Survival of an Indian Ocean humpback dolphin Sousa plumbea in the wild despite chronic osteologic pathologies

Abstract

Skeletal examination of a female adult Indian Ocean humpback dolphin Sousa plumbea from South Africa suggested a chronic disease process. It manifested as erosions and pitting of the atlanto-occipital articulation as well as circumferential hyperostosis and ankylosis of some of the caudal vertebrae, findings rarely recorded together in the same animal. The character of the erosive process and vertebral fusion appeared chronic, and further findings of underdevelopment of the fluke, sternum and left humerus with remodeling of the periarticular region of the left scapula may support initiation of the process early in life. Because such chronic pathology would have affected the individual’s locomotion and foraging abilities, we also postulate how this individual survived until its demise in a human-derived environmental hazard. Ecological and socio-behavioral aspects observed in S. plumbea, including habitat preference for inshore and shallow waters, small social group aggregations and feeding cooperation, may have contributed to its ability to survive.