An enigmatic giraffid from the latest Miocene of Italy: Taxonomy, affinity, and paleobiogeographic implications

The origin and evolution of endemic species characterizing the Oreopithecus-faunal assemblages of the Tusco-Sardinian archipelago remain a matter of debate. An emblematic case is the enigmatic giraffid Umbrotherium azzarolii, represented by a single specimen from the type locality of Casteani (Tuscany) and by several isolated teeth and fragmentary mandibles from the locality of Fiume Santo (Sardinia). An exhaustive diagnosis of Umbrotherium has not been firmly established, and its systematic and phylogenetic position remain unresolved. Unpublished remains of giraffids, including an almost complete mandible, several isolated teeth, and other cranial remains are described for the first time in the present work. The specimens were collected from the locality of Botro della Canonica (Pisa), located at the northernmost portion of the Tusco-Sardinian archipelago. The new material sheds light on the morphological and morphometric variability of Umbrotherium, thereby enabling a comparison between specimens collected from different Tusco-Sardinian Miocene localities spanning from the V1 to the V2 Oreopithecus-Zone Faunas and allowing the establishment of the new species U. engesserii sp. nov. from Fiume Santo (Sardinia). This study also reveals that Umbrotherium was more closely related to Decennatherium than to other Late Miocene continental giraffids, suggesting a dispersal of its ancestor from the Iberian Peninsula. Accordingly, a new paleogeographic and biochronological framework is proposed herein for the Tusco-Sardinian archipelago, hypothesizing a fragmentation of the area into several domains, with sporadic reconnections, and the establishment of different faunal assemblages.