toe bone (which belonged to a bipedal organism). Again, evidence from other fossils suggests that Ardipithecus lived in a forested environment. This is quite different from the open savannah conditions in which hominids were thought to have become bipedal. That all these species existed so close to the origin of hominids suggests that even then our family tree could be described as bushy, rather than having the single linear progression from species to species that is so often presented in images of human evolution. This large group of species comprises both the gracile and the robust australopithecines. Recently some scientists have suggested that some species presently assigned to the Homo clade would be better placed in Australopithecus - an example of how rapidly our understanding of our evolutionary past is changing, and of the reviews, discussion and disagreements that characterise scientific research. Australopithecus anamensis The earliest known australopithecine is Australopithecus anamensis , which lived between 4.2 and 3.9 million years ago. This has teeth and jaws that strongly resemble those of older fossil apes. However, they were very likely bipedal (based on the structure of the tibia ) and had human-like upper limbs. Maeve Leakey's research team suggests that anamensis may be ancestral to all later hominids. Australpithecus afarensis The best-known member of this species is " Lucy " , discovered in 1974 by Don Johanson & Tom Gray and estimated to be around 3.2 million years old ( afarensis lived from 3.9 to 3 million years ago). This is