HUMANITY FROM AFRICAN NAISSANCE TO COMING MILLENNIA 103 Keywords: West Africa, Pliocene Biochronology, Palaeoecology

Five palaeontological and geological field missions carried out in the Djourab Desert (Northern Chad) by the French-Chadian Paleoanthropological Mission (MPFT) have resulted in the discovery of about one hundred continental Mio-Plio-Pleistocene vertebrates sites. Until now three areas have been intensively collected: Koro Toro (KT), Kollé (KL) and Kossom Bougoudi (KB). All the fossils come from poorly consolidated subhorizontal sandstone levels that outcrop sporadically amid dunes and sand. Two hominid localities have already been discovered (Brunet et al., 1995 and 1997). One of them has yielded the first australopithecine known from west of the Rift Valley, Australopithecus bahrelghazali Brunet et al., 1996: a new species characterized by several unique features including a shortened face. In spite of biases associated with preliminary collections and some distinct provincialism, the faunas indicate a biochronological age of between 3 and 3.5 Ma for the two hominid sites, between 4 and 5 Ma for Kollé and older than 5 Ma for Kossom Bougoudi. These faunas are representative of mosaic landscapes including fresh water, wooded savannah and grassland. The diverse faunas indicate a closed environment for KB, a more open environment for KL and still more open for KT. Chadian faunas dated between 3 and 6 Ma are critical to an understanding of the evolution of early hominids and their environments. Already the Chadian australopithecines show us that the hominid story is pan-African at least until 3.5 Ma.