Frost Stephen R, Gilbert Christopher C, Pugh Kelsey D, Guthrie Emily H, Delson Eric
Department of Anthropology, 1218 University of Oregon, Eugene, Oregon, 97403-1218, United States of America.
Department of Anthropology, Hunter College of the City University of New York, New York, New York, 10065, United States of America; New York Consortium in Evolutionary Primatology, New York, New York, 10024, United States of America; PhD Program in Anthropology, The Graduate Center, City University of New York, New York, New York, 10016, United States of America.
PLoS One. 2015 May 20;10(5):e0125030. doi: 10.1371/journal.pone.0125030. eCollection 2015.
Thumb reduction is among the most important features distinguishing the African and Asian colobines from each other and from other Old World monkeys. In this study we demonstrate that the partial skeleton KNM-ER 4420 from Koobi Fora, Kenya, dated to 1.9 Ma and assigned to the Plio-Pleistocene colobine species Cercopithecoides williamsi, shows marked reduction of its first metacarpal relative to the medial metacarpals. Thus, KNM-ER 4420 is the first documented occurrence of cercopithecid pollical reduction in the fossil record. In the size of its first metacarpal relative to the medial metacarpals, C. williamsi is similar to extant African colobines, but different from cercopithecines, extant Asian colobines and the Late Miocene colobines Microcolobus and Mesopithecus. This feature clearly links the genus Cercopithecoides with the extant African colobine clade and makes it the first definitive African colobine in the fossil record. The postcranial adaptations to terrestriality in Cercopithecoides are most likely secondary, while ancestral colobinans (and colobines) were arboreal. Finally, the absence of any evidence for pollical reduction in Mesopithecus implies either independent thumb reduction in African and Asian colobines or multiple colobine dispersal events out of Africa. Based on the available evidence, we consider the first scenario more likely.
拇指缩小是区分非洲和亚洲疣猴彼此以及与其他旧世界猴的最重要特征之一。在本研究中，我们证明了来自肯尼亚科比福拉的部分骨骼标本KNM - ER 4420，其年代可追溯至190万年前，被归类为上新世 - 更新世疣猴物种威廉氏长尾猴（Cercopithecoides williamsi），相对于中间掌骨，其第一掌骨明显缩小。因此，KNM - ER 4420是化石记录中首次有记录的猕猴科拇指缩小的实例。在第一掌骨相对于中间掌骨的大小方面，威廉氏长尾猴与现存的非洲疣猴相似，但与猕猴、现存的亚洲疣猴以及晚中新世疣猴小疣猴（Microcolobus）和中猴（Mesopithecus）不同。这一特征清楚地将长尾猴属（Cercopithecoides）与现存的非洲疣猴分支联系起来，使其成为化石记录中首个明确的非洲疣猴。长尾猴对陆地生活的颅后适应性很可能是次生的，而其祖先疣猴类（以及疣猴）是树栖的。最后，中猴没有任何拇指缩小的证据，这意味着要么非洲和亚洲疣猴的拇指缩小是独立发生的，要么是多次从非洲向外扩散的疣猴事件。基于现有证据，我们认为第一种情况更有可能。
