Wednesday, February 23, 2005

Tech scientist helps date fossils of early walkers

John Fleck The Albuquerque Journal

Special to El Defensor Chieftain

Newly discovered fossils from Ethiopia have filled in a gap in our genealogy with 4.5-million-year-old hominids who were among the first of our ancestors to walk upright.

"One of the curiosities with humanity is the question of where we came from," said Sileshi Semaw of Indiana University, leader of the team that made the find.

"Just by nature we're pretty interested in our heredity," said Bill McIntosh of the New Mexico Institute of Mining and Technology, who helped determine how old the fossils were.

The scientists found 30 bones that appear to be from nine separate individuals of a creature called "Ardipithecus ramidus," which lived in what is now Ethiopia, one of the cradles of human evolution.

The research, published Jan. 20 in the British scientific journal Nature, suggests Ardipithecus ramidus lived in an environment that was part woodland and part grassland. The era, 4.5 million years ago, is a critical time in understanding human evolution.

Studies comparing our DNA with that of our nearest relatives, chimpanzees, suggest the two species share a common ancestor 6 million to 8 million years ago.

Coming soon after that, Ardipithecus ramidus represents one of the early steps in the evolutionary path that distinguishes us from modern chimpanzees.

According to Semaw, the shape of the creature's toe bones suggests it walked upright.

To pin down when Ardipithecus ramidus lived, a sample of basalt the size of a golf ball, found in a layer adjacent to where the bones were found, was brought to McIntosh's Socorro lab, where he analyzed potassium and argon in the rock to determine its age.

Another sample was sent to a lab at the University of California, Berkeley, for dating.

According to Semaw, fossils older than 4.3 million years are rare. The famed fossil "Lucy," found in Ethiopia by Donald Johanson three decades ago, is younger at roughly 3 million years old. According to Semaw, fossil bones from some 400 hominids of Lucy's age have been found, but only a handful in the older age range of the newly discovered Ardipithecus ramidus.

Semaw said the team has found other fossils from the area that are more than 5 million years old and are under study.

One open question is the environment in which Ardipithecus ramidus lived. Understanding the environment in which our ancestors developed into modern humans is a crucial piece in the evolutionary story.

One key question is the extent of grasslands. Other fossils from the Ardipithecus family have been found in woodland settings, according to Semaw, but there is evidence for grasslands in the area where the new fossils were found.

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