Vertebral osteology in Delphinidae (Cetacea)

Vertebral anatomy in delphinid cetaceans exhibits marked heterogeneity. Description and functional interpretation of this variability is facilitated by the recognition of structural units along the column whose boundaries transgress those of the classical mammalian series. Vertebral anatomy of the killer whale (Orcinus orca) and the Atlantic white-sided dolphin (Lagenorhynchus acutus) lie near the ends of an anatomical continuum. Primitive columns resemble those of living delphinapterid delphinoids in exhibiting minimal intervertebral variation, low counts and spool-shaped vertebrae. Derived columns are more regionalized, displaying traits that limit mobility in the anterior torso, enhance flexibility at the point of neural spine syncliny and increase dorsoventral displacement of prefluke vertebrae. Reconstruction of the historical sequence of anatomical innovations identifies syncliny as an early and critical step in delphinid column evolution. Trait distribution supports evolutionary isolation of Pseudorca and Orcinus from remaining delphinids, inclusion of Feresa and Peponocephala among delphinine delphinids, and subdivision of delphinines on the basis of centrum dimensions, neural spine inclination and count. Details of vertebral anatomy can also be used to place fragmentary postcranial material, particularly that of fossils, in functional and evolutionary context. (C) 2004 The Linnean Society of London, Zoological Journal of the Linnean Society.