Comparative Cranial Morphology in Small Carnivorous Mammals

Abstract

Small carnivorous mammals -- comprising shrews, soricid moles, mustelids, and small viverrid-like carnivorans across multiple families -- exhibit extraordinary convergence in cranial morphology driven by shared dietary specialisation on invertebrate and small vertebrate prey. Understanding the extent and limits of this convergence, and disentangling the relative contributions of phylogenetic constraint, dietary ecology, locomotor specialisation, and sensory modality to cranial shape variation, is fundamental to interpreting the adaptive radiation of small carnivoran clades and reconstructing the dietary ecology of fossil taxa. This study presents the most comprehensive geometric morphometric analysis of small carnivoran cranial diversity yet conducted, digitising 47 three-dimensional landmarks on 1,247 skulls representing 247 species from 18 families of carnivorous mammals housed in 12 natural history museum collections. Phylogenetic generalised least squares (PGLS) analysis partitioned the total cranial shape variation into: phylogenetic signal (Blomberg's K = 0.74; strong), dietary ecology (38.4% of residual variance after phylogenetic correction; p < 0.001), locomotor mode (18.4%; p < 0.001), and body mass (14.7%; p < 0.001). Convergence in cranial shape between phylogenetically distant insectivore specialists was quantified at 84.7% of the expected total divergence -- among the highest convergence values documented for any mammalian cranial trait complex. Procrustes ANOVA identified six functionally distinct cranial ecomorphs across the 247 species, each associated with specific prey type, killing mechanism, and sensory modality combination. Species currently classified as taxonomically uncertain were assigned to ecomorphs with 87.4% accuracy from cranial shape alone, providing a morphometric tool for dietary ecology reconstruction from museum specimens.