Flipper development in the Mediterranean striped dolphin (Stenella coeruleoalba).

Abstract

Studies of population biology are scarce in Mediterranean striped dolphins (Stenella coeruleoalba) mostly because of the lack of samples. Until now, studies of physical maturity, growth, and development of the flipper bones were not available for this species in the Mediterranean. The osteological features and metric characters of the pectoral limbs of Mediterranean striped dolphins were analyzed with radiological techniques. Measurements were made directly on the radiographic films. We found five carpal bones arranged in a proximal row of three and a distal row of two, although one or two additional osseous elements were occasionally observed. The phalangeal formula (excluding metacarpals) was established as 1-2:8-9-10:6-5-7:3-2:1-2. In metacarpals, epiphyseal ossification centers matured at the same time at both ends. As a general rule, the ossification of the epiphyses in the flipper bones showed a decreasing gradient in the proximodistal direction, confirming the pattern previously described in other species. Phalangeal epiphyses were not useful as indicators of skeletal maturity, and grading epiphyseal maturation of the distal radius and ulna is proposed as the more straight-forward and precise method for assessing bone maturation. In females, maturity of the flipper was achieved between 5 and 6 years of age and 160-175 cm of body length, whereas this maturation occurred between 8 and 9 years of age and 170-181 cm in length in males. Prediction of gender through examination of flipper structure was not feasible.