|NPS Paleontology Research Abstract Volume|
Arches National Park contains many sedimentary formations rich in fossil resources from the Late Paleozoic Era through the Mesozoic Era to the Quaternary Period. Of recent growing interest are its dinosaur tracksites. Tracksites are known within the Arches and Canyonlands region in the Chinle, Kayenta, Entrada and Morrison Formations. The majority of tracksites occur between the Entrada-Morrison contact.
Some of the sites have been known by local residents since 1940. An early ichnologist, Roland T. Bird surveyed a few of the sites after that time for possible inclusion into eastern museums. Research in the 1990s has been undertaken by Martin Lockley, Associate Professor of Geology at the University of Colorado and Director of the Dinosaur Trackers Research Group.
Originally, these tracks were believed to be part of the Moab Tongue member of the Entrada Sandstone. Evidence today suggest the tracks occur in the lowest member of the Morrison Formation of Late Jurassic age. The sediments represent a vast basin where the water table was at or near the surface (Lockley, 1991). The majority of tracks are of one type, a theropod that walked upright on two feet and left a three-toed impression. The track size ranges from several inches to over two feet. Claw marks are occasionally preserved.
The frequency of tracks ranges from one to several per square meter. Discoveries in the past six years have extended the tracksite boundaries to cover possibly hundreds of square kilometers. There may be from several million to over a billion tracks in the area occurring both within Arches National Park and outside the park on the surrounding Bureau of Land Management Lands (Lockley, 1991). Because of its extensive nature, it is referred to as a Megatracksite and is one of the few known in the country.
The full extent and significance of the Megatracksite is not known as many sections have not been completely inventoried, and additional sections have not been completely inventoried, and additional sections are discovered yearly. Currently, there is no special designation for the site and it is the present policy of the Bureau of Land Management and the National Park Service not to disclose the site to the general public.
An artifact constructed from a bison (Bison bison) hornsheath was recovered from the surface of a sandstone shelter also containing skeletal remains of bison and bighorn (Ovis canadensis). Radiocarbon dating of bison, bighorn, and the artifact indicate that all co-occurred on the central Colorado Plateau, southeastern Utah, either between A.D. 1405 and A.D. 1420, or between A.D. 1535 and A.D. 1605. Skeletal remains of the bison imply that the animal was of the local faunal community during the transition between Protohistoric and Historic time.
Great Basin Naturalist 51 (4), p.336-342, 1991.
|United States Department of the Interior, National Park Service|