Rasmussen A S, Janke A, Arnason U
Department of Genetics, University of Lund, Sweden.
J Mol Evol. 1998 Apr;46(4):382-8. doi: 10.1007/pl00006317.
The vertebrates are traditionally classified into two distinct groups, Agnatha (jawless vertebrates) and Gnathostomata (jawed vertebrates). Extant agnathans are represented by hagfishes (Myxiniformes) and lampreys (Petromyzontiformes), frequently grouped together within the Cyclostomata. Whereas the recognition of the Gnathostomata as a clade is commonly acknowledged, a consensus has not been reached regarding whether or not Cyclostomata represents a clade. In the present study we have used newly established sequences of the protein-coding genes of the mitochondrial DNA molecule of the hagfish to explore agnathan and gnathostome relationships. The phylogenetic analysis of Pisces, using echinoderms as outgroup, placed the hagfish as a sister group of Vertebrata sensu stricto, i.e., the lamprey and the gnathostomes. The phylogenetic analysis of the Gnathostomata identified a basal divergence between gnathostome fishes and a branch leading to birds and mammals, i.e., between "Anamnia" and Amniota. The lungfish has a basal position among gnathostome fishes with the teleosts as the most recently evolving lineage. The findings portray a hitherto unrecognized polarity in the evolution of bony fishes. The presently established relationships are incompatible with previous molecular studies.
传统上，脊椎动物被分为两个不同的类群：无颌类（无颌脊椎动物）和有颌类（有颌脊椎动物）。现存的无颌类以盲鳗（盲鳗目）和七鳃鳗（七鳃鳗目）为代表，它们常被归为圆口纲。虽然有颌类作为一个进化枝已得到普遍认可，但关于圆口纲是否代表一个进化枝尚未达成共识。在本研究中，我们利用新建立的盲鳗线粒体DNA分子蛋白质编码基因序列来探究无颌类和有颌类的关系。以棘皮动物为外类群对鱼类进行系统发育分析，结果将盲鳗置于狭义脊椎动物的姐妹群位置，即与七鳃鳗和有颌类处于同一位置。对有颌类的系统发育分析确定了有颌类鱼类与一个通向鸟类和哺乳动物的分支之间的基部分歧，即“无羊膜动物”和羊膜动物之间的分歧。肺鱼在有颌类鱼类中处于基部位置，硬骨鱼是最近进化的类群。这些发现揭示了硬骨鱼进化过程中迄今未被认识到的极性。目前建立的关系与之前的分子研究结果不一致。
