On the systematic position of the oldest insular ruminant Sardomeryx oschiriensis (Mammalia, Ruminantia) and the early evolution of the Giraffomorpha

Sardomeryx oschiriensis is the oldest insular ruminant known (Burdigalian of Oschiri, Sardinia, Italy). Only two isolated upper dentitions compose the type material. The first phylogenetic hypothesis proposed Sardomeryx to be closely related to the Giraffoidea and especially the Late Miocene Sardinian derived giraffid Umbrotherium. Description of new specimens from Laerru (Burdigalian, Sardinia, Italy), including lower teeth and decidual premolars, leads to a reinterpretation of the phylogenetic position of Sardomeryx and of the early evolutionary history of the Giraffomorpha. Based on our phylogenetic hypothesis, Sardomeryx is nested within the Giraffomorpha as a basal Palaeomerycoidea. Sardomeryx may have originated from south-western Europe before the separation of the Corsica-Sardinia Block during the earliest Miocene. The enigmatic latest Oligocene Bedenomeryx from the south-west France is also considered as a basal (and the most ancient) member of the Palaeomerycoidea. Including Bedenomeryx in the Palaeomerycoidea lineage would place the origin of the Giraffoidea, the sister family of Palaeomerycoidea, within the Oligocene. Bedenomeryx is characteristic of arid south-western France, directly echoing the advanced condition observed in the Sardomeryx dentition (e.g. high crowned teeth, absence of the external postprotocristid on lower molar, reduction in length of the premolar row) typical for insular ruminants in arid environments.