WASHINGTON (AFP) -– A group of U.S. scientists have disputed claims that “Ardi,” man's oldest known ancestor, lived in forested areas -- an assertion key to understanding of how and why humans evolved.

Science magazine dubbed 'Ardipithecus ramidus' its “Breakthrough of the Year” in 2009, and the hypothesis that the human forebear lived in dense woodlands was used to argue against the so-called “savanna hypothesis” of human evolution.
But in a critique published Thursday, a team of eight geologists and anthropologists from seven universities argue there is little evidence to suggest Ardi actually lived in woodlands.
“There is abundant evidence for open savanna habitats,” said University of Utah geochemist Thure Cerling, lead author of the critique published in the May 28 issue of Science.
The savanna hypothesis argues that the ancestors of today's humans descended from trees and began to walk upright because of an expansion of savannas -- grassy plains with trees and shrubs.
Ardi, the fossilized skeleton of a female human forebear, is believed to be 4.4 million years old and was discovered in what is now Ethiopia.
The researchers who uncovered the fossil published some eleven papers in Science detailing the hominid's features, including an opposable big toe and supple hands to grasp tree branches.
The team that discovered Ardi also found fossilized wood, seeds, plants and animals including monkeys, parrots and snails, which they said indicated the area had been a woodland with a cooler and wetter climate than today.
But that analysis is disputed by Cerling and his colleagues, who examined the same data as the team that found Ardi, including ancient soils and tiny fossilized grains of silica from plants.