The origin of extant amphibians has been studied using several sources of data and methods, including phylogenetic analyses of morphological data, molecular dating, stratigraphic data, and integration of ossification sequence data, but a consensus about their affinities with other Paleozoic tetrapods has failed to emerge. We have compiled five datasets to assess the relative support for six competing hypotheses about the origin of extant amphibians: a monophyletic origin among temnospondyls, a monophyletic origin among lepospondyls, a diphyletic origin among both temnospondyls and lepospondyls, a diphyletic origin among temnospondyls alone, and two variants of a triphyletic origin, in which anurans and urodeles come from different temnospondyl taxa while caecilians come from lepospondyls and are either closer to anurans and urodeles or to amniotes. Our datasets comprise ossification sequences of up to 107 terminal taxa and up to eight cranial bones, and up to 65 terminal taxa and up to seven appendicular bones, respectively. Among extinct taxa, only two or three temnospondyl can be analyzed simultaneously for cranial data, but this is not an insuperable problem because each of the six tested hypotheses implies a different position of temnospondyls and caecilians relative to other sampled taxa. For appendicular data, more extinct taxa can be analyzed, including some lepospondyls and the finned tetrapodomorph Eusthenopteron, in addition to temnospondyls. The data are analyzed through maximum likelihood, and the AICc (corrected Akaike Information Criterion) weights of the six hypotheses allow us to assess their relative support. By an unexpectedly large margin, our analyses of the cranial data support a monophyletic origin among lepospondyls; a monophyletic origin among temnospondyls, the current near-consensus, is a distant second. All other hypotheses are exceedingly unlikely according to our data. Surprisingly, analysis of the appendicular data supports triphyly of extant amphibians within a clade that unites lepospondyls and temnospondyls, contrary to all phylogenies based on molecular data and recent trees based on paleontological data, but this conclusion is not very robust.

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关于现有两栖动物的起源，僵化序列告诉我们什么？

现有的两栖动物的起源已使用多种数据和方法来源进行了研究，包括形态数据，分子测年，地层学数据和骨化序列数据的整合的系统发育分析，但是关于它们与其他古生代四足动物的亲缘关系尚未达成共识。我们已经收集了五个数据集，以评估关于现存两栖动物起源的六个竞争假设的相对支持：temponspondyls中的单系起源，lepospondyls中的单系起源，temnospondyls和lepospondyls之间的双系起源，仅temnospondyls中的双系起源，以及三系起源的两个变体，其中无核小动物和urodeles来自不同的temponspondyl单元，而caecilian来自小卵石，并且更接近anurans和urodeles或羊膜。我们的数据集包括最多107个末端分类单元和最多8个颅骨，最多65个末端分类单元和最多7个阑尾骨的骨化序列。在已灭绝的分类单元中，只能同时分析两个或三个替米pondyl的颅骨数据，但这不是一个不可克服的问题，因为六个被检验的假设中的每一个都暗示了替米pondyls和凯氏菌相对于其他采样分类单元的不同位置。对于附加数据，可以分析更多灭绝的类群，包括一些类脂小体和有鳍的四足纲 但这不是一个不可克服的问题，因为六个被检验的假设中的每一个都隐含了坦诺斯通和凯撒人相对于其他抽样分类单元的不同位置。对于附加数据，可以分析更多灭绝的类群，包括一些Leponpondyls和鳍四足纲 但这不是一个不可克服的问题，因为六个被检验的假设中的每一个都隐含了坦诺斯通和凯撒人相对于其他抽样分类单元的不同位置。对于附加数据，可以分析更多灭绝的类群，包括一些Leponpondyls和鳍四足纲Eusthenopteron，除了temponspondyls。通过最大似然分析数据，并通过六个假设的AICc（校正的Akaike信息准则）权重来评估它们的相对支持。出乎意料的是，我们对颅骨数据的分析支持了Leponpondyls中的单系起源。目前在近乎一致的坦索类动物中，单系起源是遥远的第二个。根据我们的数据，所有其他假设极不可能。出人意料的是，对附属数据的分析支持了将Leponpondyls和temnospondyls结合在一起的进化枝中现存的两栖动物的三倍表现，这与基于分子数据的所有系统发育和基于古生物学数据的最新树木相反，但该结论并不是很可靠。