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

  1. Faysal Bibi
  2. Jean-Renaud Boisserie

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Abstract

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.

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  1. Peer Community in Paleontology

    The evolution of the mammalian herbivore skull has long been a treasure trove in search for the processes behind the diversity of mammalian cranial adaptation. Artiodactyl (even-toed ungulates) have a particularly prominent position in this area, having produced several diverse radiations with often extensive fossil records linking their ecology and evolution (Janis, 2007). They have particularly been the subject of studies trying to discern how development and adaptation can work together to produce their cranial diversity, with the added bonus of their highly diverse horns and antlers that have been a staple for studies of heterochrony-driven evolution (McNamara, 2012). 

    The paper by Bibi and Boisserie (2025) adds a deep-time and extended developmental perspective on previous finds including the lead author (Bibi and Tyler, 2022) that bovid artiodactyls (antelopes, cattle, sheeps/goats, and relatives) display strong cranio-facial allometry (changes of shape with size), where larger species have longer faces than smaller ones. The present study describes a new fossil of the morphologically diverse buffalo genus Syncerus, represented today only by the morphologically highly diverse African buffalo species Syncerus caffer. Adding this unusually small and ancient species to superb existing extant and fossil data, using geometric morphometrics of the cranium and linear morphometrics of the horns, allows the authors to ask how buffalo cranial diversification could have been driven by allometry and heterochrony (differences in rate and timing). 

    The results overall confirm a common pattern of craniofacial allometry in the data including buffaloes and other bovines, where larger species have longer faces. This is consistent with the concept that biomechanical trade-offs allow larger species more gracile skulls when the mechanical properties of food remain unchanged (Mitchell et al., 2024). However, there is an interesting twist that allometric trajectories within the Syncerus genus (as well as other bovine genera) is potentially the opposite (with larger body masses coinciding with shorter faces). The study also makes the exciting find that horn shape and proportions are far less allometric than cranial shape and a major contributor to cranial diversification away from a common allometric trajectory among bovids. 

    I find the paper exciting because it took the rare opportunity to integrate excellent fossil data in an ideal artiodactyl system, allowing co-analysis of deep-time evolutionary patterns and integration of Evo-Devo. Aside from the important insights on the origin and diversification of the Syncerus genus, what really stands out to me is the cranium versus horn dichotomy. To me, this is a great example of how the cranium is not a homogenous entity and shape variation patterns will vary depending on the kind of selection acting on them (Marcy et al., 2024). It is also fascinating how larger-scale patterns appear to not apply at shorter time scales, showing how important datasets like these with good coverage of evolutionary divergences are. I hope that more fossils will be found that can provide more insights into this fascinating genus, but this thought-provoking and meticulously analysed study is a fantastic base with implications far beyond the taxonomic system it investigates.

    References

    Bibi, F., and Boisserie, J.-R. (2025). A new fossil buffalo from the Shungura Formation (Ethiopia) reveals the role of heterochrony in the evolution of Syncerus. PaleorXiv, eh9s8, ver. 5, peer-reviewed by PCI Paleo. https://doi.org/10.31233/osf.io/eh9s8_v5

    Bibi, F., and Tyler, J. (2022). Evolution of the bovid cranium: Morphological diversification under allometric constraint. Communications Biology, 5(1), 69. https://doi.org/10.1038/s42003-021-02877-6

    Janis, C. M. (2007). Artiodactyl paleoecology and evolutionary trends. In D. R. Prothero and S. E. Foss (Eds.), The Evolution of Artiodactyls (pp. 292–302). Johns Hopkins University Press, Baltimore. https://doi.org/10.56021/9780801887352

    Marcy, A. E., Mitchell, D. R., Guillerme, T., Phillips, M. J., and Weisbecker, V. (2024). Beyond CREA: Evolutionary patterns of non‐allometric shape variation and divergence in a highly allometric clade of murine rodents. Ecology and Evolution, 14(7), e11588. https://doi.org/10.1002/ece3.11588

    McNamara, K. J. (2012). Heterochrony: The evolution of development. Evolution: Education and Outreach, 5(2), 203–218. https://doi.org/10.1007/s12052-012-0420-3

    Mitchell, D. R., Sherratt, E., and Weisbecker, V. (2024). Facing the facts: Adaptive trade‐offs along body size ranges determine mammalian craniofacial scaling. Biological Reviews, 99(2), 496–524. https://doi.org/10.1111/brv.13032

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