Hip bone morphometrics of bottlenose dolphins (Tursiops truncatus) from Adriatic Sea: Sex determination and postnatal development

Bones are frequently the only cetacean samples available in the wild and may be useful for determination of sex, physical maturity, body length, and body mass. We analyzed the postnatal morphological development and morphometric characteristics of the cleaned and dried, paired hip bone (os coxae) from 131 bottlenose dolphins, Tursiops truncatus, (61 females, 70 males; total body length 117-322 cm) ranging in age from neonates to 28 yr, salvaged from Croatian waters of the eastern Adriatic Sea. Adult dolphins exhibited sexual dimorphism in their hip bone morphology and morphometrics: fully-formed hip bones from males were significantly longer, heavier, and more robust than those from females. Moreover, the fully formed hip bone from males featured a prominent bony tuberosity protruding dorsolaterally from the caudal half that was significantly wider and higher than in females. Morphometric measurements were used to generate classification functions for reliable sex determination (97%). In addition, hip bone length in both sexes correlated tightly with total body length, allowing one measurement to be calculated from the other. Only a single ossification developed in all hip bones although soft tissue attachments and comparative review suggests homological equivalence with the tripartite terrestrial mammal hip bone.