UMR 7207 du CNRS, Département Histoire de la Terre, Muséum National d'Histoire Naturelle, Paris, France.
J Anat. 2010 Dec;217(6):715-27. doi: 10.1111/j.1469-7580.2010.01307.x. Epub 2010 Oct 12.
The histological study of vertebrae in extant squamates shows that the internal vertebral structure in this group differs from that of other tetrapods. Squamate vertebrae are lightly built and basically composed of two roughly concentric osseous tubes--one surrounding the neural canal and the other constituting the peripheral cortex of the vertebra--connected by few thin trabeculae. This structure, which characteristically evokes that of a tubular bone, results from a peculiar remodelling process characterised by an imbalance between local bone resorption and redeposition; in both periosteal and endosteo-endochondral territories, bone is extensively resorbed but not reconstructed in the same proportion by secondary deposits. This process is particularly intense in the deep region of the centrum, where originally compact cortices are made cancellous, and where the endochondral spongiosa is very loose. This remodelling process starts at an early stage of development and remains active throughout subsequent growth. The growth of squamate centra is also strongly asymmetrical, with the posterior (condylar) part growing much faster than the anterior (cotylar) part. Preliminary analyses testing for associations between vertebral structure and habitat use suggest that vertebrae of fossorial taxa are denser than those of terrestrial taxa, those in aquatic taxa being of intermediate density. However, phylogenetically informed analyses do not corroborate these findings, thus suggesting a strong phylogenetic signal in the data. As our analyses demonstrate that vertebrae in snakes are generally denser than those of lizards sensu stricto, this may drive the presence of a phylogenetic signal in the data. More comprehensive sampling of fossorial and aquatic lizards is clearly needed to more rigorously evaluate these patterns.
对现存蜥蜴类的脊椎骨组织学研究表明，该类群的内部脊椎结构与其他四足动物不同。蜥蜴类的脊椎骨结构较轻，基本由两个大致同心的管状骨组成——一个围绕神经管，另一个构成脊椎的外周皮质——由少量薄的骨小梁连接。这种结构的特点是类似于管状骨，这是由于一种特殊的重塑过程所致，该过程的特征是局部骨吸收和再沉积之间的不平衡；在骨膜和内骨-软骨内区域，骨广泛吸收，但不能以相同的比例通过次级沉积重建。这个过程在椎体的深部区域尤为强烈，原本致密的皮质变得松质化，软骨内海绵骨非常疏松。这个重塑过程在发育的早期开始，并在随后的生长过程中保持活跃。蜥蜴类椎体的生长也是强烈不对称的，后部（髁）比前部（关节窝）生长得快得多。初步分析测试了脊椎结构与栖息地利用之间的关联，结果表明，穴居类群的椎体比陆生类群的椎体密度更大，而水生类群的椎体密度居中。然而，基于系统发育的分析并不能证实这些发现，因此表明数据中存在强烈的系统发育信号。由于我们的分析表明，蛇类的椎体通常比严格意义上的蜥蜴类的椎体密度更大，这可能导致数据中存在系统发育信号。显然需要更全面地采样穴居和水生蜥蜴，以更严格地评估这些模式。
