Birds can use different types of gaits to move on the ground: they either walk, hop, or run. Although velocity can easily explain a preference for running, it remains unclear what drives a bird species to favour hopping over walking. As many hopping birds are relatively small and arboreal, we wanted to test the link between size, arboreality and hopping ability. First, we carried out ancestral character state reconstructions of size range, hopping ability and habitat traits on over 1000 species of birds. We found that both hopping ability and arboreality were derived and significantly correlated traits in avian evolution. Second, we tested the influence of hopping ability on the morphology of the lower appendicular skeleton by quantifying the shape differences of the pelvis and the three long bones of the hind limbs in 47 avian species with different habitats and gait preferences. We used geometric morphometrics on 3D landmarks, digitized on micro-CT and surface scans of the pelvis, femur, tibiotarsus, and tarsometatarsus. Locomotion habits significantly influence the conformation of the pelvis, especially at the origin of hip and knee muscle extensors. Interestingly, habitat, more than locomotion habits, significantly changed tarsometatarsus conformation. The morphology of the distal part of the tarsometatarsus constrains digit orientation, which leads to a greater ability to perch, an advantageous trait in arboreality. The results of this work suggest an arboreal origin of hopping and illuminate the evolution of avian terrestrial locomotion.

中文翻译：

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跳还是不跳？答案在鸟树中

鸟类可以使用不同类型的步态在地面上移动：它们可以走路、跳跃或奔跑。尽管速度可以很容易地解释对跑步的偏好，但目前尚不清楚是什么驱使鸟类更喜欢跳跃而不是步行。由于许多跳跃的鸟类相对较小且栖息在树上，因此我们想测试大小、树栖性和跳跃能力之间的联系。首先，我们对1000多种鸟类进行了大小范围、跳跃能力和栖息地特征的祖先特征状态重建。我们发现，在鸟类进化中，跳跃能力和树栖性都是衍生的，并且与性状显着相关。第二，我们通过量化具有不同栖息地和步态偏好的 47 种鸟类的骨盆和后肢的三个长骨的形状差异，测试了跳跃能力对下附肢骨骼形态的影响。我们在 3D 地标上使用几何形态测量学，在骨盆、股骨、胫骨和跗跖骨的显微 CT 和表面扫描上进行数字化。运动习惯显着影响骨盆的构造，尤其是在髋部和膝部肌肉伸肌的起点。有趣的是，栖息地，而不是运动习惯，显着改变了跗跖骨的构造。跗跖骨远端的形态限制了手指的方向，这导致了更大的栖息能力，这是树栖的一个有利特征。