Echimyidae is a species‐rich clade of Neotropical rodents, which diversified in association with forested biomes. Since the late Miocene, a few lineages from southern South America have been adapted to open environments. Eumysops is one of these southern echimyids, and its peculiar craniomandibular morphology has been assumed to be a result of adaptation to open environments. We performed a geometric morphometric analysis of craniomandibular shape variation to explore whether, as suspected, Eumysops is divergent from other echimyids and octodontoids. In addition, we explored whether deterministic factors driven by different ecological dimensions can explain the diversification of shape among octodontoids. We found that craniomandibular shape variation in octodontoids was related to ecological variables. Comparing competing evolutionary models suggested that the input of selective factors play a key role in octodontoid craniomandibular shape diversification; habitat and habits were found to be the most influential factors. In the analysed morphospaces, Eumysops was located distant from other echimyids due to its distinctive traits, especially wide and posteriorly displaced orbits, and related low craniomandibular joint. Divergent orbits and resulting wider panoramic vision support the interpretation of Eumysops as an open‐habitat specialist echimyid. But what is more relevant, is that Eumysops occupied a sector of the octodontoid cranial morphospace not filled by living representatives; this highlights the contribution of fossils in providing key information on the specialization boundaries explored by a clade throughout its history.

中文翻译：

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在南美八齿类啮齿动物（Hystricomorpha）的进化环境中揭示上新世更新世Eymysops独特的颅颌下形态。

棘科是新热带啮齿动物的一个物种丰富的进化枝，随着森林生物群落的发展而多样化。自中新世晚期以来，南美南部的一些血统已经适应了开放环境。Eumysops是这些南部的棘皮动物之一，其奇特的颅颌下颌形态被认为是适应开放环境的结果。我们进行了颅下颌形状变化的几何形态计量学分析，以探索是否怀疑Eumysops与其他棘皮动物和八突类动物不同。此外，我们探讨了由不同生态维度驱动的确定性因素是否可以解释八齿类动物体形的多样性。我们发现八齿类动物的颅下颌形状变化与生态变量有关。比较竞争性进化模型表明，选择因子的输入在八齿颌颅下颌形状多样化中起关键作用。发现栖息地和习惯是最有影响力的因素。在所分析的形态空间中，Eyyopops因其独特的特征（尤其是宽且向后移位的轨道）和相关的低颌下颌关节而与其他棘皮动物相距较远。发散的轨道和由此产生的更广阔的全景视野支持对Eumysops是一种开放式栖居性棘皮动物。但更重要的是，Eymysops占据了八角形颅骨形态空间的一部分，而活着的代表却没有填充它；这突出了化石在提供关于进化枝在其整个历史中探索的专业化领域的关键信息方面的贡献。