Southern apes

Just one year ago to the day saw the announcement of a new hominin species, Australopithecus deyiremida, discovered in Ethiopia, based on a jaw and some teeth. There’s good news coverage from Carl Zimmer. The new species overlaps in time with Australopithecus afarensis (the long lasting species to which Lucy belonged) and Australopithecus bahrelghazali, as well as Kenyanthropus platyops. This might be more evidence that human evolution for a long time was extremely “bushy,” involving a proliferation of species with variable combinations of traits. But it could also be telling us that what constitutes a species is less clear cut than you might have been taught in high school biology – an issue we’ll keep coming back to.

People want to know who their relatives are, so an awful lot of press coverage is about whether A. deyiremida is a human ancestor or not. It’s already been claimed that Kenyanthropus platyops looks closer to genus Homo than other hominins from around the time period. But right now we’re at a point where new discoveries seem to make it harder, not easier, to draw lines connecting ancestors and descendants.

Maybe it’s best to step back and notice some general traits of australopithecines (“southern apes”). We’ve talked a lot about bipedalism. Australopithecines are clearly bipedal, but there’s an ongoing debate over whether some or all of them might also have spent some time climbing in trees. Certainly this sounds like a good idea for getting away from predators but just how important it was is in dispute. Australopithecus teeth are telling us something too. Mostly the front teeth are reduced compared to chimpanzees and gorillas, but the back teeth are large and thick enameled, implying that australopithecines, more than African great apes, were supplementing their fruit diet with tough hard-to-chew “fallback” foods. There’s a lot of variation between species though: A. deyiremida apparently looks closer to later species than A afarensis.

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