Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Am J Phys Anthropol. 2010 Nov;143(3):365-82. doi: 10.1002/ajpa.21327.
Old World monkeys represent one of the most successful adaptive radiations of modern primates, but a sparse fossil record has limited our knowledge about the early evolution of this clade. We report the discovery of two partial skeletons of an early colobine monkey (Microcolobus) from the Nakali Formation (9.8-9.9 Ma) in Kenya that share postcranial synapomorphies with extant colobines in relation to arboreality such as mediolaterally wide distal humeral joint, globular humeral capitulum, distinctly angled zona conoidea, reduced medial trochlear keel, long medial epicondyle with weak retroflexion, narrow and tall olecranon, posteriorly dislocated fovea on the radial head, low projection of the femoral greater trochanter, wide talar head with a greater rotation, and proximodistally short cuboid and ectocuneiform. Microcolobus in Nakali clearly differs from the stem cercopithecoid Victoriapithecus regarding these features, as Victoriapithecus is postcranially similar to extant small-sized terrestrial cercopithecines. However, degeneration of the thumb, a hallmark of modern colobines, is not observed, suggesting that this was a late event in colobine evolution. This discovery contradicts the prevailing hypothesis that the forest invasion by cercopithecids first occurred in the Plio-Pleistocene, and shows that this event occurred by the late Miocene at a time when ape diversity declined.
旧世界猴是现代灵长类动物中最成功的适应性辐射之一，但由于化石记录稀少，我们对该类群的早期进化了解有限。我们报告了在肯尼亚 Nakali 组（9.8-9.9 百万年前）发现的两种早期丛猴（Microcolobus）的部分骨骼，它们在后肢骨骼上具有与现生丛猴相关的树栖共衍征，例如肱骨远端关节面宽、肱骨头球状、明显成角的滑车切迹、内侧滑车嵴减小、内侧上髁长且弱后弯、狭窄而高的鹰嘴、桡骨头后脱位的窝、股骨大转子低突、距骨头宽且有更大的旋转、以及跗骨和楔骨短而窄。在这些特征上，Nakali 的 Microcolobus 与茎猴科的 Victoriapithecus 明显不同，因为 Victoriapithecus 的后肢骨骼与现生小型陆生猴科相似。然而，拇指退化，这是现代丛猴的一个特征，没有观察到，这表明这是丛猴进化中的一个晚期事件。这一发现与流行的假说相矛盾，该假说认为，猴科动物首先在更新世-全新世侵入森林，而这一事件发生在中新世晚期，当时猿类的多样性下降。
