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Tribosphenic mammal from the North American Early Cretaceous

机译：北美早白垩世的Tribosphenic哺乳动物

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摘要

The main groups of living mammals, marsupials and eutherians, are presumed to have diverged in the Early Cretaceous, but their early history and biogeography are poorly understood. Dental remains have suggested that the eutherians may have originated in Asia, spreading to North America in the Late Cretaceous, where an endemic radiation of marsupials was already well underway. Here I describe a new tribosphenic mammal (a mammal with lower molar heels that are three-cusped and basined) from the Early Cretaceous of North America, based on an unusually complete specimen. The new taxon bears characteristics (molar-ized last premolar, reduction to three molars) otherwise known only for Eutheria among the tribosphenic mammals. Morpho-metric analysis and character comparisons show, however, that its molar structure is primitive (and thus phylogenetically uninfor-mative), emphasizing the need for caution in interpretation of isolated teeth. The new mammal is approximately contemporaneous with the oldest known Eutheria from Asia. If it is a eutherian, as is indicated by the available evidence, then this group was far more widely distributed in the Early Cretaceous than previously appreciated. An early presence of Eutheria in North America offers a potential source for the continent's Late Cretaceous radiations, which have, in part, proven difficult to relate to contemporary taxa in Asia.
机译：据推测，主要的活体哺乳动物，有袋动物和真人动物在白垩纪早已发生分歧，但对它们的早期历史和生物地理学知之甚少。牙齿遗骸表明，这些有风植物可能起源于亚洲，并在白垩纪晚期扩散到北美，那里有袋有毒动物的流行已经在进行中。在这里，我根据一个异常完整的标本，描述了一种来自北美白垩纪早期的新的摩擦性哺乳动物（一种具有三尖齿和下颌的低臼齿跟的哺乳动物）。新的分类单元具有特征（磨牙化的最后一个前磨牙，减少到三个磨牙），否则在摩擦性哺乳动物中仅对Eutheria已知。然而，形态计量学分析和特征比较表明，它的臼齿结构是原始的（因此在系统发育上是无信息的），强调在解释离体牙齿时需要谨慎。这种新的哺乳动物大约与来自亚洲的最古老的Eutheria同时期。如现有证据所表明的那样，如果它是欧氏体的话，那么该群在白垩纪早期的分布比以前所认识的要广泛得多。北美最早出现的Eutheria为该大陆的晚白垩世辐射提供了潜在的来源，而在一定程度上，事实证明，与亚洲的现代生物分类无关。

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  • 来源
    《Nature》 |1999年第6751期|p.363-366|共4页
  • 作者

    R L Cifelli;

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  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然科学总论;
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