Becoming human? Jawbone fragment from Ardipithecus ramidus, an apelike creature that may have walked upright.

Walk Like a Man

Ann is a contributing correspondent for Science

The apelike Ardipithecus ramidus just got a stronger toehold on a branch of the human family tree thanks to a new fossil discovery that adds more evidence that the 4.4 million year-old creature walked upright.

Ever since paleoanthropologists found the first fossils of Ardipithecus ramidus in Ethiopia in 1992, researchers have wondered if this apelike creature walked upright--a traditional hallmark of the extended human family. Scientists initially identified A. ramidus as one of the earliest known hominids on the basis of features in its teeth. But a key question has been whether it walked upright like humans and their ancestors--or if it walked on all fours like apes.

In this week's issue of Nature, an international team of researchers led by archaeologist Sileshi Semaw of the CRAFT Stone Age Institute at the University of Indiana reports the discovery of nine new fossils of A. ramidus from Gona, Ethiopia. The team shows that a bit of toe bone recovered at the site curves in a manner that is diagnostic of upright walking.

The fossils from Gona are significant because they show that A. ramidus also lived about 100 kilometers from the Aramis fossil beds where the first fossils of the species were found. "Gona is the only additional picture we have of A. ramidus," says Semaw. As researchers study the animal and plant fossils associated with A. ramidus at Gona, they hope to find out whether this early hominid lived in woodlands like those at Aramis or was able to inhabit more diverse terrain.

Gona first gained fame as a site where the earliest known tools--dating back 2.5 million years--were found. Now, the team's work shows that the site had been a magnet for early members of the human family for millions of years before that, continuing almost to modern times.

This shows that Gona was "a hominid-bearing site whose potential is only beginning to be realized by fieldwork," says paleoanthropologist Tim White of the University of California, Berkeley.

Related Sites
Info on CRAFT Stone Age Institute
Info on Ardipithecus ramidus

Posted in Paleontology