The creationists are going to love this. 
Rather than indicating a direct link to modern humans, the familiar features of some purported human ancestors, including Ardipithecus ramidus, might be explained by convergent evolution
Some of the most solid evidence for Ardi being included in the hominin branch is her small canine teeth. But the researchers are quick to point out that other ancient non-hominin species, including Oreopithecus and Ouranopithecus, also came to have reduced canine teeth, "presumably as a result of parallel shifts in dietary behavior in response to changing ecological conditions," the researchers suggest in their article. "Thus, these changes are in fact, not unique to hominins."
The placement of a hole at the base of the skull, known as the foramen magnum, also might suggest Ardi as an upright walker, and thus perhaps a solid hominin. But in looking to other apes, "this feature is more broadly associated with differences in head carriage and facial length, rather than uniquely with bipedalism," Wood and Harrison note. Some extinct primates, such as Oreopithecus bambolii, evolved outside of the human line but nevertheless possessed similarly hominin-like traits, which, the authors write, "encourage researchers to generate erroneous assumptions about evolutionary relationships."
Some of the most solid evidence for Ardi being included in the hominin branch is her small canine teeth. But the researchers are quick to point out that other ancient non-hominin species, including Oreopithecus and Ouranopithecus, also came to have reduced canine teeth, "presumably as a result of parallel shifts in dietary behavior in response to changing ecological conditions," the researchers suggest in their article. "Thus, these changes are in fact, not unique to hominins."
The placement of a hole at the base of the skull, known as the foramen magnum, also might suggest Ardi as an upright walker, and thus perhaps a solid hominin. But in looking to other apes, "this feature is more broadly associated with differences in head carriage and facial length, rather than uniquely with bipedalism," Wood and Harrison note. Some extinct primates, such as Oreopithecus bambolii, evolved outside of the human line but nevertheless possessed similarly hominin-like traits, which, the authors write, "encourage researchers to generate erroneous assumptions about evolutionary relationships."
So, does Ardi represent a true step toward humanity, or should she remain up in the side branches of the evolutionary tree? White and his fellow authors do not propose to have a definitive answer, but through painstaking analysis of the fossil data and surroundings, they conclude in the overview paper that, "There are no apparent features sufficiently unique to warrant the exclusion of Ar. ramidus as being ancestral to Australopithecus,".
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The problem is we don't really know what very early apes (i.e. primapes which lived before the human-ape split) looked like. Some have traits which we once thought were exclusive to human ancestors. For example - Anoiapithecus brevirostris had an unusually flat and human-like face, but it lived 12 million years ago. Another, Oreopithecus bambolii, mentioned above, has such mixed features people cannot decide whether it was merely an extinct ape or an early hominid.
Any thoughts? Was Ardi a human ancestor after all? What traits should we be looking for to determine which apes gave rise to humans?
