The search for the earliest fossil evidence of the human lineage has been concentrated in East Africa. Here we report the discovery of six hominid specimens from Chad, central Africa, 2,500 km from the East African Rift Valley. The fossils include a nearly complete cranium and fragmentary lower jaws. The associated fauna suggest the fossils are between 6 and 7 million years old. The fossils display a unique mosaic of primitive and derived characters, and constitute a new genus and species of hominid. The distance from the Rift Valley, and the great antiquity of the fossils, suggest that the earliest members of the hominid clade were more widely distributed than has been thought, and that the divergence between the human and chimpanzee lineages was earlier than indicated by most molecular studies.

All six known specimens of the early hominid Sahelanthropus tchadensis come from Toros-Menalla site 266 (TM 266), a single locality in the Djurab Desert, northern Chad, central Africa. Here we present a preliminary analysis of the palaeontological and palaeoecological context of these finds. The rich fauna from TM 266 includes a significant aquatic component such as fish, crocodiles and amphibious mammals, alongside animals associated with gallery forest and savannah, such as primates, rodents, elephants, equids and bovids. The fauna suggests a biochronological age between 6 and 7 million years. Taken together with the sedimentological evidence, the fauna suggests that S. tchadensis lived close to a lake, but not far from a sandy desert, perhaps the oldest record of desert conditions in the Neogene of northern central Africa.

Both dust and silica phytoliths have been shown to contribute to reducing tooth volume during chewing. However, the way and the extent to which they individually contribute to tooth wear in natural conditions is unknown. There is still debate as to whether dental microwear represents a dietary or an environmental signal, with far-reaching implications on evolutionary mechanisms that promote dental phenotypes, such as molar hypsodonty in ruminants, molar lengthening in suids or enamel thickening in human ancestors. By combining controlled-food trials simulating natural conditions and dental microwear textural analysis on sheep, we show that the presence of dust on food items does not overwhelm the dietary signal. Our dataset explores variations in dental microwear textures between ewes fed on dust-free and dust-laden grass or browse fodders. Browsing diets with a dust supplement simulating Harmattan windswept environments contain more silica than dust-free grazing diets. Yet browsers given a dust supplement differ from dust-free grazers. Regardless of the presence or the absence of dust, sheep with different diets yield significantly different dental microwear textures. Dust appears a less significant determinant of dental microwear signatures than the intrinsic properties of ingested foods, implying that diet plays a critical role in driving the natural selection of dental innovations.

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A survey of Paleogene ungulates from Western Europe is drawn up from the results of previous work on the ungulate lineages of this period and from new data on two groups particularly representative of the Oligocene ungulate fauna: the ruminants and the Cainotheriidae based on new material collected in localities of the Quercy Phosphorites. The history of ungulates from Western Europe at the Eocene±Oligocene transition is marked by different phases of extinction and origination related to environmental changes. In this perspective, the relative diversity of groups and the modi®cations of their tooth morphology, which re¯ect a diet change, resulting from vegetation modi®cations are analysed from the Early Eocene to the Late Oligocene. In Western Europe, the Late Eocene and the Early Oligocene was a period of transition with an important change in faunal and oral composition. The diversity analysis of ungulates suggests that the Grande Coupure is the result of gradual climatic and geographic events that occurred from the Middle Eocene (Mammalian Paleogene (MP)13/14 reference levels) to the Early Oligocene (MP 21/22 reference levels). During this period, it has been demonstrated that important adaptive changes occurred in the ungulate dental pattern (selenodonty in artiodactyls, semihypsodonty in perissodactyls), and appendicular skeleton (fusion of the cuboid and navicular bones of the tarsus in artiodactyls). These morphological modi®cations coincided with environmental changes that were less extreme than in North America. q

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