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 mainly by masticatory feeding. Because the mouthpart muscles and organs primarily used in these feeding modes are different, 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 that the masticatory muscles are used less during suction feeding, whereas the tongue is used to perform force-intensive tasks. It has been suggested that the development of the palatine bone and the underdevelopment of the zygomatic arch in the Steller sea lion’s cranium represent characteristics of suction feeding.
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Acknowledgements
In this study, we partly used the specimens collected under the Comprehensive Project to Mitigate Fisheries Damages by Harmful Animals conducted by the Fishing Industry/Communities Promotion Organization. We thank all those who engaged in collecting and preparing Steller sea lion specimens, M. Eda at Hokkaido University Museum for kindly providing the opportunity to measure brown bear specimens, Y Watanuki and M Harunari for their constructive comments.
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This work was supported by ongoing institutional (Hokkaido University) funding. No additional grants to carry out or direct this particular research were obtained.
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Ryunosuke Yuge: Conceptualization, Formal Analysis, Methodology, Visualization, Writing – original draft. Yumi Kobayashi: Investigation, Writing – review & editing. Takeomi Isono: Investigation, Writing – review & editing. Orio Yamamura: Supervision, Writing – review & editing.
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Appendices
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Appendix 3
Changes in measurements relative to cranial length with age in Steller sea lions. a: length of palate, b: length of upper postcanine row c: breadth of auditory bulla, d: length of auditory bulla, e: length of orbit, f: breadth of orbit, g: height of cranium. 〇: female (age-estimated individuals), ●: male (age-estimated individuals), ◇: female (branding-marked individuals), ◆: male (branding-marked) individuals). Solid and dotted lines indicate linear regression curves for males and females, respectively
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Yuge, R., Kobayashi, Y., Isono, T. et al. Cranial ontogeny in Steller sea lions and relationships between cranial morphology and suction feeding. Mamm Res (2025). https://doi.org/10.1007/s13364-025-00819-9
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DOI: https://doi.org/10.1007/s13364-025-00819-9