Centre for Macroevolution and Macroecology, School of Botany and Zoology, Australian National University, Canberra, ACT 0200, Australia.
Syst Biol. 2010 Jan;59(1):90-107. doi: 10.1093/sysbio/syp079. Epub 2009 Nov 13.
Ratites are large, flightless birds and include the ostrich, rheas, kiwi, emu, and cassowaries, along with extinct members, such as moa and elephant birds. Previous phylogenetic analyses of complete mitochondrial genome sequences have reinforced the traditional belief that ratites are monophyletic and tinamous are their sister group. However, in these studies ratite monophyly was enforced in the analyses that modeled rate heterogeneity among variable sites. Relaxing this topological constraint results in strong support for the tinamous (which fly) nesting within ratites. Furthermore, upon reducing base compositional bias and partitioning models of sequence evolution among protein codon positions and RNA structures, the tinamou-moa clade grouped with kiwi, emu, and cassowaries to the exclusion of the successively more divergent rheas and ostrich. These relationships are consistent with recent results from a large nuclear data set, whereas our strongly supported finding of a tinamou-moa grouping further resolves palaeognath phylogeny. We infer flight to have been lost among ratites multiple times in temporally close association with the Cretaceous-Tertiary extinction event. This circumvents requirements for transient microcontinents and island chains to explain discordance between ratite phylogeny and patterns of continental breakup. Ostriches may have dispersed to Africa from Eurasia, putting in question the status of ratites as an iconic Gondwanan relict taxon.
平胸类是大型的、不会飞的鸟类，包括鸵鸟、美洲鸵、几维鸟、鸸鹋和食火鸡，以及已灭绝的成员，如恐鸟和象鸟。先前基于完整线粒体基因组序列的系统发育分析，加强了平胸类是单系群、而䳍形目是其姊妹群的传统观念。然而，在这些研究中，平胸类单系性是通过在分析中对变异位点的速率异质性建模来强制实现的。放松这个拓扑约束，就会强烈支持䳍形目（会飞）在平胸类内部的分支。此外，在减少碱基组成偏差并在蛋白质密码子位置和 RNA 结构之间对序列进化的分区模型后，鹤鸵-恐鸟分支与几维鸟、鸸鹋和食火鸡聚在一起，而将逐渐变得更加分化的美洲鸵鸟和鸵鸟排除在外。这些关系与来自大型核数据集的最新结果一致，而我们强烈支持的鹤鸵-恐鸟分支的发现，进一步解决了古颚总目的系统发育问题。我们推断，在与白垩纪-第三纪灭绝事件时间上密切相关的情况下，平胸类多次失去了飞行能力。这规避了对暂时的微大陆和岛链的要求，从而解释了平胸类的系统发育与大陆分裂模式之间的不一致性。鸵鸟可能是从欧亚大陆扩散到非洲的，这使得平胸类作为冈瓦纳古陆残留的标志性分类群的地位受到质疑。
