[MARMAM] New paper: Determining Pacific walrus sex using mandible measurements

Casey Clark ctclark at alaska.edu
Sun Jun 21 12:16:13 PDT 2020

Hello MARMAM Members,

On behalf of my colleagues and myself, I am pleased to share our new paper “Determining sex of adult Pacific walruses from mandible measurements”, now available on early view at the Journal of Mammalogy. The article can be accessed here: https://bit.ly/2BtEpfC <https://bit.ly/2BtEpfC>

Taylor, N., C.T. Clark, N. Misarti, and L. Horstmann. 2020. Determining sex of adult Pacific walruses from mandible measurements. Journal of Mammalogy: XX(X):1-10 doi:10.1093/jmammal/gyaa051


Pacific walruses (Odobenus rosmarus divergens) play a vital role in Arctic marine ecosystems and the subsistence lifestyle of Alaska Native communities. Museum collections contain numerous archaeological and historic walrus specimens that have proven useful in a variety of studies; however, for many cases, the sex of these specimens is unknown. Sexes of adult (> 5 years determined by tooth aging) Atlantic walruses (Odobenus rosmarus rosmarus) have been accurately determined in previous studies using mandible measurements. We tested the validity of this approach for Pacific walruses, and used full fusion of the mandibular symphysis to define adults. Using high precision digital calipers (± 0.01 mm), four measurements were taken either on the left or right side of 91 walrus mandibles: 80 modern mandibles (70 known-sex specimens; 10 unknown-sex specimens) and 11 archaeological mandibles of unknown sex. We used linear discriminant function analysis (LDFA) to determine what measurements best distinguished Pacific walrus males from females. Minimum mandible thickness had the most predictive power, whereas mandible length, height, and depth, were less predictive. Posterior probabilities indicated that LDFA classified the known-sex Pacific walruses with 100% accuracy, and unknown sex with ≥ 90% probability. The ability to define the sex of unknown individuals accurately could greatly increase the sample size of future projects dealing with skeletal remains, and will improve future research efforts.

I am happy to provide a PDF of the article upon request. Please email me (ctclark at uw.edu <mailto:ctclark at uw.edu>) or the lead author (nataylor2 at alaska.edu <mailto:nataylor2 at alaska.edu>) if you are interested, or if you have any questions about the paper.

Best regards,

Casey Clark
JISAO Postdoc
University of Washington
ctclark at uw.edu <mailto:ctclark at uw.edu>
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