Africa's Gregory Rift Valley is an anthropologist's bread and butter. The Valley's Olduvai Gorge section is where Louis and Mary Leaky found fossilized skulls and bones of Homo habilis, thought by some to be the earliest truly human species. The first skeletal remains of Australopithicus afarensis, better known as Lucy, were found in Ethiopia's Afar Triangle, in the far north end of the Valley. In fact, anthropologists believe the species lived exclusively on the Rift Valley floor.
Well, that's what they believed until recently, when an international team led by Emma Mbua and Masato Nakatsukasa reported they'd found A. afarensis remains in the Kenyan highlands, outside Nairobi and just east of the Rift Valley. That discovery suggests Lucy and her ilk may have been more adaptable than anthropologists thought—and they already thought A. afarensis was pretty adaptable.
Lucy may have been more adaptable than anthropologists thought.
"A. afarensis was previously known from northern Ethiopia to northern Tanzania," the team writes in the Journal of Human Evolution, but evidence of the species in Kenya—which lies between Ethiopia and Tanzania—was scarce, and there was no evidence of it outside the Rift Valley itself. "Although the Gregory Rift Valley has been the focus of paleoanthropologists' attention in East Africa for many years, surveys of the Rift shoulder may open a new perspective for African mammal and hominin evolution during the Pliocene," between about 5.3 and 2.5 million years ago.
Researchers began to focus on the area after locals in Ongata Ronga, a settlement about 10 miles southeast of Nairobi, reported finding fossilized bones along the nearby Kantis River in 1991. Eventually, as fossil reports became more common, Mbua, Nakatsukasa, and their team found teeth and forearms from an adult male and two infants, which they later identified as Australopithicus afarensis.
That discovery not only expands the physical range of the species, but also the range of habitat in which it was able to survive. Back when Lucy roamed the Gregory Rift Valley, the area had a fair number of trees and was relatively dry. In contrast, an analysis of carbon isotopes left in the enamel of both the Australopithicus afarensis and other fossilized mammal teeth suggests the Kantis site was grassier, more open, and more humid than the Rift Valley sites.
"The presence of A. afarensis in both sites, therefore, suggests a greater tolerance of this hominin species for varying habitats," Mbua, Nkatsukasa, and their collaborators write. "Perhaps this environment variability foreshadows the greater adaptability of early Homo," which likely arrived on the scene around 2.8 million years ago.
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