Northernmost record of the Metatheria: a new Late Cretaceous pediomyid from the North Slope of Alaska

Northernmost record of the Metatheria: a new Late Cretaceous pediomyid from the North Slope of Alaska

The northernmost record of Metatheria, Unnuakomys hutchisoni gen. et sp. nov., is described from the Pediomys Point locality in Upper Cretaceous (lower Maastrichtian) strata of the Prince Creek Formation cropping out along the Colville River on the North Slope of Alaska, USA (70°N). Based on over 60 specimens (including tooth-bearing dentaries and a maxillary fragment), the new taxon is unusual in having two well-developed stylar cusps in the C position flanking the deepest part of the ectoflexus. To examine the relationship between U. hutchisoni and other metatherians, U. hutchisoni was scored into the taxon character matrix of other studies. Our results corroborate prior studies that suggest the new Alaskan pediomyid. However, in contrast to other studies, we do not recover a sister-group relationship between U. hutchisoni and Pediomys elegans. Rather, our study suggests that U. hutchisoni is more closely allied with Aquilan species Iqualadelphis lactea and ?Aquiladelphis laurae. Teeth of U. hutchisoni greatly outnumber those recovered from other mammals at Pediomys Point, like Late Cretaceous localities in the Western Interior where metatherians are among the most abundant mammalian fossils. However, what differs between Late Cretaceous mid-latitude localities and the assemblage from the North Slope of Alaska is metatherian richness. Whereas other studies have reported up to a dozen species of metatherians from Late Cretaceous mid-latitude North American assemblages, to date all the metatherian teeth collected from Pediomys Point appear to belong to just U. hutchisoni. A sampling bias may play a role in this pattern. This can be tested through additional collection from the Prince Creek Formation. However, the abundance of U. hutchisoni at Pediomys Point implies that this tiny metatherian thrived in an environment well above the Arctic Circle whose climatic extremes may have acted as a biogeographical filter to other metatherians. As the first mammal to be described from the Prince Creek Formation, U. hutchisoni provides support for the existence of a northern high-latitude early Maastrichtian faunal province identified by others on the basis of its distinctive dinosaurian fauna – the Paaŋaqtat Province. http://zoobank.org/urn:lsid:zoobank.org:pub:0EF38E01-2FF4-4698-A3AD-97CF2EE6847A

在美国阿拉斯加北坡科尔维尔河沿岸出露的普林斯溪组上白垩统（马斯垂克阶下部）地层的佩迪奥米斯角地区（北纬70°），描述了后兽亚纲最北的记录——新属新种汉氏昂努阿克鼠（Unnuakomys hutchisoni gen. et sp. nov.）。基于60多件标本（包括带有牙齿的下颌骨和一块上颌骨碎片），这个新分类群不同寻常之处在于，在位于外弯最深部分两侧的C位置有两个发育良好的齿柱尖。为了研究汉氏昂努阿克鼠与其他后兽亚纲动物的关系，将汉氏昂努阿克鼠纳入了其他研究的分类群特征矩阵中。我们的结果证实了先前的研究，表明它是一种新的阿拉斯加佩迪奥米鼠科动物。然而，与其他研究不同的是，我们没有发现汉氏昂努阿克鼠与优雅佩迪奥米鼠（Pediomys elegans）之间存在姐妹群关系。相反，我们的研究表明，汉氏昂努阿克鼠与阿奎兰物种乳白伊夸尔德菲斯兽（Iqualadelphis lactea）和？劳拉阿奎尔德菲斯兽（Aquiladelphis laurae）的亲缘关系更为密切。在佩迪奥米斯角，汉氏昂努阿克鼠的牙齿数量远远超过从其他哺乳动物中发现的数量，就像北美西部内陆的晚白垩世地点一样，在后兽亚纲动物是最丰富的哺乳动物化石之一。然而，晚白垩世中纬度地点和阿拉斯加北坡的动物群之间的差异在于后兽亚纲动物的丰富度。其他研究报告称，在北美晚白垩世中纬度动物群中多达十几种后兽亚纲动物，而到目前为止，从佩迪奥米斯角收集到的所有后兽亚纲动物牙齿似乎都只属于汉氏昂努阿克鼠。抽样偏差可能在这种模式中起作用。这可以通过对普林斯溪组进行更多的采集来检验。然而，汉氏昂努阿克鼠在佩迪奥米斯角的大量存在意味着这种小型后兽亚纲动物在北极圈以北的环境中茁壮成长，那里的极端气候可能对其他后兽亚纲动物起到了生物地理过滤器的作用。作为从普林斯溪组描述的第一种哺乳动物，汉氏昂努阿克鼠为其他人根据其独特的恐龙动物群——帕纳克塔特省所确定的北高纬度早马斯垂克阶动物地理区的存在提供了支持。http://zoobank.org/urn:lsid:zoobank.org:pub:0EF38E01 - 2FF4 - 4698 - A3AD - 97CF2EE6847A