Department of Earth and Space Sciences, University of Washington, Johnson Hall Rm-070, Box 351310, 3920 Okanogan Lane NE, Seattle, WA, 98195-1310, USA; Department of Paleontology, Burke Museum of Natural History and Culture, University of Washington, 4303 Memorial Way NE, Seattle, WA, 98195, USA.
Department of Anthropology, Brooklyn College, City University of New York, 2900 Bedford Avenue, Brooklyn, NY, 11210, USA; The Graduate Center, City University of New York, 365 Fifth Avenue, New York, NY, 10016, USA; New York Consortium in Evolutionary Primatology, 200 Central Park West, New York, NY, 10024, USA.
J Hum Evol. 2024 Jul;192:103500. doi: 10.1016/j.jhevol.2024.103500. Epub 2024 May 17.
Plesiadapiforms (putative stem primates) appear in the fossil record shortly after the Cretaceous/Paleogene boundary and subsequently radiated throughout the Paleocene into a taxonomically and ecomorphologically diverse group. The oldest known plesiadapiforms come from early Puercan (the oldest North American Land Mammal 'age' [NALMA] of the Cenozoic) deposits in northeastern Montana, and all records of Puercan plesiadapiforms are taxonomically restricted to members of the Purgatoriidae and the enigmatic genus Pandemonium. Plesiadapiform diversity substantially increased in the following Torrejonian NALMA, but the sparse record of faunas between the Puercan and the well-known middle and late Torrejonian has hampered our understanding of this important interval in early primate evolution. Here we report new plesiadapiform dental fossils from early Torrejonian (To1) deposits from the Tullock Member of the Fort Union Formation in northeastern Montana that record several poorly known taxa including members of the Purgatoriidae, Paromomyidae and Pandemonium, and that document the largest and most diverse assemblage of To1 plesiadapiforms known. We describe a new species of the purgatoriid Ursolestes (Ursolestes blissorum, sp. nov.) that represents the largest plesiadapiform known from the early Paleocene and, among other taxa, provides additional evidence that the temporal range of purgatoriids extended into the Torrejonian. Large sample sizes of the oldest known paromomyid, Paromomys farrandi, allowed us to document intraspecific variability and one undescribed tooth locus. Our observations illuminate changes in dental morphology of some taxa that occurred in To1 and may inform the acquisition of certain diagnostic plesiadapiform dental characters. We evaluate plesiadapiform species richness, mean body mass and body-mass disparity through the Paleocene and reveal unrecognized levels of richness in To1 and a general trend of stable body mass and body-mass disparity. Our findings contribute to documented patterns of plesiadapiform provincialism in the early Paleocene and shed light on the early stages of their Torrejonian radiation.
似哺乳爬行动物（假定的灵长类祖先）出现在白垩纪/古近纪之交之后不久的化石记录中，并随后在古新世辐射到一个在分类学和生态形态上多样化的群体。最古老的已知似哺乳爬行动物来自蒙大拿州东北部的早Puercan（新生代最早的北美陆地哺乳动物时代）沉积物，而所有 Puercan 似哺乳爬行动物的记录都仅限于 Purgatoriidae 和神秘的 Pandemonium 属。似哺乳爬行动物的多样性在随后的 Torrejonian NALMA 中大幅增加，但 Puercan 与著名的中晚期 Torrejonian 之间的动物群记录稀疏，这阻碍了我们对早期灵长类进化这一重要时期的理解。在这里，我们报告了来自蒙大拿州东北部 Fort Union 组的 Tullock 成员的早 Torrejonian（To1）沉积物中的新似哺乳爬行动物牙齿化石，这些化石记录了几个鲜为人知的分类群，包括 Purgatoriidae、Paromomyidae 和 Pandemonium，并且记录了已知的最大和最多样化的 To1 似哺乳爬行动物组合。我们描述了一种新的 Purgatoriidae 物种 Ursolestes（Ursolestes blissorum，sp. nov.），它是已知来自早古新世的最大似哺乳爬行动物，除其他分类群外，还提供了额外的证据表明 Purgatoriidae 的时间范围延伸到了 Torrejonian。最早的已知 Paromomyidae Paromomys farrandi 的大样本量使我们能够记录种内变异性和一个未描述的牙齿位置。我们的观察结果阐明了 To1 中某些分类群的牙齿形态发生的变化，并可能为某些诊断性似哺乳爬行动物牙齿特征的获得提供信息。我们通过古新世评估了似哺乳爬行动物的物种丰富度、平均体重和体重差异，并揭示了 To1 中未被识别的丰富度水平以及稳定的体重和体重差异的总体趋势。我们的发现有助于解释早古新世似哺乳爬行动物的地域主义模式，并揭示了它们在 Torrejonian 辐射的早期阶段。
