Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA.
Mol Phylogenet Evol. 2010 May;55(2):572-9. doi: 10.1016/j.ympev.2010.01.037. Epub 2010 Feb 4.
Hammerhead sharks (Family Sphyrnidae) get their name from their laterally expanded, dorsal-ventrally compressed head, a structure referred to as the cephalofoil. Species within the family vary for head size and shape and for body size in ways that are functionally significant. Here we infer the phylogeny for all species within the family based on analysis of mitochondrial and nuclear genes amounting to 6292 base pairs. Mixed model Bayesian analysis of the concatenated data and Bayesian estimation of the species tree (BEST) converged on the same topology of the relationships. Shimodaira-Hasegawa tests revealed that all previously proposed hypotheses could be refuted by the data. The new hypothesis for the group suggests that the ancestor of all extant sharks was large (>200 cms) and that small body size probably evolved twice at different times and places. Moreover, the results suggest that once the cephalofoil evolved, it underwent divergent evolution in different lineages presumably in response to unique selective regimes.
双髻鲨（Sphyrnidae 科）的名字来源于其侧向扩展、背腹压缩的头部，这种结构被称为头翼。该科内的物种在头部大小和形状以及身体大小方面存在功能上显著的差异。在这里，我们基于线粒体和核基因的分析推断了该科内所有物种的系统发育，总共有 6292 个碱基对。对连接数据的混合模型贝叶斯分析和贝叶斯估计的种系发生树（BEST）收敛于相同的关系拓扑结构。Shimodaira-Hasegawa 检验表明，所有以前提出的假说都可以被数据所否定。该小组的新假说表明，所有现存鲨鱼的祖先体型都很大（>200 厘米），而小体型可能在不同的时间和地点两次进化而来。此外，结果表明，一旦头翼进化，它就在不同的谱系中经历了趋异进化，可能是为了应对独特的选择机制。
