Skull morphometry and sexual dimorphism in the Kyrgyz horse: A multivariate size-corrected analysis

This study aimed to evaluate sexual dimorphism in Kyrgyz horse skulls by separating size and shape components using Mosimann log-shape ratios, based on 18 linear cranial measurements recorded from 39 specimens. Raw linear data were analyzed alongside size-corrected Mosimann log-shape ratios to distinguish overall size from size-independent shape. Males showed larger raw means than females for all 18 variables, and 14 measurements remained significant after false-discovery-rate correction. The strongest raw differences involved skull length to nasale, total skull length, nasal length, breadth between temporomandibular joint regions, and hard palate length. Geometric mean size was also significantly greater in males, confirming strong overall cranial size dimorphism. Multivariate analysis supported the same pattern: MANOVA showed a significant sex effect, and raw PCA was dominated by PC1, which explained 53.57% of variance and functioned as an overall size axis separating the sexes. In contrast, no size-corrected variable and no shape PCA score remained significant after FDR adjustment. Residual size-independent variation was concentrated mainly in diastema length, occipital squama height, foramen magnum dimensions, and nasal length, but these patterns were not strongly sex-structured. Correlation analysis further showed strong integration among rostrocaudal facial measurements and midfacial breadth variables. Overall, the findings indicate that sexual dimorphism in Kyrgyz horse skulls is pronounced in absolute size but weak in size-independent proportions, meaning that male skulls are largely scaled-up versions of female skulls rather than markedly different cranial shapes.