A Giant Carcass Initially Reported as a Whale is a Basking Shark － Evidences of Vertebral Histology

Abstract

A large bleached carcass, 3.5m in length, stranded on the beach of Izumozaki, Niigata District, Sea of Japan, and first reported by local press as a kind of whale, was identified as a basking shark, Cetorhinus maximus, following examination of the vertebrae. Two vertebrae, 169 and 135mm in diameter, were biconcave (double cone) colums, each being equipped with 3 concavities receiving a basidorsal neural arch and two basiventral hemal arches. The cartilaginous vertebra was classified as having a type of cyclospondylous centrum, consisting entirely of numerous pieces of porous lamellae. Under light microscopy, a marginal flange corresponding to the diaphysis (substantia compacta) was seen to be composed of fibrous sheets, while the radiating lamellae, corresponding to the epiphysis (substantia spongiosa), showed a meshwork architecture. Scanning electron microscopy revealed that the flange was an aggregation of rough rods with a considerable number of fibrous connective tissue strands. On the other hand, the porous lamellae formed an intricate cancellous texture.