A 2D geometric morphometric analysis of the occlusal enamel patterns of eastern Beringian equid cheek teeth, with taxonomic implications

Equids were among the most abundant land mammals of the Pleistocene and are well represented in the fossil record. However, the number of species that may have co-existed and their taxonomic nomenclature remain contentious. This lack of consensus is particularly acute in Beringia due to the limited number of studies conducted on equids from this region. Here, we use 2D geometric morphometric analysis to determine whether equids from eastern Beringia significantly differ in the shape of the occlusal enamel pattern for upper and lower premolars, and whether they form distinct morphotypes. Our results demonstrate that the analyzed aspects of the upper and lower occlusal enamel patterns of eastern Beringian equids are similar among the different morphotypes, particularly among those descended from the same lineage. Although occlusal enamel patterns can be used as a preliminary means of gaining taxonomic insights for eastern Beringian equids descended from different lineages, they should not be used in isolation. We suggest that future research aimed at resolving taxonomic uncertainties of Equidae should combine the use of dental characters with other methods of taxonomic identification. This work takes an important step towards disentangling the phylogenetic relationships of Beringian equids and resolving the debates surrounding their taxonomy.