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。鉴于复杂性状的演化重新获得现象看似极为罕见，学界据此提出了多洛定律（Dollo’s Law）：复杂性状一旦丢失，便至少无法通过完全一致的演化过程再次演化形成。本研究开展了迄今针对有鳞目（Squamata）躯体形态演化最为全面且精细的分析之一，并引入了一类亲缘关系紧密、形态变异丰富的蜥蜴作为全新的模式系统。我们的系统发育分析结果证实，存在多起独立的完全肢体丢失事件，同时也存在多起指（趾）与外耳孔的丢失及重新获得案例。更为引人注目的是，本研究获得了强有力的统计学证据，证明从指（趾）数目减少的祖先类群中，可以重新演化出五趾型（pentadactyl）躯体构型。本研究发现，短腿蜥属（Brachymeles）的物种占据了有鳞目中此前未被记录过的形态空间（morphospace）区域，即躯体构型（body plans）。本研究结果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：无论是何种演化约束塑造了其他有鳞类群（双足蚓蜥属Bipes除外）的形态演化趋势，这类约束在这一极具代表性的演化支（clade）中均已消失。本研究结果与新兴研究文献形成呼应，这些文献均通过强有力的统计学证据证实了复杂性状的丢失，以及随后演化重新获得与广义五趾型躯体构型相关的复杂结构的现象。