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Data for: Phylogenetic analyses reveal that horses deviate from a pervasive pattern of skull shape evolution

Wisniewski, Anna1; Slater, Graham2

Published Mar 26, 2026 on Dryad. https://doi.org/10.5061/dryad.crjdfn3g3

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Mar 26, 2026 version files 285.87 MB

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Abstract

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. In order to produce a phylogeny for comparative analyses we employed a meta-analytical approach, producing the first formally inferred species-level phylogeny for family Equidae.

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.