Australopithecus sediba is two million years old. The species had an awkward walk, enabling them to walk and climb easily.
The bones reveal they had long arms and primitive shoulders like an ape, but their legs could straighten. They also had dexterous hands and a human-like thumb.
"Just a weird, weird combination," Jeremy DeSilva of Boston University said.
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They believe the fossils provide more distinctions from hominid Lucy, who has the most complete set of bones.
"What these papers suggest is that sediba probably doesn't come from the East African species that Lucy comes from," Lee Berger, who discovered the fossil site of Malapa, said.
Lucy is of the species Australopithecus afaraensis and walked the Earth 3.2 million years ago.
Researchers are perplexed by the way Au. sediba walked, as it is much different from any other human-like creature they've discovered.
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The rib cage and spine are "very ape-like at the top and human-like at the bottom," while the species also has the first-ever kneecap.
The bones of five individuals were discovered at the site, and are all very well-preserved. They believe it is because they died from a sink hole.
"This could very well be a family group," DeSilva said. "I have never seen fossils this well preserved. It's unreal. They are stunning."
They provided researchers with the most well-preserved upper limb, and a complete set of foot, leg and hip pieces from an adult female.
It is the complete set of leg and foot bones is the key into discovering their awkward gait.
The female had a strong heel base like humans, but walked on the outside of her foot, leading to her shin, knee and thigh bones to twist inwards.
Though it sounds painful, it likely wasn't for them.
"They have the anatomy that allows them to do this and to do it well," DeSilva said.
But Zeresenay Alemseged, head of the anthropology department at the California Academy of Sciences, said there is not enough evidence to suggest that this is the closest ancestor of modern man.
He said other fossils show clues of our species much before Au. sediba's time.
"The link to homo is not well established. The torso, the clavicle, the foot have many primitive characteristics," he said.