National geographic 2019
The hominin's face was not quite as massive or as rugged as Lucy's, but it was still robust, the researchers reported today (Aug. 28) in the journal Nature. The canine teeth were smaller than those of earlier hominids but larger than those of A. afarensis like Lucy. The lower jaw protruded, ape-like. That's far different from the relatively flat faces of modern humans and other species of the genus Homo, which first evolved around 2.8 million years ago.
Like other australopiths, the face of A. anamensis was long and sloping, unlike the flat faces of modern humans. The dimensions of its teeth and jaws also make sense: Later australopiths had large, wide faces to accommodate the bones and muscles needed to power through tough diets. While A. anamensis had a more robust face than earlier primates, it wasn’t as large as those of its later cousins.
Questions about how afarensis evolution.
One key feature in early hominin skulls is how much the skull narrows behind the eye sockets. Older, more primitive hominins tend to have more constricted skulls than younger ones. The new skull of A. anamensis narrows considerably behind the eye sockets. That feature could clarify the identity the “Belohdeli frontal,” a 3.9-million-year-old fragment of australopith skull found in 1981.
When the Belohdeli frontal was first discovered, some researchers thought it belonged to A. afarensis, but they couldn’t be sure. The situation got murkier once A. anamensis was discovered. Researchers couldn’t confirm whether the bone belonged to A. anamensis, since there were no clear-cut frontals from that species.
Because the Belohdeli frontal is older than the new skull, the find suggests that A. anamensis and A. afarensis overlapped in time from 3.8 to 3.9 million years ago. That’s an evolutionary shakeup: Scientists had thought that successive generations of A. anamensis evolved into A. afarensis, a straight-line process that would have precluded any overlap. Instead, the researchers argue that by 3.9 million years ago, one group of A. anamensis had branched off from the rest and evolved into A. afarensis while other groups of A. anamensis stuck around.