Scientists at Utah's Dinosaur National Monument have been quite busy this summer. At the beginning of the season they were blasting some sauropod skulls out of the rock for collection, and now the Chicago Tribune reports that they have discovered hundreds of tiny footprints in rock about 190 million years old. These tracks were not made by dinosaurs, though, but possibly by mammals.
Even though many people think of the Mesozoic (about 251 to 65 million years ago) as the "Age of Dinosaurs," there were plenty of other creatures around during that time. The first true mammals evolved around 190 million years ago, about when the Dinosaur National Monument tracks were made, although mammal-like creatures had been around for tens of millions of years. Once the first mammals evolved, the group began to diversify, giving rise to the ancestors of modern groups as well as lineages that have gone extinct.
According to a Chicago Tribune report, it seems that the creatures that made the tracks lived in a dry, desert-like environment. Each dime-sized track differs in preservation, but together they provide a snapshot into the life of a rat-sized creature scurrying about the ancient dunes. Given that the animal did not die in its tracks, however, we cannot be entirely sure whether the tracks were made by a "true" mammal or a creature closely related to the common ancestor of all mammals. Since the details used to tell the difference between mammals and mammal-like animals are skeletal, it may not be possible to determine which sort of animal made the tracks. Still, though, the tracks are a rare find and I cannot wait until they are published in an academic journal so we can all learn more about them.