Data from: Evidence for repeated acquisition and loss of complex body form characters in an insular clade of Southeast Asian semi-fossorial skinks

Evolutionary simplification, or loss of complex characters, is a major theme in studies of body form evolution. The apparently infrequent evolutionary reacquisition of complex characters has led to the assertion (Dollo’s Law) that once lost, complex characters may be impossible to re-evolve, at least via the exact same evolutionary process. Here we provide one of the most comprehensive, fine-scale analyses of squamate body-form evolution to date, introducing a new model system of closely related, morphologically variable, lizards. Our phylogenetic results support independent instances of complete limb loss as well as multiple instances of digit and external ear opening loss and re-acquisition. Even more striking, we find strong statistical support for the re-acquisition of a pentadactyl body form from a digit-reduced ancestor. Our study reveals that species of the genus Brachymeles exemplify regions of morphospace (body plans) previously undocumented in squamates. Our findings have broad, general implications for body form evolution in burrowing vertebrates: whatever constraints have shaped trends in morphological evolution among other squamate groups (excluding Bipes) have been lost in this one exemplary clade. The results of our study join a nascent body of literature showing strong statistical support for complex character loss, followed by evolutionary re-acquisition of complex structures associated with a generalized pentadactyl body form.

演化简化，即复杂性状的丢失，是躯体形态演化研究中的核心主题之一。复杂性状的演化复现现象看似极为罕见，由此催生了多洛氏不可逆法则（Dollo’s Law）的提出：复杂性状一旦丢失，便几乎不可能通过完全相同的演化路径再次演化形成，至少在常规情形下如此。本研究开展了目前为止针对有鳞目（squamate）躯体形态演化最为全面且精细的分析之一，引入了一组亲缘关系紧密、形态变异丰富的蜥蜴作为全新的模式研究系统。我们的系统发育分析结果证实，肢体完全丢失存在多次独立演化事件，同时还存在多起趾数与外耳孔的丢失及复现事件。更为引人注目的是，我们的分析得到了强有力的统计学支持，证明五指型躯体形态可从趾数减少的祖先类群中重新演化而来。本研究揭示，短肢蜥属（Brachymeles）物种占据了此前有鳞目类群中未被记录过的形态空间（morphospace）。我们的发现对于穴居脊椎动物的躯体形态演化具有广泛的普适性启示：除双足蜥属（Bipes）外，其他有鳞目类群所受的形态演化约束，在这一极具代表性的演化支中已然消失。本研究结果与新兴学术文献的结论相呼应，后者通过强有力的统计学证据证实，复杂性状可发生丢失，随后可演化复现与典型五指型躯体形态相关的复杂结构。