TAXONOMIC ASSIGNMENT OF TWO EOCENE ENTELODONT MANDIBLES FROM THE OGLALA NATIONAL GRASSLANDS

Two entelodont mandibles (TS-1-107-WC15 and TS-1-7-WC16) were collected from late Eocene strata in the Oglala National Grasslands of Nebraska. To identify taxon, the mandibles were prepared so that qualitative and quantitative analyses could be tested. Morphologically, entelodont mandibles exhibit significant variation. Furthermore, entelodonts are a diverse group making the description and identification of individual species difficult. In order to learn more about taxonomic relationships, the two mandibles were compared to museum specimens and known taxa recorded in the literature. TS-1-107-WC15 contains multiple post-fossilization fractures throughout the bone and is missing several teeth, but did manage to retain its first molar and canines. TS-1-7-WC16 was preserved relatively well, with most of its teeth and some of the ramus intact but did not retain its canines or incisors. To help with identification, length and width measurements of lower first molar was compared between TS-1-107-WC15 and TS-1-7-WC16. This data was then compared to the three most common species Archaeotherium mortoni, Archaeotherium wanlessi, and Archaeotherium latinden from the White River Group. When comparing the dimensions between length and width of the lower first molar, a linear relationship between the three Archaeotherium species is observed. The linear relationship has some overlap between the species, therefore a t-interval test was used to create confidence intervals (95%) in which specimens can be identified according to how they plot in comparison to the three species of Archaeotherium. TS-1-107-WC15 and TS-1-7-WC16 measurements of the lower first molar does not plot between the A. mortoni confidence interval, but does overlap with other A. mortoni data. This overlap occurs with data consisting of higher values for A. mortoni, and may indicate larger individuals. According to our quantitative analysis of lower first molar and qualitative characteristics, we propose TS-1-107-WC15 and TS-1-7-WC16 belongs to the species A. mortoni. Furthermore, this does compare favorably with the stratigraphic position TS-1-107-WC15 and TS-1-7-WC16 as A. mortoni is found exclusively in the Chadron Formation (late Eocene).