Scientists Find Fossilised Mammal Trackways at the Dinosaur National Monument

The United States National Parks Service established the Dinosaur National Monument in October 1915 following a presidential decree and in recognition of the scientific importance of the Jurassic sediments exposed in the state of Utah.  The fossils of a number of famous dinosaurs have been found in this area, dinosaurs such as Allosaurus, Apatosaurus and Stegosaurus.  However, a keen-eyed scientist has discovered that sharing this Jurassic environment with the huge dinosaurs were a number of tiny mammal species.  The ancient footprints and trackways of rat-sized creatures have been discovered at the Dinosaur National Monument site and these tracks provide a record of mammal activity from 190 million years ago.

Ancient Mammals

Commenting on the discovery, Dan Chure, a palaeontologist with the National Park Service stated that this was “an amazing find”.

It was Dan and his co-worker George Engelmann of the University of Nebraska who spotted the tiny footprints preserved on the side of a fossilised sand dune.  The two scientists hope that further examinations of the area may reveal fossilised skeletons of the tiny mammals.

The trackways, which number in the hundreds, were preserved in the Glen Canyon Formation.  This formation which consists of fossilised sand dunes that covered much of Utah and Wyoming as well as parts of Colorado, northern Arizona, and New Mexico during the Early Jurassic period has already provided a number of important dinosaur fossils.

Mr Chure stated that their discovery was a testament to the diversity of life in the arid region when the giant dunes, which reached heights of up to several hundred feet, were interrupted by an occasional oasis.

Fossilised Trackways

The tracks, discovered in the Utah section of the monument in Uintah County, indicate the little mammals were walking uphill because the heel imprints are more distinct than the toes.  The coin is provided for scale in the photographs.  Mammal tracks in this area are rare but they have been found before, unfortunately, tiny trace fossils such as these can be easily overlooked, the tracks themselves are only visible when light is shone on them from a particular angle.

“It was almost like a bunch of juveniles running around,” Chure said.

One of the challenges is accurately mapping the tracks, some of which are so faint they can only be seen when the light is at a certain angle.  Mixed up with the small mammal prints are the trackways of other animals, the scientists have tentatively ascribed these tracks as to belonging to small dinosaurs.

George Engelmann commentated:

“This was a time when the ancestors of modern mammals were losing dominance on land to the dinosaurs.  It’s near the beginning of a long time when dinosaurs ruled and our ancestors tried to stay out of their way”.

Such finds enable scientists to understand more about the food chains and eco-systems in ancient environments, helping them to build up a picture of life in the state of Utah 190 million years ago.

For models of prehistoric mammals: Prehistoric Mammal Models from Everything Dinosaur.