Study of hominoid evolution and human origin in East Africa

点击翻译按钮获取中文摘要

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.