NEW OLIGOCENE VERTEBRATE LOCALITIES FROM NORTHERN KENYA(TURKANA BASIN)

摘要

In contrast to the Neogene fossil assemblages, Late Paleo-gene mammal localities are rare in Africa. The most famous onesare situated in the Fayum depression in Egypt, from which sev-eral rich fossil mammal communities dated from 37 to 29 Ma(e.g., Seiffert, 2006) have been discovered. Other later Paleo-gene localities on the Afro-Arabian plate include the sites ofDor El Talha (Idam Unit: Wight, 1980), Zellah (Fejfar, 1987),and Jebel Hasawnah (Thomas et al., 2004) in Libya; Thaytinitiand Taqah (Thomas et al., 1989) in the Sultanate of Oman;Gebel Bou Gobrine and Bled Mellaha (Arambourg and Burol-let, 1962) in Tunisia; Mbeya (Stevens et al., 2005, 2006) in Tan-zania; and Malembe (Pickford, 1986) in Angola. Additionally, afew late Oligocene fossiliferous localities are known only in east-ern Africa: Chilga (Kappelman et al., 2003; Sanders et al., 2004;Jacobs et al., 2005) in Ethiopia; Wedeg Melatse Farm (Shoshaniet al., 2006) in Eritrea; and Lothidok (Leakey et al., 1995) innorthern Kenya. However, these late Oligocene sites to datehave yielded a limited ordinal diversity of vertebrate taxa. Con-sequently, this part of mammal evolutionary history in Africais still poorly known. Yet, this period is critical because it fillsa chronological and evolutionary gap just prior to the Oligo-Miocene faunal turnover, documenting the transition betweenarchaic African and modern Neogene faunas, which resultedfrom significant exchanges with Eurasian faunas. An increasedknowledge of the fossil record for this period is necessary to un-derstand the impact of paleogeography and paleoenvironmentalchanges on this major transition in the African faunal composi-tion. The Lokichar Basin, one of the oldest sedimentary basinson the western side of Lake Turkana, northern Kenya, repre-sents an interesting area to document this context, because itdeveloped during the Paleogene (Morley et al., 1992; Tiercelinet al., 2004).