Seed Magazine has a nice summary of the most important discovery in human paleontology for quite some time. The 4.5 million-year-old Ardipithecus stands at the very initial stage of human evolution, where humans began bipedal walking in earnest. From the article:
What makes Ardipithecus singular is the skeleton: To anatomists, Ardi is not a mere point on a map. It is the map. As paleoanthropologist C. Owen Lovejoy describes it, Ardi gives us a view of a previously unknown “adaptive plateau” among early hominins—a suite of anatomical and behavioral characteristics that lasted for a long, stable period in the early Pliocene environment. The Ardipithecus form might account for the bulk of the whole story of human evolution—a kind of hominin that was different from anything that came before or after. [...] So how close is Ardipithecus to the last common ancestor? In the current issue of Genetics, yet another study of the human and chimpanzee genomes places the divergence between them at only 4.3 million years—a shade younger than Ardipithecus.Ardipithecus is like humans in that "she had small, human-like canine teeth. Her molars were smaller, but stout—not at all like those of chimpanzees or gorillas." Also her skull "was carried above her spine most of the time, an indication that she saw the world from a vertical, upright posture." The reason that this find is so important to Anthropology is because "the real 'missing link' —the common ancestor of humans and chimpanzees—may have been a lot like Ardi."
[image] Seed Magazine
John Hawks "Uncovering Ardi: What We Know" Seed Magazine October 5, 2009 (Accessed November 1, 2009)
[*] The article mentions where the real research was presented--in Science magazine. I have happened to have that edition, but there is an excellent online version available of all those materials found at their site: Online Extras: Ardipithecus ramidus. There is also an informative summary video to be found there.