Ankylosis patterns in the postcranial skeleton and hyoid bones of the harbour porpoise (Phocoena phocoena) in the Baltic and North Sea

Abstract

The onset and timing of epiphyseal ankylosis in the vertebral column and flippers and ankylosis of the hyoid and sternal bones were studied in 350 skeletons of the harbour porpoise (Phocoena phocoena) originating from the Baltic and North Sea and held in the collections of the Zoological Museum (University of Copenhagen), the Museum of Natural History (Gothenburg), the National Museum of Natural History (Stockholm), and the German Oceanographic Museum (Stralsund). Epiphyseal ankylosis in the vertebral column started in the anterior cervical region and then initiated around the 23rd to 26th caudal vertebrae from where it proceeded in both directions. The progression of vertebral epiphyseal ankylosis eventually terminated in the thoracic and lumbar regions. Epiphyseal ankylosis in the flippers began at the distal end of the humerus and the proximal ends of the radius and ulna. The timing of ankylosis in the flippers was more consistent across the specimens than the timing of vertebral ankylosis. Males and females had similar timing of ankylosis in the vertebral column and the flippers. Complete fusion of the hyoid and sternal bones occurred within the first year of life in most specimens. The early development of the hyoid apparatus may be linked to use of suction in feeding.