A TAXONOMIC AND TAPHONOMIC DESCRIPTION OF AN UNGULATE FOSSIL FROM THE CHADRON FORMATION OF THE BUFFALO GAP NATIONAL GRASSLANDS, SOUTH DAKOTA

In a recent field expedition to the Indian Creek area within the Buffalo Gap National Grassland, South Dakota, a field team from Wayland Baptist University collected fossil specimens from the White River Group. This area is recognized as one of the most fossiliferous localities spanning late Cretaceous to early Miocene strata. A partial mandible of a large fossil ungulate was recovered from the upper Chadron Formation and is being investigated for its taxonomic relationship and condition of preservation. A preliminary description and morphometric analysis has been conducted on recovered skeletal elements. The left dentary is highly fractured and measures 30.7 cm in length and 9.2 cm diagonally from the angular process to the curved antero-dorsal margin of the ramus, approximately 3 cm behind molar 2. Additionally, the left dentary contains an incomplete tooth row that measures 13.7 cm in length consisting of molars and premolars. The right dentary is represented by several bone and tooth fragments with an incomplete dentition while possessing enough material for a partial description. Based on dental and skeletal morphological comparisons to other large ungulates from the Chadron formation, Brontotheriidae and Hyracodontidae families are currently considered for taxonomic assignment. Most of the observed fractures in the left dentary appear to have occurred after fossilization. However, bone weathering and fracturing prior to fossilization is indicated by fracture-filling clay and flakes of bone within the matrix.