Thuy Ben, Stöhr Sabine
Department of Palaeontology, Natural History Museum Luxembourg, Luxembourg-city, Luxembourg.
Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.
PLoS One. 2016 May 26;11(5):e0156140. doi: 10.1371/journal.pone.0156140. eCollection 2016.
Ophiuroid systematics is currently in a state of upheaval, with recent molecular estimates fundamentally clashing with traditional, morphology-based classifications. Here, we attempt a long overdue recast of a morphological phylogeny estimate of the Ophiuroidea taking into account latest insights on microstructural features of the arm skeleton. Our final estimate is based on a total of 45 ingroup taxa, including 41 recent species covering the full range of extant ophiuroid higher taxon diversity and 4 fossil species known from exceptionally preserved material, and the Lower Carboniferous Aganaster gregarius as the outgroup. A total of 130 characters were scored directly on specimens. The tree resulting from the Bayesian inference analysis of the full data matrix is reasonably well resolved and well supported, and refutes all previous classifications, with most traditional families discredited as poly- or paraphyletic. In contrast, our tree agrees remarkably well with the latest molecular estimate, thus paving the way towards an integrated new classification of the Ophiuroidea. Among the characters which were qualitatively found to accord best with our tree topology, we selected a list of potential synapomorphies for future formal clade definitions. Furthermore, an analysis with 13 of the ingroup taxa reduced to the lateral arm plate characters produced a tree which was essentially similar to the full dataset tree. This suggests that dissociated lateral arm plates can be analysed in combination with fully known taxa and thus effectively unlocks the extensive record of fossil lateral arm plates for phylogenetic estimates. Finally, the age and position within our tree implies that the ophiuroid crown-group had started to diversify by the Early Triassic.
蛇尾类系统学目前正处于动荡状态，最近的分子估计与基于形态学的传统分类法产生了根本性的冲突。在此，我们尝试对蛇尾纲的形态系统发育估计进行早就该进行的重塑，同时考虑到对腕骨微观结构特征的最新认识。我们的最终估计基于总共45个类群，包括41个现存物种，涵盖了现存蛇尾类高级分类单元的全部多样性，以及4个从保存异常完好的材料中得知的化石物种，还有下石炭统的群居阿加蛇尾作为外类群。总共130个特征直接在标本上进行了评分。对完整数据矩阵进行贝叶斯推断分析得到的树状图得到了较好的解析和有力支持，并且反驳了所有先前的分类，大多数传统科被证明是多系或并系的。相比之下，我们的树状图与最新的分子估计结果非常吻合，从而为蛇尾纲的综合新分类法铺平了道路。在定性发现与我们的树拓扑结构最相符的特征中，我们选择了一份潜在的共衍征清单，用于未来正式的分支定义。此外，对13个类群进行简化，仅保留侧腕板特征的分析产生了一棵与完整数据集树状图基本相似的树。这表明解离的侧腕板可以与完全已知的类群结合进行分析，从而有效地解锁大量的化石侧腕板记录用于系统发育估计。最后，我们树状图中的年代和位置意味着蛇尾类冠群在早三叠世就已开始分化。
