Anth121-2008HominidOrigins

Anth121-2008HominidOrigins - Transitional Forms Orrorin...

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Transitional Forms Orrorin tugenensis Sahelanthropus tchadensis Ardipithecus ramidus
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Orrorin tugenensis
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Sahelanthropus tchadensis • Discovered in 2001 in Chad • Based on faunal studies, it is estimated to be between 6 and 7 million years old • This is a mostly complete cranium with a small brain (between 320 and 380 cc) comparable to that of chimpanzees.
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Cranial Comparisons
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Dental Traits
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Differences in Interpretation • Brunet and co-workers consider Toumai to be a hominid, that is, on our side of the chimp-human split and therefore more closely related to us than to chimps. • Others have suggested that it may come from before the point at which hominids separated from chimps • The discoverers of Orrorin tugenensis , ("Millennium Man") has suggested that it may be an early gorilla.
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Ardipithecus ramidus A 4.5-5.8 million year old ape- like hominid from the Aramis site in Ethiopia Two species: A. kadabba (5.2–5.8 Myr) and A. ramidus (4.5 and 4.3 Myr ) Its teeth are small, have thin enamel, and are intermediate in form between those chimpanzees and later australopithecines such as A. afarensis. This suggests that Ardipithecus had not yet adapted to a tough, abrasive diet that required heavy chewing A milk molar is especially primitive and closely resembles a chimpanzee tooth.
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Ecology of Ardipithecus Animal remains found in association with Ardipithecus suggest that it lived in the forest. If this is true, it is of great interest because the selective pressures our ancestors faced in the savannah are usually seen as instrumental in the evolution of bipedalism and other hominid traits.
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Anth121-2008HominidOrigins - Transitional Forms Orrorin...

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