Bathygenys Reevesi

myminifactory

Relatively few studies of cranial endocasts document intraspecific variation. Here, discrete morphological and morphometric variation from a sample of more than 150 natural cranial endocasts from a single Eocene locality, Reeves Bonebed (hereafter ‘RBB’) from West Texas are documented to provide clear understanding. The first detailed description of a digital endocast of an oreodont, Bathygenys reevesi is given to offer precise comparative data for other oreodont endocasts for better analysis. The RBB endocasts were initially assigned to B. reevesi, but nearly none have diagnostic craniodental material still attached, and isolated endocasts of other cetartiodactyl species are known from this locality. Consequently, an attempt was made to identify distinctive apomorphies on the RBB sample to diagnose specimens to the lowest possible taxonomic level with high accuracy. The RBB endocasts were diagnosed as oreodonts based on the presence of large, rounded casts of the tuberculum olfactorium, but no specimen can be definitively diagnosed to a particular species. The range for most linear measurements for the RBB sample overlaps with measures from multiple species of oreodonts from RBB. A coefficient of variation analysis of linear measurements suggests that the RBB sample represents more than one species. Therefore, endocasts from RBB that lack associated craniodental material cannot be definitively assigned to a species, and the original assumption that all are B. reevesi is not supported by evidence. This highlights the necessity of applying apomorphy-based identifications for isolated specimens, including endocasts, for accurate results. In addition, this study reveals some gaps in data from cetartiodactyl brains, which need to be filled for future studies on brain evolution in this clade to move forward with confidence.