Meeting Abstract
The facial skeletons of extant adult cetaceans (whales, dolphins, porpoises) are highly divergent from those of other mammals. Their divergence is due, in part, to the posterodorsal position of the external nares (blowhole) and to braincase “telescoping,” an extraordinarily high degree of overlap between skull bones (Miller 1923). The arrangements of these features differ markedly among the two major sub-clades: toothed whales (odontocetes) and baleen whales (mysticetes). Detailed descriptions exist of adult morphologies, but the prenatal ontogeny that produces these morphologies is only minimally described. Here we investigate ontogenetic changes in orientation of several cranial features and growth of the bony elements associated with telescoping. We measured these changes from CT scans of fetal series of a dolphin species (Stenella attenuata) and the fin whale (Balaenoptera physalus) from the NMNH collection. Our data suggest that changes to the ventral skull are at the core of nasal passage reorientation, suggesting that the evolutionary changes to the face actually involve changes in relative growth to posterior regions of the skull. We also found that the overlapping of bones associated with telescoping develops progressively during the fetal period.
