Physical maturity of the vertebral column of Tursiops truncatus (Cetacea) from Southern Brazil

Abstract

Age, sex and total length are important variables for the analysis of ontogeny, sexual dimorphism and geographic variation among cetaceans. The physical maturity of cetaceans can be determined through analysis of the fusion of vertebral epiphyses. The animal is considered physically mature when all the epiphyses are fused to the vertebral body and the body growth ceases. The focus of the study is to determine physical maturity of the spine of Tursiops truncatus and compare with the age of individuals, which was obtained from the counting of Growth Layer Groups (G.L.G.). Twenty-four specimens were analyzed for the degree of epiphyseal fusion. As a result three vertebral maturation patterns were identified: Pattern 1 - vertebral column without fusion of epiphyses or fusion initiating only in cervical epiphyses (from zero to two years old); Pattern 2 - column with four degrees of fusion of epiphyses (from two to eleven/twelve years old); and Pattern 3 - column completely fused (more than eleven/twelve years old). For T. truncatus from the coast of Santa Catarina, southern Brazil, the fusion of vertebral epiphyses begins rapidly in the cervical region, followed by the caudal region, with the thoracic and lumbar vertebrae being the last to undergo fusion. Sexual dimorphism may be present during the maturation process of these animals, which became physically mature between eleven and fifteen years old. 

Key words: bottlenose dolphin, growth, vertebral epiphyses, age.