Researchers affiliated with the Denver Museum of Nature & Science and Liverpool John Moores University documented a four-print trackway in southwestern North Dakota that adds evidence about how an adult Tyrannosaurus rex moved. A connected sequence can reveal an animal's movement in ways an isolated footprint cannot, according to the study published online September 8 in the Journal of Vertebrate Paleontology.
Why researchers identify the trackmaker
The trackway was found in 2025 near Marmarth on U.S. Forest Service land. It extends about 23 feet and includes four three-toed footprints, each approximately 3 feet long. Researchers attributed the tracks to T. rex based on their size and shape, the age of the surrounding rock and the area's abundance of tyrannosaur bones, according to the journal paper and CBS News Minnesota.
Kent Hups, a high school teacher and amateur fossil hunter, discovered the trackway while volunteering on one of paleontologist Tyler Lyson's digs, as KMBC reported. Before the discovery, only two isolated adult T. rex footprints had been confirmed—one in New Mexico and one in Montana. Neither preserved a connected series showing the animal's progress.
A measured walking pace
The distance between the prints is about 13 feet. Biomechanical calculations place the animal's speed at roughly 1.5 to 2 meters per second, or about 3.5 to 4.5 miles per hour, consistent with a walking pace. Researchers estimated that the animal weighed more than seven tons, according to KMBC and the research paper.
The impressions survived as sandstone casts created when calcium carbonate cemented material around the original depressions. Later erosion removed softer rock around the hardened areas, leaving raised three-dimensional forms, according to the Tyrannosauripus entry and the research paper. Denver Museum researchers recorded the site with high-resolution 3D surface scanning, and lead author Peter Falkingham analyzed the digital data remotely, including in virtual reality, as described by Taylor & Francis Group.
Planned preservation work
Three of the four footprints are expected to be recovered by helicopter this fall and taken to the Denver Museum of Nature & Science. The move is a planned preservation step, not a transfer that has already occurred, according to Taylor & Francis Group.
What rules apply to fossils on Forest Service land?
According to the U.S. Forest Service's Dakota Prairie Grasslands, casual collecting without a permit is limited to reasonable amounts of common, non-commercial rocks, minerals and invertebrate or plant fossils; vertebrate fossils may not be collected. The Forest Service says museums and universities conducting more than casual fossil collecting on national forests and grasslands do so with permits, providing the legal context for research and institutional stewardship of discoveries such as this one. The Forest Service uses a Fossil Yield Potential Classification planning tool to assess geological units according to their likelihood of yielding paleontological resources that concern land managers. A North Dakota Department of Mineral Resources publication list also records a 2001 cooperative memorandum of understanding between the Geological Survey and the U.S. Forest Service's Dakota Prairie Grasslands to manage paleontological resources, documenting an earlier interagency stewardship effort in the region.
The surrounding badlands have also produced numerous tyrannosaur bones, including “Teen Rex,” a juvenile specimen found by three boys on a family hike in 2022. That local fossil record helped inform the researchers' assessment of the trackmaker, according to KMBC.
