Study of the origins of the terrestriality in hominoids viewed from functional morphology of the talar joint

本研究旨在阐明关于人类-非洲类人猿分支中陆地起源(S)的进化过程。为此，对中新世猿类的距骨关节进行了研究。使用CT扫描仪观察了活体类人距下关节在内翻-外翻过程中的运动，并研究了骨学和运动学之间的关系。测量了大领事、尼扬扎(P Nyanzae)(约19-18 Ma)和纳丘利猿(Nacholapithecus)(约15 Ma)以及8个活体类人猿跟骨后距关节面的三维形态。跟骨化石中距骨后小关节和关节面轴的比例呈原始类人型。然而，化石类人猿的距下后关节在足内、外翻以及背屈和足底屈曲过程中表现出一定程度的旋转和内收。这种类型的功能适应不同于活着的大板状…更多的鼻科动物，其中只有背屈和掌屈占主导地位。这些化石猿的后距骨小关节是独一无二的，因为小关节的后部和前部特别平坦，中间部分很好地弯曲或凸起。当足部不同程度地内翻或外翻时，距下后关节可能是完全足底屈曲或背屈的位置，关节面的后部在内侧表现出强烈的倾斜。这会导致与足底屈曲相关的更大的侧向旋转和/或内收。与这种情况不同的是，颈椎病的关节表面变短，导致关节的活动范围更小，关节更稳定。这一条件反映了原始脊椎动物的半陆地阶段。盘氏关节面中间部分凸度较小，光滑度低。关节面的长轴与跟骨轴呈强烈的夹角。这些特化通过不同的位置和内翻-外翻运动中的更大比例的旋转来增强关节的稳定性。跟骨化石具有广泛的翻转-外翻和高稳定性，在完全倒置的外翻位置上，尽管比现存的类人猿少，因此不太适合地面运动。潘所见的形态可能是从跟骨化石发展而来的。然而，它们之间存在陆地适应阶段(类似于尾虫的形态)的可能性很低。人类-非洲类人猿的陆地适应可能不会追溯到中新世中期。较少

This study aims to clarify the evolutionary processes concerning the origin(s) of the terrestriality in the human-African ape clade. For this purpose, the talar joint of the Miocene apes was examined. Movements of the subtalar joint during inversion-eversion were observed in living anthropoids by using the CT scanner, and osteological and kinesiological associations were investigated. The 3-D morphology of the posterior talar articular surface of the calcaneus was measured in Proconsul major, P.nyanzae (ca.19-18 Ma), and Nacholapithecus (ca.15Ma) as well as eight living anthropoids. The proportion of the posterior talar facet and the articular surface axis in the fossil calcanei exhibit the primitive anthropoid pattern. However, movements of the posterior subtalar joint in the fossil apes show a certain degree of rotations and ab-/adduction during in-and eversion of the foot as well as dorsi-and plantarflexion. This type of functional adaptation differs from those in living large platy … More rrhines in which only the dorsi-and plantarflexion are dominated. The posterior talar facet in these fossil apes is unique in that the posterior and anterior part of the facet are peculiarly flat and the intermediate part is well flexed or convexed. Probably, the posterior subtalar joint presumed either the fully plantarflexed or dorsiflexed position when the foot is variously inverted or everted.The posterior part of the articular surface exhibits strong inclination on the medial side. This causes a greater amount of the lateral rotations and/or adduction associated with the plantar flexion. Differing from this condition, cercopithecids has a shortened articular surface, resulting in a smaller range of movements and greater stability of the joint. This condition reflects the semi-terrestrial phase of the primitive cercopithecids. The articular surface of Pan has a less convex and smooth intermediate part. The long axis of the articular surface is strongly angled with the calcanean axis. These specializations enhance the stability of the joint through various positions and a greater component of the rotations in inversion-eversion movement. The fossil calcanei have a wide range of inversion-eversion and high stability in fully inverted of everted position though less than in living apes, thus, are unlikely adapted for ground locomotion. The morphology seen in Pan could have been developed from that of the fossil calcanei. However, the possibility that terrestrially adapted (like morphology of cercopithecids) stage existed in between them is low. Probably, The terrestrial adaptation in human-African ape clade does not go back up to the Middle Miocene. Less