Unsupervised Wing-Bone Morphogroups in Bats Reveal Phylogenetic and Functional Patterns

Bat wings are complex biomechanical systems whose skeletal components play a central role in shaping flight performance. Although wing morphology in bats has traditionally been characterized using aerodynamic indices and ecological guilds, the contribution of individual wing bones to emergent patterns of wing design remains poorly understood. Here, we test whether interspecific variation in wing bone proportions is sufficient to generate objective, unsupervised morpho-wing bone groups (MWBGs) across Chiroptera. We quantified proportional variation in 10 wing bone elements relative to forearm length in 526 individuals representing 59 species from six bat families. Log-ratio-transformed measurements were analyzed using principal component analysis and hierarchical clustering, followed by linear discriminant analysis for group validation. We identified five robust MWBGs that explain coordinated variation in distal, intermediate, and proximal wing elements. These groups were recovered independently of a priori ecological classifications and showed higher discriminant performance than established foraging guilds. Phylogenetic mapping revealed that some MWBGs reflect strong phylogenetic conservatism (e.g., Molossidae), whereas others arise repeatedly across unrelated lineages, suggesting functional convergence in wing skeletal design. Distal phalanges and metacarpals emerged as key contributors to multivariate differentiation. Our results demonstrate that proportional variation in individual wing bones captures fundamental structural dimensions of bat wing morphology and provides a complementary, skeleton-centered framework for investigating the evolution of flight diversity in bats.