Planet Earth

A Fossil Named Ardi Shakes Up Humanity's Family Tree

80beatsBy Eliza StricklandOct 1, 2009 4:57 PM
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Humanity has a new matriarch: a hominid named Ardi who lived in Ethiopia 4.4 million years ago. Anthropologists have unveiled the results of 17 years of research on a new species named Ardipithecus ramidus, presenting a rich trove of fossils including the partial skeleton of the small-brained, 110-pound female. Ardi is 1.2 million years older than the famed "Lucy," of the species Australopithecus afarensis, and experts say the find fundamentally changes our understanding of human evolution. Study coauthor Tim White says that

Ardi provides clues to what the last common ancestor shared by humans and chimps might have looked like before their lineages diverged about 7 million years ago.... But despite being "so close to the split," says White, the surprising thing is that she bears little resemblance to chimpanzees, our closest living primate relatives [Time].

Ardi's pelvis, leg, and feet bones indicated that she walked upright on two feet, but her opposable big toes suggest that she was also comfortable climbing trees. Her hand, arm, and shoulder bones indicate that she didn't often swing through the trees, though; instead she probably walked on her palms along tree branches like some extinct apes.

Based on Ardi's anatomy, it appears that chimpanzees may actually have evolved more than humans — in the scientific sense of having changed more over the past 7 million years or so [Time].

In a special issue of the journal Science that will be published later today, researchers present 11 papers covering many aspects of Ardipithecus ramidus, and drawing information from the bone fragments of 35 individuals. The researchers also examined the

remains of animals, seeds and pollen uncovered at the excavation site [that] reveal it to have been a woodland where colobus monkeys swung in trees full of swifts, doves and lovebirds, and spiral-horned antelope, elephants, shrews and early forms of peacock roamed the forest floor below [The Guardian].

That woodland habitat contrasts with the savanna where Lucy was thought to dwell, and it has big implications for our understanding of what caused hominids to rise to their feet. If the researchers are correct in thinking that

Ardi walked upright as well as climbed trees, the environmental evidence would seem to strike the death knell for the "savanna hypothesis"—a long-standing notion that our ancestors first stood up in response to their move onto an open grassland environment [National Geographic News].

So how did bipedalism take off? One provocative idea rests on Ardi's dental records. Researchers say her species

lacks many typical features of chimpanzees, including large male canine teeth — a sign, say the researchers, that the ultra-aggressive social behaviors seen in chimpanzees were lost early in the human lineage. If so, male A. ramidus may have competed for female attention by bringing them food, rather than fighting each other. That could have contributed to the evolution of pair-bonding behavior [Wired.com].

Some anthropologists believe that early hominids may have switched from a four-limbed gait to a two-legged stride so that the males could more easily bring home the bacon. Related Content: The Loom: Ardipithecus: We Meet At Last has much more on the findings 80beats: Did a Strangely Human-Like Primate Give Rise to Monkeys, Apes, and Us? 80beats: No Tarzans Here: Earliest Humans Quickly Lost Their Ape-Like Climbing Abilities DISCOVER: The 2% Difference examines what sets us apart from chimpanzees Image: J.H. Matternes

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