River-margin habitat of Ardipithecus ramidus at Aramis, Ethiopia 4.4 million years ago.

The nature and type of landscape that hominins (early humans) frequented has been of considerable interest. The recent works on Ardipithecus ramidus, a 4.4 million years old hominin found at Middle Awash, Ethiopia, provided critical information about the early part of human evolution. However, habitat characterization of this basal hominin has been highly contested. Here we present new sedimentological and stable isotopic (carbon and oxygen) data from Aramis, where the in situ, partial skeleton of Ar. ramidus (nicknamed 'Ardi') was excavated. These data are interpreted to indicate the presence of major rivers and associated mixed vegetations (grasses and trees) in adjacent floodplains. Our finding suggests that, in contrast to a woodland habitat far from a river, Ar. ramidus lived in a river-margin forest in an otherwise savanna (wooded grassland) landscape at Aramis, Ethiopia. Correct interpretation of habitat of Ar. ramidus is crucial for proper assessment of causes and mechanisms of early hominin evolution, including the development of bipedalism.