Size and shape variability in the skull of Pontoporia blainvillei (Cetacea: Pontoporiidae) from the Brazilian coast

A. Higa, E. Hingst-Zaher, M. Vivo


The existence of sexual dimorphism in Pontoporia blainvillei has long been known, with females being larger than males. However, no study so far has explored this dimorphism separately in its size and shape components. Here we analyse sexual dimorphism present in eight linear measurements of the skulls of 56 specimens (30 females and 26 males) of P. blainvillei from several localities along the Brazilian coast. We also investigate the sexual dimorphism in size and shape using geometric morphometric techniques, employing a subsample of the specimens above consisting of 27 skulls (12 females and 15 males). The analysis was based on landmarks digitized in four views of the skull: dorsal, ventral, lateral and occipital. A PCA showed the existence of two distinct populations, thus requiring the separation of two samples for the analysis of the effects of sexual dimorphism. Results of traditional and geometric morphometrics analyses revealed no sexual dimorphism in shape. All differences observed between the sexes are size related, with females bigger than males. Shape, however, is an important factor in the differentiation of at least two populations of this species.

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