H. naledi made worldwide headlines last year when researchers announced the discovery of an unusually large collection of odd-looking Homo fossils in the bowels of a South African cave system. Presentations at the annual meeting of the American Association of Physical Anthropologists on April 16 underscored key uncertainties about the hominid.
One of the biggest mysteries: H. naledi’s age. Efforts are under way to date the fossils and sediment from which they were excavated with a variety of techniques, said paleoanthropologist John Hawks of the University of Wisconsin–Madison. An initial age estimate may come later this year if different dating techniques converge on a consistent figure. A solid date for the fossils is essential for deciphering their place in Homo evolution and how the bones came to rest in a nearly inaccessible cave.
CAVE SPECIES A member of the team that climbed into Dinaledi Chamber to retrieve fossils is shown at work after reaching H. naledi’s hiding space.
P.H.G.M. DIRKS ET AL/ELIFE 2015 (CC BY 4.0)
Some presenters reasserted that H. naledi intentionally dropped dead comrades into an underground chamber, where their bones were later found by cave explorers and then scientists. But others raised questions. Even paleoanthropologist and team leader Lee Berger of the University of the Witwatersrand in Johannesburg hedged his bets.
“It’s way too early to tell how H. naledi bodies got in the chamber,” Berger said.
Berger’s group recovered 1,550 H. naledi fossils from a minimum of 15 individuals of all age groups (SN: 10/3/15, p. 6). Slender researchers wended through narrow passageways in South Africa’s Rising Star cave system and squeezed down a vertical chute to reach pitch-dark Dinaledi Chamber. There, they found hominid fossils scattered on the floor and in a shallow, 20-centimeter-deep excavation.
Berger’s team assigned the bones to H. naledi based on an unexpected mix of humanlike features and traits typical of Australopithecus species from more than 3 million years ago.
Fossil analyses presented at the meeting challenged a suggestion by some researchers, both before and during the meeting, that H. naledi actually represents a variant of Homo erectus, a species known to have existed by 1.8 million years ago (SN: 11/16/13, p. 6).
H. naledi possessed a shoulder unlike those of other Homo species, said team member Elen Feuerriegel of the Australian National University in Canberra. The Rising Star hominid’s collarbone and upper arm bone resemble corresponding Australopithecus bones, she reported. H. naledi’s shoulder blades must have been positioned low and behind the chest, an arrangement more conducive to climbing trees than running long distances.
H. naledi’s hand was built both for climbing and gripping stone implements, said Tracy Kivell of the University of Kent in England. Her analysis of 150 hand bones, including a nearly complete hand, showed a humanlike wrist and thumb combined with Australopithecus-like curved fingers..