Paleontology and Primate Evolution in the Late Oligocene of Kenya

在包含东半球猴子、猿类和人类(卡他类)的灵长类动物的化石记录中，最大的差距之一是在非洲，时间跨度大约在3000万到2000万年前。这一空白现在已被肯尼亚西北部的两个晚渐新世(约2400万至2700万年)遗址所填补，这两个遗址都在2007年6月的初步野外调查中发现了新的灵长类化石。目前的研究旨在从新的研究区域发现更多代表更完整骨骼遗骸的灵长类化石，将灵长类置于地质时代和古环境的坚实框架中，并对它们进行系统发育和古生物学分析。将在Nakwai和Losodk遗址建立野外营地，并将与人类学家、古生物学家、地质学家(包括学生)组成跨学科团队进行研究，以找回灵长类化石、其他哺乳动物、爬行动物和鸟类、对古环境具有重要意义的植物化石以及用于辐射、古地磁和地球同位素研究的岩石样本。总而言之，对这些数据的分析将记录肯尼亚渐新世晚期灵长类进化和古环境的模式。这项工作将整合到已有的关于渐新世早期重要的底层卡他类和早中新世猿类的大辐射的知识中，以更好地理解从原始的早期卡他类到人总科中最早的大型类人猿的进化转变。将讨论几个具有理论重要性的问题。一些问题围绕着对晚渐新世卡他龙的分类评估：真正的人科动物(只包含类人猿和人类的类人族成员)在这个时候存在，还是类人猿的化石灵长类动物是真正的类人猿的前身，或者是真正的人科动物的侧向亲属？正如最新的分子时钟所预测的那样，东半球猴子和猿类之间的进化分裂到这个时候已经发生了吗？其他重要的理论问题围绕着这些早期类猿灵长类动物的适应，以及它们获得类猿特征的顺序，例如它们特有的攀爬运动的骨骼适应，对食果性饮食的牙齿适应，以及与大脑大小增加相关的颅骨适应。渐新世晚期是非洲开始与北部大陆对接的时期，非洲以前是一个岛国大陆，对于这一地理事件是否与非洲气候变化、环境或生态变化或动物群落变化有关，理论上有相当大的兴趣。肯尼亚学生和博物馆工作人员将参与这一项目，许多关键分析和实验室程序将与肯尼亚同事一起进行，为肯尼亚古生物学家提供新的机会和培训。

One of the great gaps in the fossil record of the primate group containing Old World monkeys, apes and humans (catarrhines) has been the one spanning the interval from about 30 to 20 million years ago in Africa. This gap has now been filled by two sites of Late Oligocene age (approximately 24-27 million years old) in northwestern Kenya, both of which yielded new primate fossils during preliminary fieldwork in June, 2007. The current research is designed to find more primate fossils representing more complete skeletal remains from the new research areas, to put the primates into a solid framework of geological age and paleoenvironment, and to conduct phylogenetic and paleobiological analyses of them. Field camps will be established at the sites of Nakwai and Losodok, and research will be conducted with an interdisciplinary crew of anthropologists, paleontologists, geologists, including students, to recover primate fossils, other mammals, reptiles and birds, fossils of paleoenvironentally important plants, and rock samples for radiometric, paleomagnetic, and geo-isotopic studies. Together, analyses of these data will document patterns of primate evolution and paleoenvironment during the Late Oligocene of Kenya. This work will be integrated into existing knowledge of the important basal catarrhines of the early Oligocene and the great radiation of apes in the early Miocene, in order to better understand the evolutionary transition from primitive, early catarrhines to the earliest large-bodied apes of the superfamily Hominoidea. Several issues of theoretical importance will be addressed. Some issues center around taxonomic assessments of Late Oligocene catarrhines: were true hominoids (members of the group containing only apes and humans) present at this time, or are the fossil ape-like primates precursors, or lateral relatives, of true hominoids? Had the evolutionary split between Old World monkeys and apes occurred by this time, as predicted by the latest molecular clocks? Other issues of theoretical importance center around the adaptations of these early ape-like primates, and the sequence in which they acquired ape-like traits, such as skeletal adaptations for their characteristic climbing movements, dental adaptations for frugivorous diets, and cranial adaptations associated with increasing brain size. The Late Oligocene is the period in which Africa, previously an island continent, was beginning to dock with the northern continents, and there is considerable theoretical interest in whether this geographic event was associated with African climatic change, shifts in environment or ecology, or changes in animal communities. Kenyan students and museum staff will be participate in this project, and many of the key analyses and laboratory procedures will be conducted with Kenyan colleagues, providing new opportunities and training for Kenyan paleontologists.