Ontogeny of the skull of Sotalia guianensis (Cetartiodactyla: Delphinidae) on the Northern coast of Brazil

ABSTRACT This study aimed to investigate the ontogenetic development of the skull in the Guiana dolphin (Sotalia guianensis Van Bénéden, 1864 ) through the comparison of 29 morphological non-metrical characters together with the estimated age of 54 specimens derived from four areas on the northern coast of Brazil. The state of each character was associated with the age of each specimen to assess the formation of bone structures, and the degree of fusion of the sutures in each state of the character studied. Nineteen qualitative morphological characters presenting state ontogenetic variations have been analyzed statistically. The analysis depicted that the characters associated with the parietal-frontal suture, parietosupraoccipital, parietoexoccipital, supraoccipital-exoccipital and basioccipital-pterygoid varied according with the age. The results suggest that the physical maturity of the cranium was more premature in the specimens from the Northern Coast, suggesting a geographical adjustment of the species, or a biological response to an intense pressure of by-catch in fisheries over decades on the populations.