音调变形,地质过程导致的化石变形,在解决古生物学问题时使用几何形态计量学存在问题。来自生物变异的信号,比如个体发育趋势和性二态,如果变形的变化太高,可能会丢失。这里,我们研究了植物变形对丰富的几何形态计量学分析的影响,著名的二叠纪疗法Diictodonfeliceps。扭曲的Diictodoncrania可以分为七个典型的变形方式:横向压缩,背侧腹侧压迫,前后受压,“鞍形”变形(颅骨中段局部塌陷),前背剪切,正腹切变,和右/左剪切。在包含已知“生物”信号并经受均匀剪切的模拟形态测量数据集中,变形通常是方差的主要来源,但在大多数情况下可以恢复准确的“生物”信息。然而,在经验数据集中,变形不仅是方差的主要来源,但是与异速异形和性二态性相关的结构很少,这表明,实际化石套印生物变异所遭受的变形样式更加多样化。在所有非模型疗法的主成分分析中,变形的Diictodon标本在基于未变形标本的形态空间中,在该分类单元的“真实”位置周围表现出明显的分散。与牙齿畸形整体变形相关的总体差异很小,研究样本中的主要变异轴显示出强烈的系统发育信号。尽管在较低的分类水平上研究化石类群的变异非常有问题,本研究中变形的累积效应是随机的,并且在形态学差异的更高水平分析中包含变形的标本是必要的。发现扭曲标本的平均形态近似于未扭曲标本的形态,因此,我们建议在可能的情况下在更高级别的分析中使用物种级别的方法。
Taphonomic deformation, the distortion of fossils as a result of geological processes, poses problems for the use of geometric morphometrics in addressing paleobiological questions. Signal from biological variation, such as ontogenetic trends and sexual dimorphism, may be lost if variation from deformation is too high. Here, we investigate the effects of taphonomic deformation on geometric morphometric analyses of the abundant, well known Permian therapsid Diictodon feliceps. Distorted Diictodon crania can be categorized into seven typical styles of deformation: lateral compression, dorsoventral compression, anteroposterior compression, \"saddle-shape\" deformation (localized collapse at cranial mid-length), anterodorsal shear, anteroventral shear, and right/left shear. In simulated morphometric datasets incorporating known \"biological\" signals and subjected to uniform shear, deformation was typically the main source of variance but accurate \"biological\" information could be recovered in most cases. However, in empirical datasets, not only was deformation the dominant source of variance, but little structure associated with allometry and sexual dimorphism was apparent, suggesting that the more varied deformation styles suffered by actual fossils overprint biological variation. In a principal component analysis of all anomodont therapsids, deformed Diictodon specimens exhibit significant dispersion around the \"true\" position of this taxon in morphospace based on undistorted specimens. The overall variance associated with deformation for Anomodontia as a whole is minor, and the major axes of variation in the
study sample show a strong phylogenetic signal instead. Although extremely problematic for studying variation in fossil taxa at lower taxonomic levels, the cumulative effects of deformation in this
study are shown to be random, and inclusion of deformed specimens in higher-level analyses of morphological disparity are warranted. Mean morphologies of distorted specimens are found to approximate the morphology of undistorted specimens, so we recommend use of species-level means in higher-level analyses when possible.