Meet the Relatives

Carl Zimmer has a fairly informative blog posting on the latest hominid relative added to our line:

Some 4.4 million years ago, a hominid now known as Ardipithecus ramidus lived in what were then forests in Ethiopia. Fifteen years ago, Tim White of Berkeley and a team of Ethiopian and American scientists published the first account of Ardipithecus, which they had just discovered. But it was just a preliminary report, and White promised more details later, once he and his colleagues had carefully prepared and analyzed all the fossils they had unearthed. “Later,” it turned out, meant 15 years.

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But then, with the discovery of Ardipithecus and a few other hominid fossils, the record of our ancestry got pushed back millions of years. The oldest fossil that’s been identified as a hominid, Sahelanthropus tschadensis, dates back between 6 and 7 million years old. But scientists have only found pieces of the Sahelanthropus skull. Another species, Orrorin tugenensis, is 6 million years old; it’s represented by little more than a leg bone.

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At first, Ardipithecus ramidus was yet another scrappy pre-Lucy fossil. The first report offered details about part of a 4.4 million-year-old jaw bone–a remarkable jaw bone, but just a jaw bone nonetheless. Soon after, White’s team found more fossil bones, from the hominid’s hand, skull, pelvis, feet, and on and on–110 pieces all told.

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White and his colleagues found so many teeth of different Ardipithecus individuals that they could compare male and female canines with some confidence. The male teeth turn out to be surprisingly blunted. This result suggests that hominids shifted away from a typical ape social structure early in our ancestry. If this was a result of males forming long-term bonds with females and helping raise young, this shift was able to occur while hominids were still living a very ape-like life. Ardipithecus existed about 2 million years before the oldest evidence of stone tools, suggesting that technology was not the trigger for the evolution of nice hominid guys.

Update 2009oct10: Here a Discovery channel bit over the reconstruction of Ardipithecus: