Long-Awaited Research on a 4.4-Million-Year-Old Hominid Sheds New Light on Last Common Ancestor
Fifteen years in the making, a dossier of papers on "Ardi" published in
Science suggest that like humans, chimpanzees have undergone substantial evolutionary change Credits: J.H. MATTERNES
A CLEARER PICTURE Since Lucy's discovery in 1974 few, if any, ancient hominid skeletons have elicited such excitement in the scientific world as Ardi, largely because of her unusual completeness. Although she likely lived just two million to five million years after the last human and chimpanzee common ancestor did, "Ardi does not tell us what the last common ancestor was," Lovejoy said at the press briefing. "What
Ardipithecus does tell us [is that] in the human line, the first phases of evolution were upright walking on the ground, and…careful climbing in the trees. That's something very different from what you see in chimpanzees." J. H. MATTERNES
MORE HUMAN HANDS Ardi's hands, although large—to better climb trees—are a far cry from the stiff, strong hands of today's arboreal chimps. The discovery of so many hand bones mark an important discovery for scientists in the field, as other ancient hominid specimens, including Lucy, lack much of the crucial fossil evidence to assert that these animals did not walk on their knuckles as modern chimps and gorillas do.
FINGERED FOOT The feet of
Ar. ramidus are unlike those of latter Lucy or present-day great apes. A widely detached first toe would have allowed for handy grasping of tree branches and trunks to facilitate climbing, as getting around in its forested environment would have been the primary method of travel. It would have, however, also been capable of some terrestrial walking. SCIENCE/AAAS
PRIMITIVE PELVIS Although Ardi's pelvis was badly damaged, researchers were able to reconstruct it using CT scans. The results show that
Ar. ramidus already had adaptations—far different from today's tree-dwelling chimps—that would have allowed it to walk upright, if not as adeptly as the latter, 3.2-million-year-old Lucy, an Australopithecus afarensis. SCIENCE/AAAS Advertisement
SMALLER CANINES In humans [
left] the canine teeth are only slightly longer than the rest of the teeth, whereas male chimpanzees [ right] have long and fearsome canines that they use in conflicts over females. Male Ar. ramidus [ middle] had relatively shorter canine teeth, revealing, as co-author C. Owen Lovejoy noted at a press briefing, "the reduction in the canine in the male took place long before Australopithecus and long before there was any change in diet." SCIENCE/AAAS
REBUILDING THE BRAIN Ardi's skull was badly crushed, but researchers reconstructed its pieces using computer tomography (CT). Unlike the later
Australopithecus, the "Lucy" species, Ar. ramidus still had a relatively small head and brain. Its position and shape also indicate that even earlier, six-million- to seven-million-year-old species that have been disputed are also hominid cousins. SCIENCE/AAAS
PROFILING A 4.4-MILLION-YEAR-OLD COUSIN
Ardipithecus ramidus—"Ardi"—appears to have many features more primitive than both humans and chimps, reinforcing the idea that our last common ancestor was not like modern chimpanzees after all. The 110 pieces of her skeleton that researchers found allowed them to piece together a better picture of how early hominids evolved and started to walk upright. "This was like discovering a time capsule," one of the senior authors, Tim White, said in a press briefing Thursday. J. H. MATTERNES Advertisement Expertise. Insights. Illumination.
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