Zardoya R, Meyer A
Department of Ecology and Evolution, State University of New York, Stony Brook 11794-5245, USA.
Naturwissenschaften. 1997 Sep;84(9):389-97. doi: 10.1007/s001140050415.
The phylogenetic position of tetrapods relative to the other two living sarcopterygian lineages (lungfishes and the coelacanth) has been subject to debate for many decades, yet remains unresolved. There are three possible alternatives for the phylogenetic relationships among these three living lineages of sarcopterygians, i.e., lungfish as living sister group of tetrapods, the coelacanth as closest living relative of tetrapods, and lungfish and coelacanth equally closely related to tetrapods. To resolve this important evolutionary question several molecular data sets have been collected in recent years, the largest being the almost complete 28S rRNA gene sequences (about 3500 bp) and the complete mitochondrial genomes of the coelacanth and a lungfish (about 16,500 bp each). Phylogenetic analyses of several molecular data sets had not provided unequivocal support for any of the three hypotheses. However, a lungfish + tetrapod or a lungfish + coelacanth clade were predominantly favored over a coelacanth + tetrapod grouping when the entire mitochondrial genomes alone or in combination with the nuclear 28S rRNA gene data were analyzed with maximum parsimony, neighbor-joining, and maximum likelihood phylogenetic methods. Also, current paleontological and morphological data seem to concur with these molecular results. Therefore the currently available molecular data seems to rule out a coelacanth + tetrapod relationship, the traditional textbook hypothesis. These tentative molecular phylogenetic results point to the inherent difficulty in resolving relationships among lineages which apparently originated in rapid succession during the Devonian.
几十年来，四足动物相对于其他两个现存肉鳍鱼类谱系（肺鱼和腔棘鱼）的系统发育位置一直存在争议，至今仍未解决。对于这三个现存肉鳍鱼类谱系之间的系统发育关系，有三种可能的情况，即肺鱼是四足动物的现存姐妹群、腔棘鱼是四足动物最近的现存亲属，以及肺鱼和腔棘鱼与四足动物的亲缘关系同样密切。为了解决这个重要的进化问题，近年来已经收集了几个分子数据集，其中最大的是几乎完整的28S rRNA基因序列（约3500 bp）以及腔棘鱼和一种肺鱼的完整线粒体基因组（每种约16,500 bp）。对几个分子数据集的系统发育分析并未为这三种假说中的任何一种提供明确的支持。然而，当单独使用整个线粒体基因组或与核28S rRNA基因数据结合，采用最大简约法、邻接法和最大似然法进行系统发育分析时，肺鱼 + 四足动物或肺鱼 + 腔棘鱼分支比腔棘鱼 + 四足动物组合更受青睐。此外，目前的古生物学和形态学数据似乎与这些分子结果一致。因此，目前可用的分子数据似乎排除了腔棘鱼 + 四足动物的关系，即传统教科书上的假说。这些初步的分子系统发育结果表明，解决在泥盆纪期间显然快速相继起源的谱系之间的关系存在内在困难。
