Taylor Nathan, Clark Casey T, Misarti Nicole, Horstmann Lara
College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK, USA.
Joint Institute for the Study of Atmosphere and Ocean, University of Washington, Seattle, WA, USA.
J Mammal. 2020 Jun 20;101(4):941-950. doi: 10.1093/jmammal/gyaa051. eCollection 2020 Aug 31.
Pacific walruses () 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 () 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.
太平洋海象（）在北极海洋生态系统以及阿拉斯加原住民社区的自给自足生活方式中发挥着至关重要的作用。博物馆藏品包含众多考古和历史海象标本，这些标本已被证明在各种研究中很有用；然而，在许多情况下，这些标本的性别是未知的。在先前的研究中，已通过下颌骨测量准确确定了成年（通过牙齿老化确定年龄大于5岁）大西洋海象（）的性别。我们测试了这种方法对太平洋海象的有效性，并使用下颌联合的完全融合来定义成年海象。使用高精度数字卡尺（精度为±0.01毫米），在91个海象下颌骨的左侧或右侧进行了四项测量：80个现代下颌骨（70个已知性别的标本；10个未知性别的标本）和11个未知性别的考古下颌骨。我们使用线性判别函数分析（LDFA）来确定哪些测量最能区分太平洋海象的雄性和雌性。下颌骨最小厚度具有最强的预测能力，而下颌骨长度、高度和深度的预测能力较弱。后验概率表明，LDFA对已知性别的太平洋海象的分类准确率为100%，对未知性别的分类概率≥90%。准确确定未知个体性别的能力可以大大增加未来处理骨骼遗骸项目的样本量，并将改善未来的研究工作。
