Evolution of The Hallux in Non-Avian Theropod Dinosaurs
Evolution of The Hallux in Non-Avian Theropod Dinosaurs
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DOI：
10.1080/02724634.2016.1116995
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发表时间：
2016-03
影响因子：
1.4
通讯作者：
Soki Hattori
中科院分区：
文献类型：
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作者：
Soki Hattori
摘要兽脚亚目恐龙谱系中反向趾（第一足趾）的出现被认为是抓握能力增强和可能树栖性的重要指标。然而，在非鸟类兽脚亚目动物中，除了在站立阶段支持和推动身体的主要作用外，具有近形、非反向拇趾的足跖的功能还没有得到充分的解决。为了阐明拇功能，在这项研究中，21个标本的非鸟类兽脚类动物进行了检查。在腹足类中，第一跖骨的近端与现存鳄鱼一样到达踝关节。第一跖骨的大小，然后减少，失去了与踝关节的直接接触，并转移更多的plantarily在基础neotheropods。在有关节的腔骨标本中，第一跖骨的近端附着于第二跖骨的足底内侧边缘，而第一跖骨的远端和拇趾位于足的足底面。在4个有关节的驰龙科速龙标本中，第一跖骨在第二跖骨上的保存位置从内侧到足底各不相同，相应地，在其远端关节处的伸展/屈曲运动的旋转轴范围从内侧到背跖。在伤齿龙类的标本中也观察到了类似的情况，这表明恐爪龙类第一跖骨的近端关节面与现存鸟类相似，从而使第一和第二跖骨之间存在跖骨间活动。
ABSTRACT The emergence of a reversed hallux (first pedal digit) in the theropod lineage is regarded as an important indicator of increasing grasping ability and possibly arboreality. However, functions of the pes with a plesiomorphic, nonreversed hallux in non-avian theropods, other than the major role in supporting and propelling the body during the stance phase, have not been fully addressed. To clarify hallucal function, 21 specimens of non-avian theropods were examined in this study. Ancestrally in Theropoda, the proximal end of the first metatarsal reached the ankle joint as in extant crocodilians. The size of the first metatarsal was then reduced, lost direct contact with the ankle joint, and shifted more plantarly in basal neotheropods. In articulated coelophysoid specimens, the proximal end of the first metatarsal attaches to the medioplantar margin of the second metatarsal, whereas the distal part of the first metatarsal and phalanges of the hallux lies on the plantar aspect of the pes. In four articulated specimens of the dromaeosaurid Velociraptor, preserved positions of the first metatarsal on the second metatarsal vary from the medial to plantar aspects, and correspondingly the rotational axis of the extension/flexion movement at its distal articulation ranges from mediolateral to dorsoplantar. Similar conditions are also observed in troodontid specimens, suggesting the presence of intermetatarsal mobility between the first and second metatarsals enabled by a convex proximal articular surface of the first metatarsal in deinonychosaurians similar to the one present in extant birds.