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