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Fossil discovery could unravel mystery of how humans learned to walk (+video)

The discovery of foot bone fossils from an early hominin may help unlock the mystery of how humans learned to walk upright.  

By Charles ChoiLiveScience Contributor / March 28, 2012

This image provided by the Cleveland Museum of Natural History shows a bone fragment from a 3.4-million-year-old partial foot recovered during an excavation in Ethiopia. A new study determined that the foot belonged to a human relative that lived around the same time as Lucy, the famous early hominid.

AP Photo/Celeveland Museum of Natural History, Yohannes Haile-Selassie

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Ancient foot bones from a recently discovered pre-human species, which had opposable big toes like a gorilla's, could shed light on how the ancestors of humanity came to walk upright, researchers say.

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A few million years ago, our ancestors stopped climbing trees and started walking upright, on two feet. To work out how and when this happened, researchers look for fossils -- and recently they found a surprising set of foot bones in Ethiopia. The foot is about 3.4 million years old, making it roughly the same age as 'Lucy' and her species, Australopithecus afarensis. But while Lucy's species had feet much like modern humans, the new foot has an opposable big toe, like a chimp. So do the foot bones represent a new species of hominin? Watch the video and decide.

Humans dominate the planet partly because walking upright frees their hands for tool use. Among the earliest known relatives of humanity to walk upright was Australopithecus afarensis, the species including the famed "Lucy." This hominin is a leading candidate for direct ancestor of the human lineage, living about 2.9 million to 3.8 million years ago in East Africa.

Although Lucy and her kin were bipedal, there is debate about how much they depended on life in trees. Now scientists also have fossils of a hitherto unknown species of hominin that lived about the same time and place as Australopithecus afarensis. Judging by its feet, this newfound relative of humanity was a tree-dweller – which suggests that, in turn, Australopithecus afarensis adapted to life walking on the ground.

"In biology, if you have two closely related species that live close to each other, they may start to diverge in what niches they occupy," said researcher Bruce Latimer, a paleoanthropologist at Case Western Reserve University.

Since this newfound hominin possessed feet good for climbing trees, "it does really hammer home the idea that Australopithecus afarensis might have been a bipedal animal that committed itself to the ground and walking long distances," Latimer told LiveScience. [Photos of New Hominin Species]

The 3.4-million-year-old fossils were discovered in 2009 in a part of Ethiopia known as Burtele. Nowadays this area is hot and dry, with temperatures skyrocketing up to 110 degrees Fahrenheit (43 degrees Celsius). But "nearby fossils of fish, crocodiles and turtles and physical and chemical characteristics of sediments show the environment was a mosaic of river and delta channels adjacent to an open woodland of trees and bushes," said fellow Case Western researcher Beverly Saylor.

Scientists have long argued that Australopithecus afarensis was the only pre-human species between 3 million and 4 million years ago. These new fossils of an unknown hominin species are the first incontrovertible evidence that at least two pre-human species lived at the same time and place around 3.4 million years ago.

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