Among vertebrates, placental mammals are particularly variable in the covariance between cranial shape and body size (allometry), with rodents being a major exception. Australian murid rodents allow an assessment of the cause of this anomaly because they radiated on an ecologically diverse continent notably lacking other terrestrial placentals. Here, we use 3D geometric morphometrics to quantify species-level and evolutionary allometries in 38 species (317 crania) from all Australian murid genera. We ask whether ecological opportunity resulted in greater allometric diversity compared with other rodents or whether conserved allometry suggests intrinsic constraints and/or stabilizing selection. We also assess whether cranial shape variation follows the proposed rule of craniofacial evolutionary allometry (CREA), whereby larger species have relatively longer snouts and smaller braincases. To ensure we could differentiate parallel versus nonparallel species-level allometric slopes, we compared the slopes of rarefied samples across all clades. We found exceedingly conserved allometry and CREA-like patterns across the 10-million-year split between Mus and Australian murids. This could support both intrinsic-constraint and stabilizing-selection hypotheses for conserved allometry. Large-bodied frugivores evolved faster than other species along the allometric trajectory, which could suggest stabilizing selection on the shape of the masticatory apparatus as body size changes.

中文翻译：

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澳大利亚啮齿动物揭示了1000万年Murid进化过程中保守的颅骨进化变态。

在脊椎动物中，胎盘哺乳动物的颅骨形状和体型之间的协方差尤其可变（异位症），其中啮齿类动物是一个主要例外。澳大利亚鼠类啮齿动物可以评估这种异常的原因，因为它们辐射在生态多样的大陆上，特别是缺少其他陆地胎盘。在这里，我们使用3D几何形态计量学来量化来自澳大利亚全部穆属的38个物种（317克罗尼亚）的物种水平和进化异构。我们询问与其他啮齿动物相比，生态机会是否会导致更大的异体异形多样性，或者保守异体异形是否暗示内在约束和/或稳定选择。我们还评估了颅骨形状变化是否遵循颅面进化变构法（CREA）的拟议规则，因此，较大的物种具有相对较长的鼻子和较小的脑袋。为了确保我们可以区分平行和非平行物种水平的异形斜率，我们比较了所有进化枝中稀有样品的斜率。我们发现，在1000万年之间，穆斯和澳大利亚混血儿。这可以支持内在约束的内在约束和稳定选择假设。大体上的节食动物沿着异体异形的轨迹进化得比其他物种快，这可能表明随着体型的变化，咀嚼器形状的选择稳定。