Vertebral Morphology in Dolphins (Delphinidae): A 3D Approach

Abstract

This is the first 3D geometric morphometric study of vertebral morphology in such a large and diverse group of dolphins (24species). The aim was to describe and compare vertebral shape within Delphinidae, and assess its relationship with the biomechanical demands of each species. Phylomorphospaces were used to visualize shape variation among closely related species with different habitats. Associations between vertebral shape and size, habitat, diving depth, and vertebral count were explored following dimensionality reduction. The torso and tailstock exhibited the greatest morphological variations. Shape variation was significantly associated with size, habitat, and vertebral count in specific regions, depending on the factor. The estimated ancestral shape suggests an oceanic habitat. Coastal and riverine taxa showed reduced vertebral count and shapes associated with greater flexibility, supporting the idea that these traits may have evolved secondarily within Delphinidae. The greatest modifications were observed for deep-diving and extremely fast-swimming species. Overall, these results support the hypothesis that diversification in vertebral morphology, linked to ecological specialization, may have contributed to the explosive radiation of delphinids. This work also provides a morphological baseline for future studies exploring phylogenetic constraints in delphinid evolution.