force of Teenage Tyrannosaurs
While adult tyrannosaurs possessed bone-crushing jaws, understanding how teenagers hunted has long challenged researchers. To measure adolescent capability, Jack Tseng of UC Berkeley and Joseph Peterson of the University of Wisconsin in Oshkosh built a metal replica of a scimitar-shaped tooth from a 13-year-old juvenile T. rex. Mounting the cast on an engineering mechanical testing frame, the team attempted to crack cow legbones.
Based on 17 successful trials that accurately replicated fossil bite marks, the researchers determined that a juvenile T. rex could exert up to 5,641 newtons of force
. That capacity places teenage tyrannosaurs in a distinct ecological weight class—operating somewhere between the jaw forces exerted by modern hyenas and crocodiles.
Previous estimates derived purely from muscle reconstruction or scaled-down adult measurements had suggested a weaker bite of around 4,000 newtons. The experimental findings Berkeley demonstrate that younger animals were actively strengthening their jaw muscles and refining their techniques long before their adult teeth emerged.
Fossil Skulls and Ecological Roles
The experimental setup relied on physical evidence discovered years earlier in the Hell Creek Formation of eastern Montana by Peterson. Among the finds was the skull of a juvenile T. rex bearing a healed bite mark on its face—an injury attributable to another T. rex during a violent clash over food or territory.
| Tyrannosaur Stage | Bite Force | Tooth Shape | Primary Function |
|---|---|---|---|
| Juvenile (approx. 13 years) | Up to 5,641 newtons | Oval, knife-like | Cutting and tearing flesh; puncturing bone |
| Adult (30 to 40 years) | About 35,000 newtons | Round cross-section, post-like | Crushing bone |
Juvenile teeth featured oval cross-sections tailored for slicing flesh, whereas adults developed robust, post-like teeth designed to crush bone. By combining fossilized tooth traces from Wyoming with biomechanical modeling from California and North Carolina, paleontologists are constructing a clearer timeline of how these predators grew, competed, and filled distinct ecological niches across millions of years.
