Michelle Drapeau,

département d'Anthropologie, Université de Montréal

This research proposes to document an important milestone in hominin evolution, the Ardipithecus-Australopithecus transition, by furthering our knowledge of the environment in which this transition occurred and to improve our understanding of the morphological changes involved in this important speciation event. More specifically, this programme proposes to conduct field investigations in the Mursi Formation of the Lower Omo Valley, southern Ethiopia. At more than 4 million years, the Mursi Formation is the oldest geological sequence of the Omo Group. It corresponds to the period when the Australopithecus genus arose, the first taxon with well-documented, habitual bipedal locomotion and still believed to be the most likely ancestor to the genus Homo. The Formation also corresponds to the period when Ardipithecus, a genus recently described that retained an important arboreal component in its locomotion and lacking typical Australopithecus dietary adaptations, is no longer found in the sediments. Despite the close temporal occurrences of these taxa and their relatively large morphological differences, Ardipithecus is considered the most likely ancestor of Australopithecus. It is important to characterize the nature of the Ardipithecus-Australopithecus morphological transition that occurred during that period, but it is also imperative that the environmental context of the origin of the Australopithecus be well known in order to understand some of the mechanisms that led to that evolutionary radiation. Despite the importance of that time period in hominin evolution, very few localities of that age are identified. Investigation of the Mursi Formation will help test specific hypotheses concerning the important Ardipithecus-Australopithecus transition. Long-term goals will include integration of the Mursi Formation into the regional picture of environmental change and evolution in East Africa.