Fossil may boost case for earliest human ancestor

Twenty years ago, scientists discovered a 7-million-year-old skull that they concluded belonged to a creature who walked upright and was our earliest known ancestor. Not everyone was convinced. Now, the researchers are back with more evidence they say strengthens their case.

Their new study published on Aug. 24 analyzed arm and leg fossils found near the skull in Africa, looking for signs of walking on two feet instead of on all fours. When early humans started walking upright, it marked a key moment in our split away from apes.

In the paper in the journal Nature, researchers again place the creature just on the human side of that evolutionary divide.

The fossil species, named Sahelanthropus tchadensis, walked upright while still being able to climb around in trees, they reported.

The species has been dated to around 7 million years ago, which makes it the oldest known human ancestor, by a long shot.

That's about a million years older than other early known hominins.

But it's been a source of fierce debate since the fossils were first unearthed in Chad in 2001.

Researchers, also led by scientists at the University of Poitiers in France, initially looked at the fossil creature's skull, teeth and jaw. They argued that the creature must have walked on two feet and held its head upright, based on the location of the hole in the skull where the spinal cord connects to the brain.

Other experts weren't swayed by the early evidence.

The latest work includes a thighbone that was not linked to S. tchadensis at first and went unstudied for years. Other researchers at the French university found the bone in the lab's collection and realized it probably belonged to the fossil species.

Compared to bones from...

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