2026/06/15 by Anna L. Wisniewski, Graham J. Slater
Mathematics · Earth and Planetary Sciences · Social Sciences · #Morphological variations and asymmetry #Evolution and Paleontology Studies #Pleistocene-Era Hominins and Archaeology
paper · pdf · doi:10.1017/pab.2026.10096
Abstract The mammalian skull plays important roles in sensing, communication, and obtaining and processing food. These diverse functions make the skull a natural target for investigating how developmental processes and selective pressures related to ecology interact to produce patterns of morphological evolution. Here, we investigate the evolution of the equid skull through the lens of craniofacial evolutionary allometry (CREA), a pattern of relative facial elongation in larger mammals that has been hypothesized to result from similar patterns of facial elongation over ontogeny. Using 3D geometric morphometrics and linear measurements, we describe the major axes of shape variation in the equid skull, test whether equids follow or deviate from the CREA pattern over the clade’s evolutionary history, and assess whether the evolution of high-crowned teeth (hypsodonty) is related to relative facial proportions, all in an explicitly phylogenetic context. We find that equids deviate from the CREA pattern and that the evolution of hypsodont dentition did not significantly influence facial proportions in the group. Importantly, these results are only apparent when using statistics appropriate for phylogenetic data. Comparison with previously published data on facial proportions from modern equids indicates that ontogenetic patterns of facial elongation do not scale to produce patterns of facial proportions observed at the intraspecific and evolutionary levels. Taken together, our results complicate the historic narrative that a single set of selective factors drove patterns of morphological evolution within the group.