Background There are limited data on intra- and interspecific osteological variation for many squamate clades. Those data are relevant for phylogenetic analyses that use osteological characters and for apomorphic identifications of fossils. We investigate whether morphological features in the skulls of extant gerrhonotine lizards can be used to distinguish taxa at the species- and genus-level and assess whether newly discovered intra- and interspecific osteological variation alters the utility of previously reported apomorphic features. We examined skulls of species belonging to the gerrhonotine genera Elgaria and Gerrhonotus. These genera contain 17 extant species, but the cranial osteology of only a few species was previously examined. As a result, intra- and interspecific osteological variation of these gerrhonotines is poorly understood. Methods We employed high-resolution x-ray computed tomography (CT) to scan 25 alcohol-preserved specimens. We provide data on the skulls of all eight species of Elgaria, four for the first time, and five species of Gerrhonotus, three for the first time. We examined 3-D reconstructed skulls of the scanned specimens as well as dry, traditionally prepared skeletons (when they were available). Results We found that the purported diagnostic utility of many previously described morphological features is impacted because of substantial morphological variation between and within species. We present an assessment of osteological differences that may be useful to differentiate species of Elgaria and Gerrhonotus, many of which are present on isolated cranial elements commonly recovered as fossils, including the premaxilla, maxilla, parietal, pterygoid, prootic, dentary, and surangular. We demonstrate the importance of documenting patterns of osteological variation using large sample sizes, and the utility of examining disarticulated cranial elements of the squamate skull to identify diagnostic morphology. This study adds to a growing body of literature suggesting that extensive documentation of morphological variation is needed to further our understanding of the phylogenetic and diagnostic utility of morphological features across vertebrate clades. Efforts in that direction likely will benefit from examination of disarticulated skeletal elements.

中文翻译：

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Elgaria 和 Gerrhonotus (Anguidae, Gerrhonotinae) 头骨的变异及其对系统发育和化石鉴定的意义

背景 关于许多鳞状进化枝的种内和种间骨学变异的数据有限。这些数据与使用骨学特征的系统发育分析和化石的变形鉴定相关。我们调查现存gerrhonotine 蜥蜴头骨的形态特征是否可用于区分物种和属水平的分类群，并评估新发现的种内和种间骨学变异是否会改变先前报道的无形特征的效用。我们检查了属于 gerrhonotine 属 Elgaria 和 Gerrhonotus 的物种的头骨。这些属包含 17 个现存物种，但以前只检查了少数物种的颅骨学。因此，对这些gerrhonotines 的种内和种间骨学变异知之甚少。方法 我们采用高分辨率 X 射线计算机断层扫描 (CT) 扫描 25 个酒精保存标本。我们提供了所有八种 Elgaria 头骨的数据，其中四种是首次，还有五种 Gerrhonotus 的头骨数据，三种是首次。我们检查了扫描标本的 3-D 重建头骨以及干燥的、传统制备的骨骼（当它们可用时）。结果我们发现，许多先前描述的形态特征的所谓诊断效用受到影响，因为物种之间和物种内部存在大量的形态变化。我们对可能有助于区分 Elgaria 和 Gerrhonotus 物种的骨学差异进行评估，其中许多存在于通常作为化石回收的孤立颅骨元素上，包括前上颌骨、上颌骨、顶叶、翼状骨、prootic、denary 和 surangular。我们证明了使用大样本量记录骨学变异模式的重要性，以及检查鳞状颅骨的脱节颅骨元素以识别诊断形态的实用性。这项研究增加了越来越多的文献，表明需要对形态变异进行大量记录，以进一步了解脊椎动物进化枝形态特征的系统发育和诊断效用。在这个方向上的努力可能会受益于对脱节骨骼元素的检查。这项研究增加了越来越多的文献，表明需要对形态变异进行大量记录，以进一步了解脊椎动物进化枝形态特征的系统发育和诊断效用。在这个方向上的努力可能会受益于对脱节骨骼元素的检查。这项研究增加了越来越多的文献，表明需要对形态变异进行大量记录，以进一步了解脊椎动物进化枝形态特征的系统发育和诊断效用。在这个方向上的努力可能会受益于对脱节骨骼元素的检查。