A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations
A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations
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DOI：
10.1038/nature12429
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发表时间：
2013-08
期刊：
影响因子：
64.8
通讯作者：
Chang-Fu Zhou;Shaoyuan Wu;T. Martin;Zhe‐Xi Luo
中科院分区：
文献类型：
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作者：
Chang-Fu Zhou;Shaoyuan Wu;T. Martin;Zhe‐Xi Luo
哺乳动物最早的进化和哺乳动物特征的起源可以追溯到三叠纪和侏罗纪时期的哺乳动物，它们是现存哺乳动物的灭绝近亲。在这里，我们描述了一个来自中侏罗世的新化石，它具有下颌中耳，胸腰椎骨的渐变过渡和原始踝关节特征，但高度衍生的臼齿具有高冠和多根部分融合。上磨牙有纵向的尖牙列，与下磨牙的尖牙列交替咬合。这种咀嚼植物的特化表明，在冠类哺乳动物出现之前，食草动物已经在哺乳动物中进化了。这个新物种具有象齿目进化支系独特的牙齿特征，尽管它在侏罗纪时期分布广泛，但以前只有孤立的牙齿。这种棘齿兽是陆生动物，步态灵活，类似于现存的陆生哺乳动物，如犰狳或岩狸。它的皮毛证实了哺乳动物的被皮早在现存哺乳动物的共同祖先之前就已经出现了。
The earliest evolution of mammals and origins of mammalian features can be traced to the mammaliaforms of the Triassic and Jurassic periods that are extinct relatives to living mammals. Here we describe a new fossil from the Middle Jurassic that has a mandibular middle ear, a gradational transition of thoracolumbar vertebrae and primitive ankle features, but highly derived molars with a high crown and multiple roots that are partially fused. The upper molars have longitudinal cusp rows that occlude alternately with those of the lower molars. This specialization for masticating plants indicates that herbivory evolved among mammaliaforms, before the rise of crown mammals. The new species shares the distinctive dental features of the eleutherodontid clade, previously represented only by isolated teeth despite its extensive geographic distribution during the Jurassic. This eleutherodontid was terrestrial and had ambulatory gaits, analogous to extant terrestrial mammals such as armadillos or rock hyrax. Its fur corroborates that mammalian integument had originated well before the common ancestor of living mammals.