Skull ontogeny and modularity in two species of Lagenorhynchus: Morphological and ecological implications.

Comparisons of skull shape between closely related species can provide information on the role that phylogeny and function play in cranial evolution. We used 3D-anatomical landmarks in order to study the skull ontogeny of two closely related species, Lagenorhynchus obscurus and Lagenorhynchus australis, with a total sample of 52 skulls. We found shared trends between species, such as the relative compression of the neurocranium and the enlargement of the rostrum during ontogeny. However, these are common mammalian features, associated with prenatal brain development and sensory capsules. Moreover, we found a posterior displacement of the external nares and infraorbital foramina, and a strong development of the rostrum in an anteroposterior direction. Such trends are associated with the process of telescoping and have been observed in postnatal ontogeny of other odontocetes, suggesting a constraint in the pattern. Interspecific differences related to the deepness of facial region, robustness of the feeding apparatus and rostrum orientation may be related with the specific lifestyles of L. obscurus and L. australis. We also tested the presence of three different modules in the skull (basicranium, neurocranium, rostrum), all of which presented strong integration. Only the rostrum showed a different ontogenetic trajectory between species. Even though we detected directional asymmetry, changes in this feature along ontogeny were not detectable. Because asymmetry may be related to echolocation, our results suggest a functional importance of directional asymmetry from the beginning of postnatal life. J. Morphol. 278:203-214, 2017. © 2016 Wiley Periodicals,Inc.

Ontogenetic development and sexual dimorphism of franciscana dolphin skull: A 3D geometric morphometric approach.

The aim of this work was to study the postnatal ontogenetic development of Pontoporia blainvillei skull, identifying major changes on shape, and relating them to relevant factors in the life history of the species. We analyzed a complete ontogenetic series (73♂, 83♀) with three-dimensional geometric morphometric techniques. Immature dolphins showed a very well-developed braincase and a poorly developed rostrum, and the principal postnatal changes affected the rostrum and the temporal fossa, both structures implied functionally to the feeding apparatus, thus suggesting a specialized mode for catch fast prey in P. blainvillei. Osseous elements associated with sound production were already well developed on immature dolphins, suggesting the importance of this apparatus since the beginning of postnatal life. Sexual dimorphism was detected on both shape and size variables. Females were bigger than males, in accordance with previous studies. Shape differences between sexes were found on the posterior part of premaxillaries and external bony nares (P < 0.01), suggesting that this sexual dimorphism is related to differences on vocalization capabilities.