Zardoya R, Meyer A
Museo Nacional de Ciencias Naturales, José Gutierrez Abascal, 2, 28006 Madrid, Spain.
Proc Natl Acad Sci U S A. 1998 Nov 24;95(24):14226-31. doi: 10.1073/pnas.95.24.14226.
Despite more than a century of debate, the evolutionary position of turtles (Testudines) relative to other amniotes (reptiles, birds, and mammals) remains uncertain. One of the major impediments to resolving this important evolutionary problem is the highly distinctive and enigmatic morphology of turtles that led to their traditional placement apart from diapsid reptiles as sole descendants of presumably primitive anapsid reptiles. To address this question, the complete (16,787-bp) mitochondrial genome sequence of the African side-necked turtle (Pelomedusa subrufa) was determined. This molecule contains several unusual features: a (TA)n microsatellite in the control region, the absence of an origin of replication for the light strand in the WANCY region of five tRNA genes, an unusually long noncoding region separating the ND5 and ND6 genes, an overlap between ATPase 6 and COIII genes, and the existence of extra nucleotides in ND3 and ND4L putative ORFs. Phylogenetic analyses of the complete mitochondrial genome sequences supported the placement of turtles as the sister group of an alligator and chicken (Archosauria) clade. This result clearly rejects the Haematothermia hypothesis (a sister-group relationship between mammals and birds), as well as rejecting the placement of turtles as the most basal living amniotes. Moreover, evidence from both complete mitochondrial rRNA genes supports a sister-group relationship of turtles to Archosauria to the exclusion of Lepidosauria (tuatara, snakes, and lizards). These results challenge the classic view of turtles as the only survivors of primary anapsid reptiles and imply that turtles might have secondarily lost their skull fenestration.
尽管经过了一个多世纪的争论，但龟鳖目（Testudines）相对于其他羊膜动物（爬行动物、鸟类和哺乳动物）的进化地位仍然不确定。解决这一重要进化问题的主要障碍之一是龟鳖目高度独特且神秘的形态，这导致它们传统上被置于双孔亚纲爬行动物之外，被认为是原始无孔亚纲爬行动物的唯一后代。为了解决这个问题，测定了非洲侧颈龟（Pelomedusa subrufa）的完整线粒体基因组序列（16787碱基对）。该分子包含几个不寻常的特征：控制区的一个（TA）n微卫星、五个tRNA基因的WANCY区域中缺少轻链复制起点、分隔ND5和ND6基因的一个异常长的非编码区、ATPase 6和COIII基因之间的重叠，以及ND3和ND4L推定开放阅读框中存在额外的核苷酸。对完整线粒体基因组序列的系统发育分析支持将龟鳖目置于短吻鳄和鸡（主龙类）进化枝的姐妹群位置。这一结果明确否定了热血假说（哺乳动物和鸟类之间的姐妹群关系），也否定了龟鳖目作为最基部现存羊膜动物的分类位置。此外，来自完整线粒体rRNA基因的证据支持龟鳖目与主龙类形成姐妹群关系，而排除鳞龙类（喙头蜥、蛇和蜥蜴）。这些结果挑战了龟鳖目是原始无孔亚纲爬行动物唯一幸存者的经典观点，并暗示龟鳖目可能是次生失去了头骨开孔。
