有关来自中国侏罗纪（距今约1.60亿-1.65亿年前）的两个新发现的化石的独立报告，产生了对哺乳动物起源的相互冲突的重建结果。Haramiyids是中生代哺乳动物，具有奇特的、高度衍生的、与啮齿类动物相似的牙齿。由于这一点，它们过去一直被认为与“多瘤齿兽类”是同类，后者是一类体型较大的、高度成功的、与啮齿类相似的哺乳动物，直到始新世才灭绝。Haramiyids所存在的问题是，它们直到不久前还仅仅通过牙齿而为人们所知。由Jin Meng及其同事发表的一篇报告显示了一个要完整得多的生物（形象），其特征说明它们与“多瘤齿兽类”是同类，从而证实了早先的观点，但也说明现存哺乳动物的起源可能远在“三叠纪”。相比之下，由Zhe-Xi Luo及其同事描述的Haramiyids在下巴和脚踝的很多特征上的原始程度令人吃惊，说明Haramiyids在哺乳动物这个分支上是很原始的，与“多瘤齿兽类”根本没有关系。二者观点的这种截然对立说明了我们对化石的了解是多么得少，而对化石的解读是了解哺乳动物早期演化的关键。（生物谷 Bioon.com）
生物谷推荐的英文摘要
Nature doi:10.1038/nature12429
A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations
Chang-Fu Zhou, Shaoyuan Wu, Thomas Martin & Zhe-Xi Luo
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.
Nature doi:10.1038/nature12353
A new arboreal haramiyid shows the diversity of crown mammals in the Jurassic period
Xiaoting Zheng, Shundong Bi, Xiaoli Wang & Jin Meng
A major unsolved problem in mammalian evolution is the origin of Allotheria, including Multituberculata and Haramiyida1, 2, 3, 4, 5. Multituberculates are the most diverse and best known Mesozoic era mammals and ecologically resemble rodents, but haramiyids are known mainly from isolated teeth, hampering our search for their phylogenetic relationships. Here we report a new haramiyid from the Jurassic period of China, which is, to our knowledge the largest reported so far. It has a novel dentition, a mandible resembling advanced multituberculates and postcranial features adapted for arboreal life. Our phylogenetic analysis places Haramiyida within crown Mammalia, suggesting the origin of crown Mammalia in the Late Triassic period and diversification in the Jurassic, which contrasts other estimated divergence times of crown Mammalia6, 7, 8. The new haramiyid reveals additional mammalian features of the group, helps to identify other haramiyids represented by isolated teeth, and shows again that, regardless of various phylogenetic scenarios, a complex pattern of evolution involving many convergences and/or reversals existed in Mesozoic mammals.
