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A Protoceratops skeleton with an associated track (outlined in a box near the hips). From Niedźwiedzki et al., 2011.

Earlier this week I wrote about a herd of small sauropods that once walked along the edge of a shallow bay in Cretaceous Spain. Just what species these dinosaurs belonged to could not be determined—matching tracks to trackmakers is a tricky business. Every now and then, though, paleontologists uncover tracks associated with the creature that created them. Fossil invertebrates, such as trilobites, are sometimes found next to their tracks and burrows, and now paleontologists Grzegorz Niedźwiedzki, Tomasz Singer, Gerard Gierliński and Martin Lockley report that the remains of a small horned dinosaur can be matched up with a track found associated with an articulated skeleton.

The fossils, which form the basis of a paper that will appear in Cretaceous Research, were collected more than 45 years ago during the Polish-Mongolian Expedition to the Gobi Desert. The dinosaur, which lived sometime between 84 million and 75 million years ago, is a small horned dinosaur common to the area, called Protoceratops. What is remarkable about this specimen, though, is that preparators working on the fossil found a four-toed footprint underneath the petrified pelvis of the dinosaur. Such close association between tracks and their potential trackmakers is extremely rare—the first line of the paper reads: “Finding a dinosaur dead in its tracks constitutes the holy grail of vertebrate ichnology.”

But association isn’t everything. The footprint has to fit the foot of the dinosaur it is associated with. (The need for this correspondence has previously led one of the paper’s authors, Martin Lockley, to call the search for the foot which fits the right footprint “the Cinderella Syndrome.”) In this case, the bones and the track fit well. The track was not left by some other kind of dinosaur—it’s not a ankylosaur track or raptor track—and it closely accords with the left foot of the Protoceratops.

There is one little twist to the story, though—the animal found associated with the footprint may not have actually left the track it was buried with. According to the authors of the paper, the track indicates that the animal was in active motion when the track was left. If this is correct, then it is strange that the footprint and skeleton are so close together, as if the dinosaur keeled over right after taking that last step. The track was not made by the foot of the animal after its death, and may not represent the last steps of the individual represented by the skeleton. Another protoceratopsid dinosaur may have walked by at an earlier time, in the place where a different individual of the same species later died. Given the state of the evidence it is impossible to tell which scenario is correct, but in either case, the track was almost certainly left by Protoceratops. Hey, if the footprint fits…

References:

Niedźwiedzki, G., Singer, T., Gierliński, G., & Lockley, M. (2011). A protoceratopsid skeleton with an associated track from the Upper Cretaceous of Mongolia Cretaceous Research DOI: 10.1016/j.cretres.2011.07.001