A new fossil buffalo from the Shungura Formation (Ethiopia) reveals the role of heterochrony in the evolution of Syncerus

Variation in the timing and rate of development (heterochrony) is a key driver of morphologicaldiversification. The African buffalo (Syncerus caffer) is the sole surviving species of a oncediverse Pleistocene lineage and shows striking eco-morphological variability that may be theresult of heterochronic shifts. Heterochrony has also been suspected to account for the pastdiversity of Syncerus, but the early evolution of this clade has remained obscure due to limitedfossil evidence. Here we describe new material from the Shungura Formation (southernEthiopia), including a nearly complete cranium dated to ~2.6 Ma, which we designate as thetype of a new species of Syncerus. This species is small-bodied with short, divergent horns,resembling immature and small-bodied extant Sy. caffer (forest or ‘nanus’ ecomorphs). Three-dimensional geometric morphometrics reveal that fossils of Ugandax and Syncerus (includingthe new cranium) broadly follow the ontogenetic size-shape allometry of Sy. caffer, suggestingcranial diversification along a conserved allometric trajectory, and that the new species mayrepresent an ancestral form from which later Syncerus evolved. In contrast, the extreme hornlength of the extinct giant buffalo Sy. antiquus departs from this pattern, indicating lineage-specific innovation. These findings provide the earliest well-preserved evidence of the Africanbuffalo lineage and highlight the role of conserved allometry and heterochrony in theevolutionary history of Syncerus. They also underscore the importance of new fossildiscoveries and comparative analyses for understanding the origins of morphological diversity.