Journal
JOURNAL OF MAMMALOGY
Volume 97, Issue 5, Pages 1345-1354Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/jmammal/gyw101
Keywords
asymmetry; Cephalorhynchus commersonii; cranial ontogeny; geometric morphometrics
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Funding
- Agencia Nacional de Promocion Cientifica y Tecnologica, Argentina [PICT 2012-1583, PICT 2014-3182]
- Consejo Nacional de Investigaciones Cientificas y Tecnicas, Argentina
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Commerson's dolphin, Cephalorhynchus commersonii, is one of the smallest species of odontocete cetaceans. We aimed to study the postnatal cranial ontogeny of C. commersonii through geometric morphometric technique, analyzing the postnatal ontogeny of the symmetric and asymmetric components of shape and providing information about sexual dimorphism affecting cranial shape and size. We digitized 57 landmarks in a sample of 139 crania of an ontogenetic series. Our results indicate that C. commersonii presents sexual size dimorphism of cranium in adults, but not shape dimorphism. Major changes between juveniles and adults were associated with lengthening of the rostrum and accentuation of telescoping, as observed in other odontocetes. We found that the degree of asymmetry has a very subtle but still significant change during ontogeny, which may have functional implications. We also observed little general variation in skull shape during postnatal development, supporting the idea of the conservatism of young-like characters in adults of C. commersonii. In accordance with this, we detect a very early attainment of stability of shape and size, being statistically similar in males and females. Differences in overall cranial shape and growth patterns in C. commersonii and Pontoporia blainvillei can be functionally associated to specific modes of feeding, suggesting also differences in the melon morphology.
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