Bilateral Directional Asymmetry of the Appendicular Skeleton of the White-Beaked Dolphin (<I>Lagenorhynchus albirostris</I>)

Abstract

Bilateral directional asymmetry of the lengths and diameters of the scapula, humerus, radius, and ulna were analyzed on a sample of 38 white-beaked dolphins (Lagenorhynchus albirostris) from Danish waters. The levels of asymmetry were consistent between the sexes and between physically mature and immature animals. The length and diameter of the humerus and the length of the radius showed significant asymmetry, all favouring the right side. The greatest asymmetry was found in the diameter of the humerus (1.88% SE 0.36). The results were somewhat different from what is known in the harbour porpoise (Phocoena phocoena) that show asymmetry favouring the right side in all of the dimensions investigated here. This may indicate a different pattern of employment of the flippers. The detected asymmetries, along with the many examples of lateralized behaviour recorded in cetaceans, point to the existence of lateralized use of the flippers in the white-beaked dolphin and possibly other delphinid and cetacean species. Although some evidence exists for flipper preference in the baleen humpback whale (Megaptera novaengliae) and turning preferences in other species, this needs to be confirmed through further behavioural studies.