Camaiti Marco, Evans Alistair R, Hipsley Christy A, Chapple David G
School of Biological Sciences, Monash University, 19 Rainforest Walk, Clayton, VIC, 3800, Australia.
School of BioSciences, The University of Melbourne, Parkville, VIC, 3010, Australia.
Biol Rev Camb Philos Soc. 2021 Jun;96(3):1035-1050. doi: 10.1111/brv.12690. Epub 2021 Feb 3.
Elongated snake-like bodies associated with limb reduction have evolved multiple times throughout vertebrate history. Limb-reduced squamates (lizards and snakes) account for the vast majority of these morphological transformations, and thus have great potential for revealing macroevolutionary transitions and modes of body-shape transformation. Here we present a comprehensive review on limb reduction, in which we examine and discuss research on these dramatic morphological transitions. Historically, there have been several approaches to the study of squamate limb reduction: (i) definitions of general anatomical principles of snake-like body shapes, expressed as varying relationships between body parts and morphometric measurements; (ii) framing of limb reduction from an evolutionary perspective using morphological comparisons; (iii) defining developmental mechanisms involved in the ontogeny of limb-reduced forms, and their genetic basis; (iv) reconstructions of the evolutionary history of limb-reduced lineages using phylogenetic comparative methods; (v) studies of functional and biomechanical aspects of limb-reduced body shapes; and (vi) studies of ecological and biogeographical correlates of limb reduction. For each of these approaches, we highlight their importance in advancing our understanding, as well as their weaknesses and limitations. Lastly, we provide suggestions to stimulate further studies, in which we underscore the necessity of widening the scope of analyses, and of bringing together different perspectives in order to understand better these morphological transitions and their evolution. In particular, we emphasise the importance of investigating and comparing the internal morphology of limb-reduced lizards in contrast to external morphology, which will be the first step in gaining a deeper insight into body-shape variation.
在脊椎动物的进化历程中，与肢体退化相关的细长蛇形身体已经多次进化出现。肢体退化的有鳞目动物（蜥蜴和蛇）占据了这些形态转变的绝大部分，因此在揭示宏观进化转变和体型转变模式方面具有巨大潜力。在此，我们对肢体退化进行全面综述，审视并讨论关于这些显著形态转变的研究。从历史角度来看，研究有鳞目动物肢体退化有几种方法：（i）定义蛇形身体形状的一般解剖学原理，以身体各部分与形态测量之间的不同关系来表示；（ii）从进化角度利用形态比较来构建肢体退化的框架；（iii）确定参与肢体退化形态个体发育的发育机制及其遗传基础；（iv）使用系统发育比较方法重建肢体退化谱系的进化历史；（v）研究肢体退化体型的功能和生物力学方面；以及（vi）研究肢体退化的生态和生物地理相关性。对于这些方法中的每一种，我们都强调它们在推进我们的理解方面的重要性，以及它们的弱点和局限性。最后，我们提出建议以激发进一步的研究，其中我们强调扩大分析范围以及汇集不同观点以更好地理解这些形态转变及其进化的必要性。特别是，我们强调研究和比较肢体退化蜥蜴的内部形态与外部形态的重要性，这将是更深入了解体型变异的第一步。
