The stratigraphic importance of the brontothere (cf. Diplacodon elatus) in the Brennan Basin Member of the Duchesne River Formation of Utah

Abstract. We report on the first occurrence of an early horned brontothere in the Brennan Basin Member of the Duchesne River Formation in northeastern Utah. This is the first record of a brontothere from the Brennan Basin Member. Previously, brontotheres have been reported from the higher stratigraphic La Point Member (Duchesneodus uintensis) and the lower stratigraphic Uinta Formation (Sphenocoelus uintensis, Fossendorhinus diploconus, Metarhinus fluviatilis, Metarhinus abbotti, Sthenodectes incisivum, Metatelmatherium ultimum, Protitanotherium emarginatum, Pollyosbornia altidens, Diplacodon elatus). The recovered specimen consists of an upper third molar, which is comparable to the species Diplacodon elatus. The specimen supports the continued presence of brontotheres throughout the deposition of the Duchesne River Formation across the late Uintan to early Duchesnean North American Land Mammal Age. The previous lack of brontotheres within the lower beds of the Duchesne River Formation is likely a result of poor sampling and the relative rarity of fossils from this unit.