RECONSTRUCTION OF THE PALEOCENE ECOSYSTEM OF THE MEDORA SITE, BILLINGS COUNTY, NORTH DAKOTA, USING MICROFOSSILS

Over the last two decades, fossils have been collected from the Medora Site (NDGS L78), located near the town of Medora, Billings County, North Dakota on Theodore Roosevelt Medora Foundation property, by the North Dakota Geological Survey and volunteers. The Medora Site preserves fossils within the Paleocene (60 million year old) Sentinel Butte Formation. Screen washing matrix from the site has yielded thousands of microfossils representing a diverse invertebrate and vertebrate fauna.

Over 2500 fossil elements have been extracted and identified. The site includes an abundance of fishes, including Amiidae, Lepisosteidae, and Teleostei taxa, with bowfins and teleosts being most abundant. Fish specimens include scales, vertebrate, ribs, and plentiful teeth.

Other vertebrates are also well represented at the site, particularly amphibians and reptiles. Turtle carapace and plastron fragments have been recovered along with salamander elements. The most commonly found reptiles at the site are champsosaurs and crocodiles. Numerous champsosaur and crocodilian teeth were recovered, along with a small number of skeletal elements. The larger teeth measured between 15 and 20 mm in length. Mammalian teeth and jaws, as well as Aves elements, are sparsely preserved, but confirm their presence at the site.

Molluscan specimens and plant material help to round out the picture of this ecosystem. The fossil data allow for insights into the ecology of western North Dakota following the end-Cretaceous extinction. The diversity of taxa supports the reconstruction of the Medora Site as a fresh water aquatic ecosystem.