Asher Robert J
Museum of Zoology, University of Cambridge, Cambridge, UK.
BMC Evol Biol. 2007 Jul 3;7:108. doi: 10.1186/1471-2148-7-108.
Recent publications concerning the interordinal phylogeny of placental mammals have converged on a common signal, consisting of four major radiations with some ambiguity regarding the placental root. The DNA data with which these relationships have been reconstructed are easily accessible from public databases; access to morphological characters is much more difficult. Here, I present a graphical web-database of morphological characters focusing on placental mammals, in tandem with a combined-data phylogenetic analysis of placental mammal phylogeny.
The results reinforce the growing consensus regarding the extant placental mammal clades of Afrotheria, Xenarthra, Euarchontoglires, and Laurasiatheria. Unweighted parsimony applied to all DNA sequences and insertion-deletion (indel) characters of extant taxa alone support a placental root at murid rodents; combined with morphology this shifts to Afrotheria. Bayesian analyses of morphology, indels, and DNA support both a basal position for Afrotheria and the position of Cretaceous eutherians outside of crown Placentalia. Depending on treatment of third codon positions, the affinity of several fossils (Leptictis,Paleoparadoxia, Plesiorycteropus and Zalambdalestes) vary, highlighting the potential effect of sequence data on fossils for which such data are missing.
The combined dataset supports the location of the placental mammal root at Afrotheria or Xenarthra, not at Erinaceus or rodents. Even a small morphological dataset can have a marked influence on the location of the root in a combined-data analysis. Additional morphological data are desirable to better reconstruct the position of several fossil taxa; and the graphic-rich, web-based morphology data matrix presented here will make it easier to incorporate more taxa into a larger data matrix.
近期有关胎盘哺乳动物目间系统发育的出版物得出了一个共同的信号，包括四次主要的辐射演化，胎盘动物的根部存在一些模糊性。用于重建这些关系的DNA数据可从公共数据库轻松获取；而获取形态学特征则困难得多。在此，我展示了一个专注于胎盘哺乳动物的形态学特征图形网络数据库，并对胎盘哺乳动物系统发育进行了综合数据系统发育分析。
这些结果强化了关于非洲兽总目、异关节总目、真灵长总目和劳亚兽总目的现存胎盘哺乳动物类群的越来越多的共识。仅将未加权简约法应用于现存分类单元的所有DNA序列和插入缺失（indel）特征时，支持胎盘动物的根部位于鼠科啮齿动物；与形态学数据相结合时，根部则转移到了非洲兽总目。对形态学、indel和DNA进行的贝叶斯分析既支持非洲兽总目的基部位置，也支持白垩纪真兽类在胎盘动物冠群之外的位置。根据对第三密码子位置的处理方式，几种化石（细齿兽、古异蹄兽、土豚猬和三尖齿兽）的亲缘关系会有所不同，这突出了序列数据对缺少此类数据的化石的潜在影响。
综合数据集支持胎盘哺乳动物的根部位于非洲兽总目或异关节总目，而非刺猬或啮齿动物。即使是一个小的形态学数据集在综合数据分析中也会对根部的位置产生显著影响。需要更多的形态学数据来更好地重建几个化石分类单元的位置；这里展示的基于网络的、图形丰富的形态学数据矩阵将使将更多分类单元纳入更大的数据矩阵变得更加容易。
