We describe here a new small bunodont metatherian from Priabonian deposits of the Geste Formation exposed in the Puna of Catamarca Province (Argentina). The material, an isolated right M2?, was recovered by screen-washing techniques and allows us to erect the new species Apeirodon sorianoi. The combination of diagnostic characters includes triangular occlusal pattern, bunoid, with an equally developed stylocone and cusp D, absence of cusp C, protoconal base wide, preparacrista and postmetacrista short, well-developed paracingulum, presence of double rank postvallum-prevallid shear, and presence of small paraconule and larger metaconule that is distolingually located. The overall morphology of Apeirodon more closely resembles Glasbius (particularly G.twitchelli) than any other Cretaceous-Paleogene American metatherian, supporting the largely accepted hypothesis proposing a common origin for some North and South American metatherian lineages. Apeirodon also resembles Reigia punae (another small metatherian recovered from the same stratigraphic levels), Chulpasia, Palangania, and specimens referred to Bobbschaefferia. Tentatively, we propose the inclusion of Apeirodon and Reigia as early divergent members of Polydolopimorphia based on the presence of bunodonty, enlarged stylocone and cusp D, and a distolingually-shifted metaconule. These features, incipiently developed in these late Eocene taxa, are emphasized in later representatives of the order. The presence of a generalized putative polydolopimorphian in Priabonian deposits of northwestern Argentina highlights the key temporal and spatial position of the region in the context of the evolution of Paleogene South American mammals.

中文翻译：

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来自阿根廷普纳晚始新世的新小型 Bunodont Metatherian

我们在此描述了一种新的小型 bunodont metatherian，它来自于卡塔马卡省（阿根廷）普纳的 Geste 组的 Priabonian 沉积物。该材料是一种孤立的右 M2?，通过筛网清洗技术回收，使我们能够建立新物种 Apeirodon sorianoi。诊断特征的组合包括三角形咬合模式，bunoid，具有同样发达的茎突和 D 尖峰，没有 C 尖峰，原锥基底部宽，前嵴前和后后嵴短，鞘管发育良好，存在双列后壁 - 前牙周剪切，和存在小锥旁突和位于舌侧的较大后锥突。Apeirodon 的整体形态比任何其他白垩纪 - 古近纪美国 metatherian 更类似于 Glasbius（特别是 G.twitchelli），支持被广泛接受的假设，即一些北美和南美超兽系的共同起源。Apeirodon 也类似于 Reigia punae（另一种从相同地层发现的小型后兽类）、Chulpasia、Palangania 和被称为 Bobbschaefferia 的标本。暂时性地，我们建议将 Apeirodon 和 Reigia 作为 Polydolopimorphia 的早期分歧成员，因为存在兔牙、增大的茎秆和尖头 D 以及向舌侧移动的后锥体。在这些晚始新世分类群中最初开发的这些特征在该目的后来代表中得到了强调。