Study of hominoid evolution and human origin in East Africa

该项目旨在通过对肯尼亚北部纳乔拉和桑布鲁-丘陵地区中新世中晚期的发掘，阐明人类和非洲猿类谱系分化的过程。1995年至1998年野外调查和发掘的主要主题如下：在纳乔拉的BG-K化石遗址(KNM-BG 35251)发现了保存完好的中新世中新世类人猿雌性肯雅猿的下颌骨和上颌骨。这是第一个保存了几乎完整的牙列的Kenyapithecus标本。此外，在同一地点还发现了一具雄性Kenyapithecus(KNM-BG 35250)的相关骨骼。该标本保存了近一半的颅后元素，是迄今已知的最完整的中新世人类标本之一。除了古人类化石外，还收集了许多非灵长类动植物化石。通过这些发现，出现了以下几点。1)Nachola Kenyapithecus不同于肯尼亚东部其他地区的同类动物，是一个新物种；2)它的迁徙方式基本上是树栖的，尽管它偶尔会利用地面；3)它的栖息地包含一个重要的森林成分，尽管东非的森林在中中新世有减少的趋势。通过K-Ar分析，确定了肯雅猿猴的年龄为15 Ma。在Samburu Hills，主要进行地表化石采集和地质调查，在Nakapoleterado地区，包括22号遗址，1982年采集了晚中新世大型古人类Samburupithecus的上颌骨，Moru(=Mt.)阿本尤地区。通过K-Ar分析，确定Samburupithecus的年龄为9.5 Ma。似乎在森阿本尤附近有化石沉积，这一地区有望进行古生物和古环境调查。

This project aims to clarify the process of the divergence of humans and African apes lineages through excavation of the middle to late Miocene in Nachola and Samburu-Hills area, northem Kenya.The main topics of the survey and excavation in the 1995-1998 field seasons are as follows : a well-preserved mandible and maxilla of female Kenyapithecus, a middle Miocene hominoid, was discovered from the BG-K fossil site in Nachola (KNM-BG 35251). This is the first Kenyapithecus specimen which preserves an almost complete tooth row. Furthermore, an associated skeleton of a male Kenyapithecus (KNM-BG 35250) was discovered from the same site. This specimen preserves nearly half of the postcranium elements and is one of the most complete Miocene hominoid specimens ever known. Besides hominoid fossils, many non-primate animal and plant fossils were collected. By these discoveries, the followings are appeared. 1) Nachola Kenyapithecus is distinct from congeners from other localities in eastern Kenya and to be a new species, 2) its locomotor mode is basically arboreal even though it might utilize the ground level occasionally, and 3) its habitat includes a significant forest element despite of le trend of decrease of the forests in east Africa through the middle Miocene. By the K-Ar analysis, the age of Kenyapithecus was precisely determined as l5 Ma. In the Samburu Hi1ls, the surface collection of fossils and geological survey were conducted mainly.in the Nakapoleterado region which includes the Site 22, where the maxilla of Samburupithecus, a late Miocene large hominoid, were collected in 1982, and the Moru (=Mt.) Abenyou region. By a K-Ar analysis, the age of Samburupithecus was determined as 9,5 Ma. It is appeared that there are fossiliferous sediments near Moru Abenyou and that this area to be expected for paleontological and paleoenvironmental surveys.