An older guy has sauntered into Lucy’s life, and some researchers believe he stands ready to recast much of what scientists know about the celebrated early hominid and her species.
Excavations in Ethiopia’s Afar region have uncovered a 3.6-million-year-old partial male skeleton of the species Australopithecus afarensis. This is the first time since the excavation of Lucy in 1974 that paleoanthropologists have turned up more than isolated pieces of an adult from the species, which lived in East Africa from about 4 million to 3 million years ago.
A nearly complete skeleton of an A. afarensis child has been retrieved from another Ethiopian site (SN: 9/23/06, p. 195).
Discoverers of the skeleton, led by anthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History, consider this a Desi Arnaz moment. As the late actor often exclaimed on his classic television show, “Lucy, you got some ’splainin’ to do!” But other researchers are not so convinced that the new fossil changes much of what they already knew about Lucy and her kind.
Haile-Selassie’s team has dubbed its new find Kadanuumuu, which means “big man” in the Afar language. At an estimated 5 to 5½ feet tall, he would have towered over 3½-foot-tall Lucy. Excavations between 2005 and 2008 in a part of Afar called Woranso-Mille — about 48 kilometers north of where Lucy’s 3.2-million-year-old remains were found — yielded fossils from 32 bones of the same individual.
Big Man’s long legs, relatively narrow chest and inwardly curving back denote a nearly humanlike gait and ground-based lifestyle, according to a preliminary report published online June 21 in the Proceedings of the National Academy of Sciences. Lucy has often been portrayed as having had a fairly primitive two-legged gait and a penchant for tree climbing.
Big Man’s humanlike shoulder blade differs as much from those of chimpanzees as it does from those of gorillas, Haile-Selassie says. The shape of that bone, combined with characteristics of five recovered ribs, suggest to Haile-Selassie’s team that Big Man’s chest had a humanlike shape. Earlier reconstructions of Lucy’s rib cage had endowed her with a chimplike, funnel-shaped chest.
So despite chimps’ close genetic relationship to people, he says, this new fossil evidence supports the view that chimps have evolved a great deal since diverging from a common human-chimp ancestor roughly 7 million years ago and are not good models for ancient hominids.
Big Man’s shoulder blade bolsters recent analyses of 4.4-million-year-old Ardipithecus ramidus that also challenge traditional views of ancient hominids as chimplike (SN: 1/16/10, p. 22).
Estimates of Lucy’s build were based on comparisons to chimps and indicated to some scientists that she lacked the easy, straight-legged stride of people today. Haile-Selassie and his colleagues suspect that their final reconstruction of Big Man’s anatomy will provide a better model for assessing what Lucy looked like.
“Whatever we’ve been saying about afarensis based on Lucy was mostly wrong,” Haile-Selassie says. “The skeletal framework to enable efficient two-legged walking was established by the time her species had evolved.”
Lucy’s legs were short because of her small size, he adds. If Lucy had been as large as Big Man, her legs would have nearly equaled his in length, Haile-Selassie estimates.
Although lacking a skull and teeth, Big Man preserves most of the same skeletal parts as Lucy, as well as a nearly complete shoulder blade and a substantial part of the rib cage.
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“This beautiful afarensis specimen confirms the unique skeletal shape of this species at a larger size than Lucy, in what appears to be a male,” remarks anthropologist Carol Ward of the University of Missouri in Columbia.
A long-standing debate over how well Lucy’s kind walked and whether they spent much time in the trees appears unlikely to abate as a result of Big Man’s discovery, though. “There’s nothing special I can see on this new find that will change anyone’s opinion” on how the species navigated the landscape, comments Harvard University anthropologist Daniel Lieberman.
Haile-Selassie’s team disagrees. Big Man demonstrates that A. afarensis spent most of the time on the ground, the researchers conclude.
“They were good walkers, but we don’t know how well they ran,” Haile-Selassie says. Big Man’s long-legged stride indicates that members of his species could have made 3.6-million-year-old footprints found more than 30 years ago at Laetoli, Tanzania (SN Online: 3/22/10),
Anthropologist Owen Lovejoy of Kent State University in Ohio, a coauthor of the new paper, regards Big Man as having been an “excellent runner.” His pelvis supported humanlike hamstring muscles and, as indicated by the Laetoli footprints, his feet had arches, Lovejoy holds.
Fossil hominid skeletons as complete as Big Man “are few and far between,” says anthropologist William Jungers of Stony Brook University in New York. But the new find mostly confirms what was already known about Lucy, he asserts. Lucy’s kind, including Big Man, were decent tree climbers, even if they couldn’t hang from branches or swing from limb to limb as chimpanzees do, he says.
“Riddle me this,” asks Jungers in considering Hailie-Selassie’s emphasis on a ground-dwelling A. afarensis. “Where did they sleep? Did they wait for fruit to fall to the ground? Where did they go to escape predators?”
Groups of A. afarensis individuals must have devised ground-based strategies to ward off predators, Lovejoy responds. Some big cats would have negotiated trees better than Lucy’s kind, he notes.
Jungers also doubts Lovejoy and Haile-Selassie’s contention that a nearly humanlike gait had evolved in A. afarensis. Big Man includes only one nearly complete limb bone, from the lower left leg, which makes it difficult to estimate how long his legs were relative to his arms, Jungers contends.
Limb remains of hominid species that came after afarensis indicate that they evolved increasingly longer legs and a more efficient walking stance, Jungers adds.
In his view, hips conducive to walking slowly with legs wide apart evolved in an even earlier hominid, 6-million-year-old Orrorin tugenensis (SN: 3/29/08, p. 205)
] and characterized later Australopithecus species, including Lucy’s kind.
Haile-Selassie counters that features of Big Man’s pelvis related to walking closely resemble those of a 1.4-million to 900,000-year-old female Homo erectus from another Ethiopian site (SN: 12/6/08, p. 14).
Big Man’s legs also demonstrate that the comparably long legs of nearly 2-million-year-old South African hominids don’t represent a transition to the Homo genus (SN: 5/8/10, p. 14), Haile-Selassie asserts.
Haile-Selassie doubts that additional pieces of Big Man’s skeleton will turn up. “If anything more was there, we would have found it by now,” he says with a resigned laugh.
Back story images courtesy of Smithsonian Institution