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Total Dental Occlusal Area as a Feeding Constraint Feature in Extant Walruses (Odobenus rosmarus), and Implications for the Evolution of Molluscivory in Odobenidae

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Abstract

Mammalian dental formulae often are highly conserved, at least at a generic level. In walruses (Odobenus rosmarus), the constraints of dentition in light of documented high variability in tooth counts among walrus are examined. We propose that walruses do not have a constrained dental formula in terms of tooth position or tooth count. Instead, while walrus tooth counts vary, total occlusal area (TOA) is constrained relative to body mass, independent of tooth position or count. Nearly three-fourths of the 70 individuals sampled here had dentitions deviating from the previously reported dental formula of 1/1, 1/0, 3/3, 0/0, but there is a strong relationship between body size and total occlusal area. While the positive correlation between body size and TOA is consistent between sexes, the slope of the relationship differs significantly, suggesting an important sexual dimorphism in more than just walrus body size or tusk morphology. It is unclear if walrus teeth are involved at all in feeding, so TOA may impact positioning of prey during feeding or be completely independent of prey acquisition or feeding. Limited field observations support the hypothesis that dentition may play some role in prey positioning, with males feeding on both larger species and larger individuals of bivalves than females. Differences in food availability to individuals of differing body size have implications for conservation of walruses in the face of climate change and interactions with human fisheries, as well as diagnosing fossil taxa frequently defined in part by dental count. Extant walruses also may present an example of linking increased trait variability with the relaxation of functional constraints in response to shifting ecological roles.

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Availability of Data and Materials

All raw measurements generated or analyzed for this study are included in this published article and Online Resource 1. Original photographs of specimens are not publicly available, as it violates use agreements from museum repositories, but are available from the corresponding author on reasonable request, with the exception of the UAF specimens, which are available associated with their specimen numbers via Arctos.

Code Availability

All R code is available in Online Resource 2.

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Acknowledgements

Thank you to A. Nelson, for asking the questions that inspired this project. Thank you to E. White (University of Oregon) for access and photographing the University of Oregon specimen as well as her superb artwork on the walrus skull diagram, to C. Conroy for access to the UC Berkeley MVZ specimen, to P. Holroyd for access to the UCMP specimens as well as invaluable discussion and suggestions for this project, to M. Dickson for access to the AMNH material included, to A. Gunderson for many photographs of the UAM collections walruses, to K. Stilson and F. Socki for photographs of the FMNH specimens and to B. Patterson, L. Heaney, R. Banasiak, L. Smith, and B. Marks for access to those specimens. We also thank D. Reuter for taking the UWBM photographs and J. Bradley for access to the specimens. Thank you to K. Prassack for some initial review of this manuscript, and R. Boessenecker and A. Poust for their extremely helpful reviews on this manuscript. Finally, R.I.P to E.T. the walrus who not only provided inspiration for this article, but was a deciding factor in the lead author becoming a scientist.

Funding

Funding to travel to the AMNH was provided by the Theodore Roosevelt Memorial Fund of the American Museum of Natural History. Funding to travel to the UCMP was in part provided by a UCMP Samuel P. Welles Fund grant. This research was supported in part by an NSF grant (DEB-1256897) to SSBH and S. Price.

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Authors and Affiliations

  1. Department of Geology, Pomona College, Claremont, CA, USA

    Win N. F. McLaughlin

  2. Department of Earth Sciences, University of Oregon, Eugene, OR, USA

    Edward B. Davis & Samantha S. B. Hopkins

  3. Department of Biological Sciences, University of Oregon, Eugene, OR, USA

    Caitlyn J. Boatman

  4. Clark Honors College, University of Oregon, Eugene, OR, USA

    Caitlyn J. Boatman & Samantha S. B. Hopkins

  5. University of Oregon Museum of Natural and Cultural History, Eugene, OR, USA

    Edward B. Davis & Samantha S. B. Hopkins

Authors
  1. Win N. F. McLaughlin
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  2. Caitlyn J. Boatman
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  3. Edward B. Davis
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  4. Samantha S. B. Hopkins
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Contributions

All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Win McLaughlin. Data collection was also performed by Caitlyn Boatman. Data analysis was also performed by Edward Davis. The first draft of the manuscript was written by Win McLaughlin and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Win N. F. McLaughlin.

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Appendix

Appendix

Specimens Included in Study

USNM-6780, AMNH-19267, AMNH-19271, AMNH-20046, AMNH-77938, AMNH-77940, AMNH-90779, AMNH-90783, AMNH-90877, AMNH-207765, AMNH-41216, AMNH-1562, MNCH-D632, MVZ-184134, MVZ-106189, MVZ-106189, MVZ-119066, MVZ-184134, MVZ-96097, MVZ-125567, MVZ-96099, MVZ-125559, MVZ-57327, UAM-14793, UAM-16586, UAM-12075, UAM-99578, UAM-87009, UAM-87003, UAM-87001, UAM-16593, UAM-16592, UAM-16591, UAM-16588, UAM-12086, UAM-12085, UAM-12084, UAM-12083, UAM-12082, UAM-12081, UAM-12079, UAM-12078, UAM-12077, UAM-12076, UAM-12075, UAM-7277, UAM-11700, UAM-11696, UAM-11694, UAM-10538, FMNH-26888, FMNH-29171, FMNH-5508, FMNH-26809, FMNH-766, FMNH-140831, FMNH-26889, UWBM-34502, UWBM-36990, UWBM-82591, UWBM-82590, UWBM-51203, UWBM-82506, UWBM-82507, UWBM-12027, UWBM-12028 UWBM-51201, UWBM-41984, UWBM-35215, UWBM-80659, NMNH-550410, NMNH-16437, NMNH-402/403, NMC-38490, USNM-276030, USNM-550413, USNM-22014, USNM-267962, USNM-267965, USNM-276624, USNM-291842.

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McLaughlin, W.N.F., Boatman, C.J., Davis, E.B. et al. Total Dental Occlusal Area as a Feeding Constraint Feature in Extant Walruses (Odobenus rosmarus), and Implications for the Evolution of Molluscivory in Odobenidae. J Mammal Evol 29, 571–583 (2022). https://doi.org/10.1007/s10914-022-09603-x

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