Dicynodont therapsids were a major component of the Permo‐Triassic terrestrial ecosystems across Pangea and have been regarded as specialized herbivores. In South America, the group was represented by several taxa of the clade Kannemeyeriiformes spanning from the Middle to the Late Triassic. In order to evaluate if cranial differences among taxa are potentially related to differences in feeding function, we performed a geometric morphometric analysis on 28 South American dicynodont crania. We digitized 19 cranial landmarks and conducted generalized Procrustes analysis, principal component analysis (PCA), principal component analysis between groups (bg‐PCA), and a branch weighted squared‐change parsimony approach. Phylogenetic inertia was not a significant driver of cranial shape evolution in the group, whereas PCA and bg‐PCA support that major morphological shape differences are concentrated in the preorbital region (relative length of the snout and width of the caniniform process), in the position of quadrate condyle in relation to the caniniform process, and in the increase in the intertemporal surface area. In this context, tusked Dinodontosaurus, “Kannemeyeria,” and Vinceria have relatively smaller adductor attachment areas and input moment arm than younger taxa lacking tusks, such as Ischigualastia, Stahleckeria, and Jachaleria. Differences in cranial morphology in later dicynodonts reflect modifications in feeding mechanics, probably due to changes in food resources (vegetation) in their habitats toward the end of the Triassic.

中文翻译：

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一种分析南美洲三叠纪二齿兽类（Therapsida，Anomodontia）头骨形状的几何形态测量方法

Dicynodont therapsids 是整个盘古大陆二叠纪-三叠纪陆地生态系统的主要组成部分，被认为是专门的食草动物。在南美洲，该群体的代表是从中三叠世到晚三叠世的 Kannemeyeriiformes 进化枝的几个分类群。为了评估分类群之间的颅骨差异是否可能与摄食功能的差异有关，我们对 28 只南美二齿兽类颅骨进行了几何形态测量分析。我们将 19 个颅骨标志数字化，并进行了广义 Procrustes 分析、主成分分析 (PCA)、组间主成分分析 (bg-PCA) 和分支加权平方变化简约方法。系统发育惰性不是该组颅骨形状进化的重要驱动因素，而 PCA 和 bg-PCA 支持主要的形态学形状差异集中在眶前区域（口鼻部的相对长度和犬突的宽度）、方形髁相对于犬突的位置，以及跨期表面积。在这种情况下，长牙的恐龙龙、“Kannemeyeria”和 Vinceria 的内收肌附着区域和输入力臂比缺乏象牙的年轻分类群（如 Ischigualastia、Stahleckeria 和 Jachaleria）相对较小。后期二齿兽类颅骨形态的差异反映了摄食机制的变化，这可能是由于三叠纪末期它们栖息地的食物资源（植被）发生了变化。