Smithsonian.com

One of the Copper Ridge theropod tracks. The front of the foot - indicated by the three toe impressions - is towards the top of the picture. Photo by author.

Even when you know what to look for, dinosaur tracks can be easy to miss. I learned this the hard way on a recent visit to one small tracksite in eastern Utah.

Although Moab, Utah is best known for Arches National Park, uranium mines and various sorts of outdoor recreation, there are traces of dinosaurs in the area, too. Among the fossil sites is a short set of the only known sauropod tracks in Utah. About 23 miles north of Moab on State Road 191 is an inconspicuous, unmarked turnoff around mile marker 148.7. The unpaved road crosses a set of railroad tracks and disappears in the low, dusty hills, and after bumping along for about two miles in our small car, my wife and I arrived at the trailhead.

We spent about 15 minutes looking for the tracks. Neither of us could quite figure out where they were hiding, and the interpretive sign at the top of the trail gave no indication of where they might be. We had no idea that we had walked right over them until my wife spotted one of the large theropod tracks. Right at the top of the trail, there were at least three kinds of footprints set in the rippled, reddish rock, tracks that had persisted for about 150 million years. A fresh coating of dried mud gave some of the tracks a more recent look—as if the dinosaurs had walked by just last week—and partially obscured them from view.

The tracks were not all made at the same time. The sauropod footprints—attributed to Camarasaurus by the sign—were crossed by tracks left by a small theropod dinosaur moving in a different direction. The overlay of the smaller tracks meant that they were made after the big sauropod had passed. Footprints made by a larger predator were left just a few feet away. Several impressions recorded the movement of an Allosaurus-sized theropod, but the tracks had a curious pattern. Rather than indicating an even stride, the tracks alternated between long and short steps. Perhaps this individual had an injury that caused it to limp or take an irregular gait. Thanks to Allosaurus specimens like “Big Al,” we know that these dinosaurs did suffer foot injuries and infections that would have affected their ability to walk, and the Copper Ridge tracks might record the painful footsteps of one such dinosaur.