Notes on the anatomy, positioning and homology of the pelvic bones in small cetaceans (Cetacea, Delphinidae, Pontoporiidae)

Abstract

This report analyzes the variations in positioning and orientation of the pelvic bones in small cetaceans, and contributes to establishing a possible homology based on the attachment of the abdominal musculature. Seven carcasses of three cetacean species (Tursiops truncatus, Sotalia guianensis, Pontoporia blainvillei) were analyzed. There is some variation in positioning and orientation of the pelvic bones in these species. Two pairs of abdominal muscles (levator ani and ischium-cavernosus) presented a tendinous connection to the pelvic bones in the species mentioned above, and the dorsolateral crest, the ventromedial protuberance and the ischial tuberosity occur in all analyzed species, thus constituting homologous structures. One can confirm at least the presence of the ischium as a component of the innominate bone of the cetacean.