A new otter of giant size, Siamogale melilutra sp. nov. (Lutrinae: Mustelidae: Carnivora), from the latest Miocene Shuitangba site in north-eastern Yunnan, south-western China, and a total-evidence phylogeny of lutrines

Otters (subfamily Lutrinae) are semi-aquatic predators in the family Mustelidae. Modern otters have a worldwide distribution but their fossil record is poor, often consisting of fragmentary jaws and teeth. Multiple lineages have developed bunodont dentitions with enlargements of molars, usually for cracking molluscs or other hard foods. Some lineages have evolved badger-like teeth and, as a result, were often confused with melines (Old World badger clade). Siamogale thailandica Ginsburg, Invagat, & Tassy, 1983 from the middle Miocene basin of Mae Moh in northern Thailand is one such species, whose fragmentary dental remains have thus far impeded our understanding. A new species of fossil otter, Siamogale melilutra sp. nov., represented by a nearly complete cranium, mandible and partial skeletons of at least three individuals, was recovered from the latest Miocene (∼6.2 Ma) lignite beds of the Shuitangba Site in north-eastern Yunnan Province, south-western China. Computed tomography (CT) restoration of the crushed skull reveals a combination of otter-like and badger-like cranial and dental characteristics. The new species belongs to the Lutrinae because of its possession of a large infraorbital canal and ventral expansion of the mastoid process, among other traits. A distally expanded M1, however, gives a badger-like appearance. In overall morphology the Shuitangba otter is closest to Siamogale thailandica. A previously described jaw (‘Lutra’ aonychoides) from the early Pliocene of the Yushe Basin in north China is also here referred to S. melilutra. No previous attempt has been made to provide a global phylogenetic framework for otters. We present the first combined morphological and molecular (nuclear and mitochondrial DNAs) character matrices of five extant (Pteronura, Lontra, Enhydra, Aonyx, Lutra) and eight extinct genera (Tyrrhenolutra, Paralutra, Paludolutra, Enhydritherium, Siamogale, Vishnuonyx, Sivaonyx, Enhydriodon) to better understand the evolution of bunodont otters. Parsimony and Bayesian analyses consistently recover an eastern Asian clade that includes forms from Shuitangba, Yushe and Mae Moh, all of which are referred to Siamogale. http://zoobank.org/urn:lsid:zoobank.org:pub:5C637018-0772-4C78-AA4B-783B71085D9D

海獭（亚科 Lutrinae）是鼬科中的半水生捕食者。现代海獭具有全球分布，但它们的化石记录匮乏，通常仅由破碎的下颌骨和牙齿组成。多个谱系发展出了具有牙齿扩大现象的多尖齿列，通常用于裂开贝类或其他硬质食物。某些谱系进化出了獾类牙齿，因此常与獾属（旧大陆獾类群）混淆。来自泰国北部玛叻府中部中新世盆地的 Siamogale thailandica Ginsburg, Invagat, & Tassy, 1983 即为其中之一，其破碎的牙齿遗骸至今阻碍了我们对其的理解。一种新的化石海獭物种，Siamogale melilutra sp. nov.，由近乎完整的颅骨、下颌骨以及至少三个个体的部分骨骼构成，被发掘自中国西南部云南省东北部的蜀堂坝遗址的最新中新世（约620万年前）的褐煤层中。计算机断层扫描（CT）对破碎颅骨的重建揭示了海獭与獾类颅骨和牙齿特征的结合。新物种属于 Lutrinae 亚科，因其具有大型眶下管和乳突过程的腹侧扩张等特征。然而，远端扩大的第一磨牙却呈现出獾类的特征。在整体形态上，蜀堂坝海獭与 Siamogale thailandica 最为接近。此外，一种先前描述的下颌骨（“Lutra” aonychoides）来自中国北部玉树盆地的早更新世，也被归入 S. melilutra。迄今为止，尚未有任何尝试为海獭提供全球系统发育框架。我们展示了五种现存（Pteronura, Lontra, Enhydra, Aonyx, Lutra）和八种灭绝（Tyrrhenolutra, Paralutra, Paludolutra, Enhydritherium, Siamogale, Vishnuonyx, Sivaonyx, Enhydriodon）属的形态学和分子（核和线粒体DNA）特征矩阵，以更好地理解多尖齿海獭的进化。简约法和贝叶斯分析一致地恢复了一个东亚谱系，包括蜀堂坝、玉树和玛叻府的形态，均归入 Siamogale。更多信息请访问：http://zoobank.org/urn:lsid:zoobank.org:pub:5C637018-0772-4C78-AA4B-783B71085D9D