Didelphid marsupials are considered a morphologically unspecialized group with a generalist diet that includes vertebrates, invertebrates, and plant matter. While cranium and scapula variation has already been examined within Didelphidae, variation in mandible shape, usually associated with diet or phylogeny in other mammalian groups, has not yet been properly assessed in the family. We evaluated the variation in mandible shape and size of didelphids (2470 specimens belonging to 94 species) using 2D geometric morphometrics. We classified the diet of the didelphids into four broad categories to assess whether morphospace ordination relates to dietary habits. We also provided the most comprehensive phylogeny for the family (123 out of the 126 living species) using 10 nuclear and mitochondrial genes. We then mapped mandible size and shape onto that phylogeny for 93 selected taxa and ancestral size and shapes were reconstructed by parsimony. We found phylogenetically structured variation in mandible morphology between didelphid groups, and our results indicate that they have a significant phylogenetic signal. The main axis of shape variation is poorly related to size, but the second is strongly allometric, indicating that allometry is not the main factor in shaping morphological diversity on their mandibles. Our results indicate that the shape and size of the ancestral mandible of didelphids would be similar to that of the current species of the genus Marmosa.

中文翻译：

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负鼠下颌骨的进化、分歧和趋同（Didelphidae、Didelphimorphia）

双翅目有袋动物被认为是形态上非特化的类群，其饮食包括脊椎动物、无脊椎动物和植物。虽然颅骨和肩胛骨的变异已经在双齿科中得到了研究，但下颌骨形状的变异通常与其他哺乳动物群体的饮食或系统发育有关，但尚未在该科中得到适当的评估。我们使用 2D 几何形态测量学评估了双海豚（属于 94 个物种的 2470 个标本）下颌骨形状和大小的变化。我们将双海豚的饮食分为四大类，以评估形态空间排序是否与饮食习惯相关。我们还使用 10 个核和线粒体基因提供了该科（126 个现存物种中的 123 个）最全面的系统发育。然后，我们将下颌骨的大小和形状映射到 93 个选定分类群的系统发育上，并通过简约法重建祖先的大小和形状。我们发现双齿类群体之间下颌骨形态存在系统发育结构变异，我们的结果表明它们具有显着的系统发育信号。形状变异的主轴与大小关系不大，但第二个是强烈的异速生长，表明异速生长并不是塑造下颌骨形态多样性的主要因素。我们的研究结果表明，双海豚祖先下颌骨的形状和大小与目前马尔莫萨属物种的下颌骨相似。我们的结果表明它们具有显着的系统发育信号。形状变异的主轴与大小关系不大，但第二个是强烈的异速生长，表明异速生长并不是塑造下颌骨形态多样性的主要因素。我们的研究结果表明，双海豚祖先下颌骨的形状和大小与目前马尔莫萨属物种的下颌骨相似。我们的结果表明它们具有显着的系统发育信号。形状变异的主轴与大小关系不大，但第二个是强烈的异速生长，表明异速生长并不是塑造下颌骨形态多样性的主要因素。我们的研究结果表明，双海豚祖先下颌骨的形状和大小与目前马尔莫萨属物种的下颌骨相似。