A new fossil buffalo from the Shungura Formation (Ethiopia), and the role of size- shape allometry in the diversification of Syncerus

Allometry, the relationship between shape and size, plays a pivotal role in the diversification of phenotypes. The African buffalo, Syncerus caffer, the only surviving member of an extensive Pliocene-Pleistocene African bovin diversity, exhibits considerable morphological variability among extant populations. The extent to which size-shape allometry contributed to this variability, and potentially also to diversification of species of Syncerus, has remained unresolved due to limited fossil material. This study describes a nearly complete fossil cranium aged ~2.6 Ma from the Shungura Formation in southern Ethiopia, designated as the holotype of a new species. The new species, characterized by small size and short, divergent horns, shares similarities with populations of extant forest-dwelling Sy. caffer. Using 3D geometric morphometrics on fossil and extant bovins, we demonstrated that size-shape allometry accounts for a significant portion of cranial shape variation within Bovini, and that the new species is located close to small-sized and juvenile individuals of extant Sy. caffer. Our findings suggest that the newly described species represents an ancestral morphological template for the evolution of Syncerus, elucidating the mechanisms underlying the phenotypic diversification of African buffaloes. These results enhance our understanding of size-shape dynamics in bovin evolution and shed light on the early evolutionary history of Syncerus.