VERTEBRAL DEFORMITIES IN A SCHOOL SHARK, GALEORHINUS-GALEUS - CIRCUMSTANTIAL EVIDENCE FOR ENDOSKELETAL RESORPTION

The appearance of deformed vertebrae from a single mature female schoo l shark, Galeorhinus galeus, are described. Two unusual, pronounced bu mps were noticed in the caudal region of this shark. There were no sca rs in the skin over these protrusions, suggesting that the lesions had arisen internally. Radiographic and histologic investigation of these lesions showed that mineralized tissue had probably been lost followi ng an injury to the tail. Histological observations provided circumsta ntial evidence that mineralized tissue had been removed by internal pr ocesses, but did not reveal the agency by which skeletal tissue had be en resorbed. Since the capacity to resorb mineralized tissue is charac teristic of animals possessing bone, the apparent loss of mineralized tissue seen in this shark provides circumstantial evidence for the exi stence of bone cell lineages in school sharks. This evidence is discus sed in relation to the possible implications for evolutionary and fish eries biology.