van Tuinen M, Sibley C G, Hedges S B
Department of Biology, Pennsylvania State University, University Park 16802, USA.
Mol Biol Evol. 2000 Mar;17(3):451-7. doi: 10.1093/oxfordjournals.molbev.a026324.
The traditional view of avian evolution places ratites and tinamous at the base of the phylogenetic tree of modern birds (Neornithes). In contrast, most recent molecular studies suggest that neognathous perching birds (Passeriformes) compose the oldest lineage of modern birds. Here, we report significant molecular support for the traditional view of neognath monophyly based on sequence analyses of nuclear and mitochondrial DNA (4.4 kb) from every modern avian order. Phylogenetic analyses further show that the ducks and gallinaceous birds are each other's closest relatives and together form the basal lineage of neognathous birds. To investigate why other molecular studies sampling fewer orders have reached different conclusions regarding neognath monophyly, we performed jackknife analyses on our mitochondrial data. Those analyses indicated taxon-sampling effects when basal galloanserine birds were included in combination with sparse taxon sampling. Our phylogenetic results suggest that the earliest neornithines were heavy-bodied, ground-dwelling, nonmarine birds. This inference, coupled with a fossil bias toward marine environments, provides a possible explanation for the large gap in the early fossil record of birds.
传统的鸟类进化观点认为平胸鸟和䳍形目鸟类处于现代鸟类（新鸟亚纲）系统发育树的基部。相比之下，最近的大多数分子研究表明，新颚类鸣禽（雀形目）构成了现代鸟类最古老的谱系。在此，我们基于对每个现代鸟类目核DNA和线粒体DNA（4.4 kb）的序列分析，报告了对新颚类单系性传统观点的重要分子支持。系统发育分析进一步表明，鸭类和鹑鸡类鸟类是彼此最亲近的亲属，并共同构成新颚类鸟类的基部谱系。为了探究为何其他采样鸟类目较少的分子研究在新颚类单系性方面得出了不同结论，我们对线粒体数据进行了刀切法分析。这些分析表明，当基部的鸡雁小纲鸟类与稀疏的分类群采样相结合时，存在分类群采样效应。我们的系统发育结果表明，最早的新鸟亚纲鸟类是体型较重、栖息于地面的非海洋鸟类。这一推断，再加上化石记录偏向海洋环境，为鸟类早期化石记录中的巨大空白提供了一种可能的解释。
