Recently recovered Kenyapithecus mandible and its implications for great ape and human origins.

We report here a Kenyapithecus africanus juvenile mandible recovered from middle Miocene (ca. 14-16 million years) deposits of Maboko Island (Lake Victoria), Kenya. Symphyseal and dental attributes of the mandible distinguish K. africanus, a species widely regarded as the earliest known member of the great ape and human clade, from other Miocene large-bodied hominoids. The Maboko Island mandible exhibits a markedly proclined symphyseal axis, massive inferior transverse torus, mesiodistally narrow, high-crowned, and strongly procumbent lateral incisor, and molars with cingula restricted to the median buccal cleft. Although the presence of some of these conditions in Kenyapithecus was suggested earlier, the fragmentary and ill-preserved nature of previously known specimens led certain authorities to doubt their validity. Our assessment of mandibular and dental morphology indicates that K. africanus diverged after Proconsul and Griphopithecus but prior to the last common ancestor of Sivapithecus, extant great apes, and humans. The robustly constructed mandibular symphysis and anterior dentition suggest that incisal biting played as important a role as thick molar enamel in the dietary adaptations of K. africanus. IMAGES:

本文报道了一件采自肯尼亚维多利亚湖（Lake Victoria）马博科岛（Maboko Island）中中新世（约1400万至1600万年前）地层的非洲肯尼亚古猿（Kenyapithecus africanus）幼年下颌骨。该下颌骨的下颌联合部（symphyseal）与牙齿特征，将非洲肯尼亚古猿——这一被广泛认定为已知最早的类人猿与人类演化支成员的物种——与其他中新世大型类人猿总科（hominoids）区分开来。该下颌骨具有显著前倾的联合轴、发达的下颌下横隆凸、近远中径狭窄、齿冠高耸且强烈前倾的外侧门齿，以及齿带仅局限于颊侧正中沟的臼齿。尽管此前已有研究提出非洲肯尼亚古猿具备部分此类特征，但此前已知标本的碎片化与保存不佳状况，使得部分权威研究者对这些特征的有效性提出质疑。我们对下颌骨与牙齿形态的评估表明，非洲肯尼亚古猿的演化分支晚于原康修尔猿（Proconsul）与格里菲猿（Griphopithecus），但早于西瓦古猿（Sivapithecus）、现生类人猿与人类的最近共同祖先。其强健的下颌联合部与前部齿列特征表明，门齿啃咬行为与厚臼齿釉质一样，在非洲肯尼亚古猿的食性适应中发挥了同等重要的作用。IMAGES: