The tracks are embedded in a layer of rock known as the Middle Jurassic Bajocian Gypsum Spring Formation, a 165- to 167-million-year-old rock formation that contains fossilized remains of a marine shoreline and tidal flats. Geologists believe an inland sea, called the Sundance Sea, covered Wyoming, Colorado and a large area of the western United States during the Jurassic period from about 165 million years ago to 157 million years ago.
Debra Mickelson of CU-Boulder’s geological sciences department said the research team identified the tracks of the six-foot-tall, bipedal dinosaur at a number of sites in northern Wyoming, including the Bighorn Canyon National Recreation Area. “It was about the size of an ostrich, and it was a meat-eater,” she said. “The tracks suggest it waded along the shoreline and swam offshore, perhaps to feed on fish or carrion.”
The dinosaur does not have a name, although Mickelson is continuing to look for bones and other remains that could be used to identify and name the new species. “This dinosaur is similar to a Coelosaur,” she said. “It is a dinosaur with bird-like characteristics and is a possible ancestor of birds. It lived in a much earlier time period and was very different from larger dinosaurs like T-Rex or Allosaurus.”
The tracks are of different sizes and were deposited at about the same time, according to Mickelson, revealing that the dinosaurs likely traveled in packs and exhibited some variation in overall size. “Further research into the geologic record and depositional history of the region supports our conclusion that the dinosaurs were intentionally swimming out to sea, perhaps to feed,” she said.