Jungers W L, Godfrey L R, Simons E L, Chatrath P S
Department of Anatomical Sciences, School of Medicine, State University of New York, Stony Brook, NY 11794-8081, USA.
Proc Natl Acad Sci U S A. 1997 Oct 28;94(22):11998-2001. doi: 10.1073/pnas.94.22.11998.
Recent paleontological discoveries in Madagascar document the existence of a diverse clade of palaeopropithecids or "sloth lemurs": Mesopropithecus (three species), Babakotia (one species), Palaeopropithecus (three species), and Archaeoindris (one species). This mini-radiation of now extinct ("subfossil") lemurs is most closely related to the living indrids (Indri, Propithecus, and Avahi). Whereas the extant indrids are known for their leaping acrobatics, the palaeopropithecids (except perhaps for the poorly known giant Archaeoindris) exhibit numerous skeletal design features for antipronograde or suspensory positional behaviors (e.g., high intermembral indices and mobile joints). Here we analyze the curvature of the proximal phalanges of the hands and feet. Computed as the included angle (theta), phalangeal curvature develops in response to mechanical use and is known to be correlated in primates with hand and foot function in different habitats; terrestrial species have straighter phalanges than their arboreal counterparts, and highly suspensory forms such as the orangutan possess the most curved phalanges. Sloth lemurs as a group are characterized by very curved proximal phalanges, exceeding those seen in spider monkeys and siamangs, and approaching that of orangutans. Indrids have curvatures roughly half that of sloth lemurs, and the more terrestrial, subfossil Archaeolemur possesses the least curved phalanges of all the indroids. Taken together with many other derived aspects of their postcranial anatomy, phalangeal curvature indicates that the sloth lemurs are one of the most suspensory clades of mammals ever to evolve.
近期在马达加斯加的古生物学发现证明了古原狐猴科（或“懒猴”）这一多样分支的存在：中狐猴属（三种）、巴氏狐猴属（一种）、古原狐猴属（三种）和古大狐猴属（一种）。这种现已灭绝（“亚化石”）狐猴的小型辐射演化与现存的大狐猴科（大狐猴、原狐猴和毛耳狐）关系最为密切。尽管现存的大狐猴科以其跳跃的杂技能力而闻名，但古原狐猴科（可能除了鲜为人知的巨型古大狐猴外）展现出众多适应非前肢前位或悬垂姿势行为的骨骼设计特征（例如，较高的肢间指数和灵活的关节）。在此，我们分析了手和脚近端指骨的曲率。指骨曲率通过计算夹角（θ）得出，它因机械使用而产生，并且在灵长类动物中已知与不同栖息地的手和脚功能相关；陆生物种的指骨比树栖同类更直，而高度悬垂的物种如猩猩则拥有最弯曲的指骨。作为一个群体，懒猴的特征是近端指骨非常弯曲，超过蜘蛛猴和合趾猿，接近猩猩的指骨弯曲程度。大狐猴科的指骨曲率约为懒猴的一半，而更偏向陆地生活的亚化石古狐猴在所有大狐猴类中拥有最不弯曲的指骨。结合它们颅后解剖结构的许多其他衍生特征，指骨曲率表明懒猴是有史以来进化出的最具悬垂性的哺乳动物分支之一。
