Fossils Push Back Bipedalism to 6 Million Years Ago
Mar. 21 -- THURSDAY, March 20 (HealthDay News) -- Far from being a recent, revolutionary development, the ability to walk upright on two legs began at the dawn of human evolution more than six million years ago, new research confirms.
The first detailed examination of the fossilized thigh bones of a 4-foot tall creature called Orrorin tugenensis supports the notion that this very early member of the hominin family tree was bipedal, anthropologists say.
"Upright walking is one of the very first traits in our lineage to occur. So this finding reinforces that and pushes the date back even farther," said study co-author Brian Richmond, associate professor of anthropology at George Washington University in Washington, D.C.
But the study also suggests that bipedalism changed through succeeding millennia, and that, biomechanically speaking, O. tugenensis probably walked differently than modern humans.
Richmond and a colleague, William Jungers, of Stony Brook University in Stony Brook, N.Y., published their findings in the March 21 issue of Science.
French anthropologists first discovered the six-million-year-old group of fossil thigh bones, hand bones and teeth in Kenya in 2000. O. tugenesis -- about the size of today's chimpanzees -- lived in an era close to the very origins of human evolution.
"It's right in the time period where we think chimpanzees and humans first split from each other -- about 5 to 8 million years ago," Richmond said.
Bipedalism was crucial to human development because it "freed up our hands," Richmond explained. These free forelimbs allowed humans and their ancestors to begin to explore the use of tools, for example. Expanded brain size may also have accompanied (and been encouraged by) bipedalism, anthropologists say.
But was O. tugenensis truly human-like? Because bipedalism is a key trait separating hominins from other primates, a close look at the bones -- the thigh bone, especially -- was necessary.
"We took a simple caliper and measured the size of the hip joint and the strength of the shaft of the bone," Richmond said. "Our analysis showed that the overall shape profile of the bone really closely resembles early human fossils from about three to two million years ago."
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