Growth and skull development in the South American fur seal, Arctocephalus australis (Zimmermann, 1783) (Carnivora: Otariidae), from Rio Grande do Sul coast, Brazil.

Abstract

Skulls of 157 Arctocephalus australis (94 males and 63 females) from animals stranded dead on the Rio Grande do Sul coast from Torres to Barra do Arroio Chuí between July 1977 and September 1997 were examined. These were analyzed to explore aspects of the cranial development. The growth layers groups (GLGs) in the dentine and cementum from upper canine teeth were counted. The oldest male and female were 14 and 18 years of age, respectively. Parameters of the von Bertalanffy equation suggest that males and females attain physical maturity at about the eight and six years of age, respectively. Hotelling T² test and discriminant functions using metric characters showed sexual dimorphism in physically mature and immatures skulls. The developmental classes were also examined using non-metric characters, but no sexual dimorphism was observed using these variables. The principal component analysis (PCA) showed a clear separation between physically mature skulls of males and females. The first factor explained 80.2% of the total variation and the second factor explained 4.6% of the observed variability.