Paleontology owns thousands of Tyrannosaurus rex bones, dozens of skeletons, and exactly one thing it never had until this week: a recorded walk.

In a study just published in the Journal of Vertebrate Paleontology, researchers from the Denver Museum of Nature & Science and Liverpool John Moores University describe the first trackway ever attributed to an adult T. rex — four enormous three-toed footprints in sequence, two left and two right, pressed into what was Hell Creek mud about 66.5 million years ago, in the species’ final act before the asteroid.

Bones are anatomy. A trackway is behavior — a preserved moment of an animal actually doing something. “With a trackway, we can actually follow an animal as it moved across the landscape,” said Denver’s senior curator Tyler Lyson. “That is incredibly rare for T. rex.”

Reading the walk

The trackway, found in 2025 on U.S. Forest Service land near Marmarth, in North Dakota’s fossil-rich southwest corner, runs about 23 feet, with each print roughly three feet long and a stride — the gap between successive prints of the same foot — of approximately 13 feet.

Feed the stride and footprint size into the standard locomotion equations and out comes the headline number: the animal was moving at about 3.5 to 4.5 mph — the pace of a brisk human walk. Seven tons of apex predator, out for a stroll. The team is careful to call the figure approximate, since the prints are heavily weathered — but the pace sits comfortably alongside other large theropod trackways and the biomechanical consensus that a walking T. rex preferred exactly this kind of unhurried gait.

The attribution rests on elimination. Tyrannosaur trackways found before — in Canada, in Wyoming — were left by smaller animals: juveniles, or smaller related species. These prints’ sheer size, the narrow angle between the toe impressions, and the surrounding rock’s abundance of adult T. rex bones leave no other known animal in the formation matching the feet. Isolated single prints had been credited to adult rex before; a walking sequence — the thing that yields a stride, and therefore a speed — never.

The expert who never saw the tracks

The project’s methods are as modern as its subject is ancient. The prints survive in an unusual medium — hardened, calcium-carbonate-cemented sandstone casts, natural sculptures of the original squelch — and the field team documented every print with high-resolution 3D surface scanning.

Which enabled the study’s charming structural joke: lead author Peter Falkingham, one of the world’s foremost dinosaur-track experts, analyzed the trackway without ever seeing it in person — colleagues scanned the stones in the North Dakota badlands and sent him the models in Liverpool. The find itself, by the accounts circulating with the study, was first spotted not by a professional at all but by a high-school teacher working with the museum’s field program — hikers and amateurs being, as track specialists have long noted, the discipline’s best discovery engine.

Three of the four prints are due to be airlifted out by helicopter this fall and installed at the Denver Museum.

Why a slow walk is big news

There is a mild comedy in the fact that the most fearsome animal ever to walk North America makes headlines for ambling — but the pedestrian pace is precisely the scientific payload.

How T. rex moved has been fought over for decades: the Jurassic Park jeep-chaser versus the biomechanical models showing that a running rex would have needed impossible quantities of leg muscle, with modern estimates converging on a fast-walking animal whose long legs made walking efficient rather than swift. Those conclusions, though, were built from bones, models and other species’ tracks. This is the first time the actual animal has weighed in — an adult rex, caught mid-commute, moving at exactly the relaxed pace the equations predicted. One data point, and an unhurried one, but from the only witness that was there.

And that is the real gift of the Marmarth stones. Every skeleton is a death; a trackway is twenty-three feet of a Tuesday. Sixty-six and a half million years ago, in the last few hundred millennia of its species’ existence, a full-grown Tyrannosaurus rex walked across a mudflat at the speed of a human late for lunch, going about business no one will ever know — and the mud kept the receipt.