Bovid Origins

Recognition of the earliest fossil bovids is not straightforward, nor for that matter is recognition of early or stem members of the different bovid subclades. Bovidae is diagnosed by the presence of permanent and unbranched horn cores with a permanent and unbranched horn sheath (Janis and Scott 1988). Sheaths are rarely preserved as fossils, so the recognition of an early bovid in the fossil record relies on the presence and morphology of the bony horn core alone. This proposition is problematic, however, given that members of other pecoran groups also bear a very similar horn-core structure (both fossil and living species, e.g., Antilocapra americana) and given the potential absence of horns in female individuals. Dental and other cranial and postcranial osteological characters of potential use for distinguishing the earliest bovids and stem bovids should be further investigated. Teeth and cranial characters of certain species of Eotragus, long considered the earliest bovids, may indicate that certain of these species are basal to (i.e., precede on the cladogram) the last common ancestor of all the living Bovidae. Eotragus artenensis (Ginsburg and Heintz 1968; France, MN4 in Gentry et al. 1999; ca.18–17Ma in Steininger 1999) has been proposed as a stem bovid (see also Azanza and Morales 1994), as has E. noyei (ca.18Ma, Pakistan, Solounias et al. 1995). Eotragus minus, from the early Miocene of Pakistan, may be even older than E. noyei, and possibly more primitive in morphology (Ginsburg et al. 2001).

Other taxa worth further consideration in relation to stem bovids include Andegameryx, Amphimoschus, Namibiomeryx, Namacerus, Pseudoeotragus, and Homoiodorcas. Taxa included in Hypsodontinae (Köhler 1993) might be diphyletic to (i.e., the sister group of) the remainder of Bovidae (Gentry et al. 1999). Various Miocene taxa have been referred to Hypsodontinae (Köhler 1987). The group is in need of revision, having never been treated in much detail, and its phylogenetic status remains unclear.