Burrowing is one of the many locomotor modes of frogs (order Anura) and is found within many clades. Burrowing is generally categorized into two groups: forward-burrowing and backward-burrowing. While forward-burrowing is more rare than backward-burrowing, we show that it has evolved independently at least eight times across anurans and is correlated with distinct features of the external and internal anatomy. The shape of the humerus is especially important for forward-burrowing, as many species use their forelimbs for digging. Using X-ray computed tomography data, we characterize shape variation in the humerus, including three-dimensional (3D) morphometrics, assess the morphology of muscles related to this variation in the humerus, and discuss the mechanical and evolutionary consequences of our results. We show that the humeri of most forward-burrowing frogs are morphologically distinct from those of non-forward-burrowers, including features such as a curved and thick diaphysis, the presence of a pronounced ventral crest, and relatively large epicondyles and humeral head. Our findings also suggest that pectoral muscle anatomy differs substantially among burrowing modes in frogs. This work provides a framework for predicting locomotor modes in taxa for which the natural history is poorly known as well as extinct taxa.

中文翻译：

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前挖青蛙的肱骨比较形态

挖洞是青蛙的许多运动方式之一（安努拉（Anura）），在许多进化枝中都可以找到。挖掘通常分为两类：前向挖掘和后向挖掘。尽管前向掘进比向后掘进更为罕见，但我们证明了它在整个无核动物中至少独立进化了八次，并且与外部和内部解剖结构的独特特征相关。肱骨的形状对于向前挖掘尤为重要，因为许多物种都使用其前肢进行挖掘。使用X射线计算机断层扫描数据，我们可以表征肱骨的形状变化，包括三维（3D）形态计量学，评估与肱骨这种变化相关的肌肉形态，并讨论结果的力学和进化结果。我们显示，大多数向前穴居青蛙的肱骨在形态上与非向前穴居青蛙不同，包括弯曲而粗大的骨干，明显的腹rest以及相对较大的上con和肱骨头等特征。我们的发现还表明，在青蛙的穴位模式之间，胸肌的解剖结构存在很大差异。这项工作提供了一个框架，用于预测自然史以及已灭绝的生物分类群中的运动模式。我们的发现还表明，在青蛙的穴位模式之间，胸肌的解剖结构存在很大差异。这项工作提供了一个框架，用于预测自然史以及已灭绝的生物分类群中的运动模式。我们的发现还表明，在青蛙的穴位模式之间，胸肌的解剖结构存在很大差异。这项工作提供了一个框架，用于预测自然史以及已灭绝的生物分类群中的运动模式。