Metric variation in Afromeryx And Libycosaurus (Anthracotheriidae: Mammalia) and its utility for biochronology

Abstract

In mammal groups with few genera at any one time, such as the Neogene anthracotheres of Africa, not only can dental data yield evidence of geological age, but so can postcranial evidence. In the case of Late Neogene suids, which comprised several contemporaneous genera, dental data is useful for biochronology, but only when morphological and metric data are combined. In such groups, postcranial evidence is not as valuable because it is difficult to determine with confidence to which group such bones belong.

In Africa, in contrast, anthracotheres had low diversity throughout the Neogene, with usually three or fewer taxa present at most levels older than 17.5 Ma, and only one after ca 16 Ma to the end of the Late Miocene. Evidence shows that this lineage increased in size throughout its existence.

The aim of this contribution is to re-examine the question of variability in the Chad sample of Libycosaurus and to compare it to collections from other African localities in order to determine whether the size differences observed are compatible with a single species (Lebatard et al., 2008) or whether they support the presence of two species in the region (Pickford, 2008a, 2008b). If two taxa occur at Toros-Menalla, then this would have implications for the biochronology of the deposits (Pickford, 2008a, 2008b) whereas if only one highly sexually dimorphic species is present, it would have implications for understanding the ecology of these anthracotheres.