Timing of ontogenetic changes of two cranial regions in Sotalia guianensis (Delphinidae)

Abstract

a b s t r a c tDespite the fact that heterochronic processes seem to be an important process determining morphological evolution of the delphinid skull, previous workers have not found allometric scaling as relevant factor in the differentiation within the genus Sotalia. Here we analyzed the skull ontogeny of the estuarine dolphin S. guianensis and investigate differential growth and shape changes of two cranial regionsthe neurocranium and the face -in order to evaluate the relevance of cranial compartmentalization on the ontogeny of this structure. Our results show that, even though both cranial regions stop growing at adulthood, the face has higher initial growth rates than the neurocranium. The rate of shape changes is also different for both regions, with the face showing a initially higher, but rapidly decreasing rate of change, while the neurocranium shows a slow decreasing rate, leading to persistent and localized shape changes throughout adult life, a pattern that could be related to epigenetic regional factors. The pattern of ontogenetic shape change described here is similar to those described for other groups of Delphinidae and also match intra and interspecific variation found within the family, suggesting that mosaic heterochrony could be an important factor in the morphological evolution of this group.

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

“…Mature franciscana dolphins showed a rostrum more aligned with the skull ‐and with the column‐ than immature dolphins. This fact has been also observed by Sydney et al () on Sotalia guianensis , who suggested that this feature is associated with a shift toward a more pelagic feeding.…”

“…The general direction of the shape change during postnatal ontogeny observed on P. blainvillei skull was expected according to the common pattern observed for mammals and particularly for odontocetes, that is, an enlargement of the rostral part of the skull, and a compression of the neurocranium, which is proportionally larger in earlier stages of postnatal development (Moore, ; Galatius et al, ; Sydney et al, ; Flores et al, ; Segura et al, ). Specific features, such as the early development of the premaxillaries and external nares, are probably restricted to odontocetes, because the skull function in this group is not only pointed to trophic and sensitive functions, but also to sound production mechanisms.…”

Skull ontogeny and modularity in two species ofLagenorhynchus: Morphological and ecological implications

“…A 3D digitizer Microscribe MX6DOF System (GoMeasured3D, Amherst, VA) was used to record 55 landmarks on each skull (Fig. , Supporting Information, Table S2), which were chosen following Sydney et al () with some modifications (del Castillo et al, , in press). We chose landmarks that represented the complete skull and allowed us to see important features of the development in each cranial module (see below).…”

“…Modules are composed by characters related ontogenetically or functionally which have high mutual influence, compared with those without functional commitments or unshared ontogenetic patterns. Modularity studies are uncommon in cetaceans, and have been mainly applied in evolutionary and ecological approaches (Sydney et al, ; Guidarelli et al, ). In this report, we also tested the presence of modules and their ontogenetic variation between both species.…”

Identifying design and reduction effects on lithic projectile point shapes

“…The modular shape spaces for the blade and the stem complement the dimensions of the integrated shape space and explain covariation patterns in the blade independent from changes occurring in the stem, and vice-versa.. The corresponding analysis was run in R Development Core Team (R Development Core Team, 2011) using the routine implemented by Sydney et al (2012).…”