分子证据表明，人科动物（猿和人）与猕猴科动物（“旧世界”猴子）之间在演化上的分开发生在距今2500万年和3000万年之间，但狭鼻猿（猕猴科和人科）的化石证据只追溯到大约2000万年前。Nancy Stevens及其同事发现了同时属于“旧世界”猴子和猿的动物的最早已知证据，从而在一定程度上填补了这一空白。他们所发现的化石是一种同时属于处在进化树根部的人科动物和处在进化树根部的猕猴科动物的动物，是在坦桑尼亚的东非大裂谷中的一个地层发现的，其年代被精确测定为距今2520万年前。这个年代（属于“渐新世”时期）大大延长了两个类群的动物已知曾经共存的时间范围。（生物谷Bioon.com）
生物谷推荐英文摘要：
Nature doi:10.1038/nature12161
Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes
Nancy J. Stevens, Erik R. Seiffert, Patrick M. O’Connor, Eric M. Roberts, Mark D. Schmitz, Cornelia Krause, Eric Gorscak, Sifa Ngasala, Tobin L. Hieronymus & Joseph Temu
Apes and Old World monkeys are prominent components of modern African and Asian ecosystems, yet the earliest phases of their evolutionary history have remained largely undocumented. The absence of crown catarrhine fossils older than ~20 million years (Myr) has stood in stark contrast to molecular divergence estimates of ~25–30?Myr for the split between Cercopithecoidea (Old World monkeys) and Hominoidea (apes), implying long ghost lineages for both clades. Here we describe the oldest known fossil ‘ape’, represented by a partial mandible preserving dental features that place it with ‘nyanzapithecine’ stem hominoids. Additionally, we report the oldest stem member of the Old World monkey clade, represented by a lower third molar. Both specimens were recovered from a precisely dated 25.2-Myr-old stratum in the Rukwa Rift, a segment of the western branch of the East African Rift in Tanzania. These finds extend the fossil record of apes and Old World monkeys well into the Oligocene epoch of Africa, suggesting a possible link between diversification of crown catarrhines and changes in the African landscape brought about by previously unrecognized tectonic activity in the East African rift system.
