He looked closer. The shape was a footprint with three toes, nearly a metre long. Hups teaches science at Northglenn High School in Colorado and is a research associate with the Denver Museum of Nature & Science. He took out his phone and texted the expedition's leader, the paleontologist Tyler Lyson: "Hey just found a t Rex footprint!!!!!"
The team kept digging and found three more prints, two left feet and two right, in a line about 7 metres long. From one print to the next print of the same foot the stride measures about 4 metres. From that stride the researchers worked out how fast the animal was moving: 5.6 to 7.2 km/h, close to a brisk human walk. The rock that holds the prints is about 66.5 million years old, from the last stretch of time before the dinosaurs disappeared.
Before this, only two isolated adult T. rex footprints had ever been identified. The geologist Chuck Pillmore found one in 1983 at Philmont Scout Ranch in New Mexico. The other came from the same Hell Creek Formation, in Carter County, Montana. None of those earlier finds showed the animal taking more than one step.
The paper describing the trackway appeared in the Journal of Vertebrate Paleontology. Its lead author is Peter Falkingham, a professor of palaeobiology at Liverpool John Moores University. In 2008 he co-wrote the paper on the Montana track, so he has now helped describe two of the three known finds. Co-author Evan Tamez-Galvan made high-resolution 3D scans of the surface so the prints could be studied as digital models.
The authors are careful about what they claim. The paper's title calls the trackway only "likely attributable" to an adult T. rex. They point to three pieces of evidence: the size of the prints, the narrow shape of the toes, and the large number of T. rex bones already found in the surrounding rock. The same area near Marmarth produced "Teen Rex", a juvenile skeleton found in 2022 by three children.
The site is on federal land managed by the U.S. Forest Service. This autumn, three of the four prints are due to be lifted out by helicopter and shipped to the museum in Denver for further study. The museum plans to share news of the recovery with visitors over the winter.
Hups had been looking for the easiest way up the hill. What he found was a record of an animal walking through the same country 66 million years earlier.