A thorny taxonomic issue of Quaternary deer (Cervidae: Mammalia) from the South American Highlands resolved based on the recognition of a paleopathology

The diversity of South American deer genera during the Quaternary is considered one of the greatest in the world. However, this was established during the beginning of the twentieth century, when the recognition of new extinct deer taxa was based only on differences in antler morphology. Thus, South American extinct deer taxa need a detailed taxonomic revision, and this is the case of the Andean deer genera Agalmaceros and Charitoceros. First, both taxa are diagnosed by the presence of thorns in their antlers. Consequently, by taxonomic priority, Agalmaceros is a senior synonym of Charitoceros. Second, we recognize here that the thorns of the antlers of Agalmaceros are the symptom of a pathology that also affects some extant deer. Excluding the thorns of the antlers, the antler of Agalmaceros is identical to that of Odocoileus virginianus, indicating that Agalmaceros is a junior synonym to this extant deer. The recognition of epizootic hemorrhagic disease as the possible cause for the thorny antlers of Andean O. virginianus and the ample record of this affecting antlers in deer from the tropical Andes suggests that an epidemic occurred in this region in the Late Pleistocene. Before describing a new taxon, taxonomists must exhaust all possibilities to explain morphological variations. In this regard, this contribution provides an interesting, important and weakly explored area in paleontology, namely taxonomic revision under a paleopathology context. With the taxonomic invalidation of Agalmaceros and Charitoceros proposed here, the diversity of South American deer genera during the Pleistocene is poorer than previously established and includes 11 taxa – seven extant and four extinct.