Cranial ontogeny in Steller sea lions: Relationships between cranial morphology and suction feeding

Abstract

Suction feeding is a specific behavior in pinnipeds such as the Steller sea lion (Eumetopias jubatus), whereas the phylogenetically related brown bear (Ursus arctos) ingests by masticatory feeding. Because these feeding modes use different organs, the morphology and ontogeny of the cranial bones of these species may be related to differences in their feeding behavior. In this study, we performed multiple regression analyses to compare the ontogeny of Steller sea lion and brown bear cranial morphology by species and sex, using age, species, and the age × species interaction as explanatory variables and site measurements standardized by cranial length as response variables. The results showed that the palatine bone in both sexes widened with age in Steller sea lions compared to brown bears, whereas the width of the zygomatic arch was less developed in female Steller sea lions than in brown bears. This result may reflect the fact that the masticatory muscles are used less during suction feeding, whereas the tongue is used to perform force-intensive tasks. These results are consistent with previous studies on Carnivora and suggest that the development of the palatine bone and underdevelopment of the zygomatic arch represent characteristics of suction feeding.