Kent Hups set out one morning on a research expedition in the famed Hell Creek Formation, a series of fossil-rich sedimentary rock layers in the western United States. The vast formation, spanning parts of Montana, Wyoming, North Dakota and South Dakota, is abundant in Late Cretaceous dinosaur bones — but finding footprints is a different story. The area’s sediments typically eroded before the tracks could be preserved. Yet Hups, a high school science teacher from Northglenn, Colorado, found himself looking down at what ended up being the first known trackway left behind by a T. rex. “My first reaction was total disbelief,” said Hups, a volunteer research associate at the Denver Museum of Nature & Science. “I sat and looked at it for a period of time before I was convinced it was a track at all.” The two giant footprints he initially spied in July 2025 had distinct three-pronged impressions strikingly similar to other fossilized tracks. To determine which Cretaceous species would have left the marks, he measured the trace fossil from end to end. Footprints with a length that’s greater than the width suggest the track maker was likely a meat eater, Hups explained. With each footprint about 3 feet (0.9 metre) long and 2 to 2½ feet (0.6 to 0.8 metres) wide, Hups spotted evidence not only for a carnivore but the largest, most iconic meat-eating dino that lived in what once was a lush, swampy coastal floodplain — Tyrannosaurus rex. The extraordinary footprints are described in a study published September 8 in the Journal of Vertebrate Paleontology. Unlike bones, these tracks capture live movement from 66.5 million years ago, offering clues to the prehistoric apex predator’s behavior and walking stride, researchers say. “I hope that more people go out and look a little bit harder at those strange looking rocks and this leads to a better, more detailed understanding of what life looked like in the past,” Hups said in an email. “It is the closest thing that we have to a time machine.” First found T. rex trackway Hups, a coauthor of the new report, had found two fossilized footprints out in the open, one more eroded than the other, but study coauthor Tyler Lyson, senior curator of vertebrate paleontology at the Denver Museum of Nature & Science, was looking for stronger evidence of a pattern to be convinced this was a dinosaur trackway. “Rocks can weather into all different shapes and sizes, you know, some that look like Florida, some that look like Texas, some that look like T. rex footprints,” Lyson said. Lyson marked an X in the dirt where other footprints should have been. As the researchers dug, they not only found a third, but a fourth print as well. The prints had three slender toes and the middle digits were longer than the others, an anatomy similar to T. rex feet. Also, the size was a key indicator, Lyson said. The Hell Creek Formation “is one of the best studied rock units in the world, so we think we have a really good understanding of what dinosaurs were living there, and the two dinosaurs that are big enough to make such a track are T. rex and then the duck-billed dinosaur called Edmontosaurus,” he said. “Their feet are very different.” The four footprints are noted in the study. But this summer, the research team located a fifth print. “So, there’s no doubt in my mind that it’s a trackway that belongs to a T. rex,” Lyson said. The discovery was a result of the dinosaur being in the right place at the right time, he added. What’s now North Dakota was a plant-rich environment where dinosaurs could thrive 66.5 million years ago. The soft, muddy earth created the conditions needed for the dinosaur tracks to be buried, brought back to the surface and exposed by erosion. Previously, researchers had found only two isolated footprints attributed to the tyrannosaur. The first specimen was discovered by a US Geological Survey geologist in New Mexico and described in 1994, and the second was reported in a study by a University of Manchester paleontologist in 2008 from the Hell Creek Formation in Montana. Scientists have unearthed only a handful of tracks from other dinosaurs in the wider Hell Creek Formation. “Worldwide, trackways aren’t that rare, but for this interval of time in North America, they’re very rare,” Lyson said. Longer and more clearly preserved trackways from other large meat-eating dinosaurs are known elsewhere, but the first trackway likely attributable to T. rex is important, noted Dr. Anthony Romilio, a paleontologist and research associate with the University of Queensland’s Dinosaur Lab in Brisbane, Australia. Romilio was not involved with the study. In the Hell Creek Formation, “even a poorly preserved example is a meaningful discovery there,” Romilio wrote in an email. “Any trackway provides a record of real behaviour that their bones cannot: a few seconds of life, 66.5 million years ago.” T. rex trackway reveals clues on the dino’s gait Dozens of T. rex skeletons have been uncovered in the Hell Creek Formation, which preserves evidence of North America’s last dinosaur ecosystem. But tracks can give scientists clues that bones can’t, including how fast the dinosaur was moving and what its feet may have looked like. Multiple tracks can provide more information than isolated footprints and allow scientists to estimate how fast an animal was moving when its tracks formed. In this case, the new trackway discovery provides the first direct evidence of a T. rex’s stride length — about 13 feet (4 metres) total for the four footprints — suggesting it was walking at about 3.5 to 4.5 miles (5.6 to 7 kilometres) per hour, Lyson said. However, the number is way below its maximum speed, since preserved tracks were likely made in wet soil, and animals move fastest on firm dirt, explained Thomas Holtz Jr., a vertebrate paleontologist and principal lecturer in the department of geological, environmental and planetary sciences at the University of Maryland, College Park. He added that the footprints are still an important finding for paleontologists. “The most important aspect is that this is perhaps the first definitive Tyrannosaurus rex trackway sequence,” said Holtz, who was not involved in the study. The Denver Museum of Nature & Science plans to collect three prints from North Dakota to further analyze them for tissue and skin impression data, according to Lyson. The trackway’s publication gives other scientists the opportunity to analyze its measurements and reconstruct how the dinosaur moved, Romilio added. And knowing tracks like these exist could help researchers find more in the future, according to Holtz. By Taylor Nicioli, CNN
