"Ardi" Fossil is described, changing theories on human evolution

No modern ape is a realistic proxy for characterizing early hominid evolution.”

— Science Magazine

An ancient human-like creature that may be a direct ancestor to our species has been described by researchers.

The assessment of the 4.4-million-year-old animal called Ardipithecus ramidus is reported in the journal Science.

Even if it is not on the direct line to us, it offers new insights into how we evolved from the common ancestor we share with chimps, the team says.

Fossils of A. ramidus were first found in Ethiopia in 1992, but it has taken 17 years to assess their significance.

The most important specimen is a partial skeleton of a female nicknamed "Ardi".

A treasure trove of 4.4-million-year-old fossils from the Ethiopian desert is dramatically overturning widely held ideas about the early evolution of humans and how they came to walk upright, even as it paints a remarkably detailed picture of early life in Africa, researchers reported today.

The centerpiece of the diverse collection of primate, animal and plant fossils is the near-complete skeleton of a human ancestor that demonstrates our earliest forebears looked nothing like a chimpanzee or other large primate, as is now commonly believed. Instead, the findings suggest that the last common ancestor of humans and primates, which existed nearly 2 million years earlier, was a primitive creature that shared few traits with modern-day members of either group.

Researchers in the U.S. and Ethiopia on Thursday made public fossils from a 4.4-million-year-old human forebear they say reveals that the earliest human ancestors were more modern than scholars assumed and deepens the evolutionary gulf separating humankind from today's apes and chimpanzees.

The highlight of the extensive fossil trove is a female skeleton a million years older than the iconic bones of Lucy, the primitive female figure that has long symbolized humankind's beginnings.

An international research team led by paleoanthropologist Tim White at the University of California, Berkeley, unveiled remains from 36 males, females and young of an ancient prehuman species called Ardipithecus ramidus, unearthed in the Awash region of Ethiopia since 1994. The creatures take their scientific name from the word for root in the local Afar language. They are not the oldest known homind fossils but they comprise the most complete set discovered so far.

"It is not a chimp and it is not human," said Dr. White. "It gives us a new perspective on our origins. We opened a time capsule from a time and place that we knew nothing about."

Lucy, meet Ardi.

Ardi, short for Ardipithecus ramidus, is the newest fossil skeleton out of Africa to take its place in the gallery of human origins. At an age of 4.4 million years, it lived well before and was much more primitive than the famous 3.2-million-year-old Lucy, of the species Australopithecus afarensis.

Since finding fragments of the older hominid in 1992, an international team of scientists has been searching for more specimens and on Thursday presented a fairly complete skeleton and their first full analysis. By replacing Lucy as the earliest known skeleton from the human branch of the primate family tree, the scientists said, Ardi opened a window to “the early evolutionary steps that our ancestors took after we diverged from our common ancestor with chimpanzees.”

The older hominid was already so different from chimps that it suggested “no modern ape is a realistic proxy for characterizing early hominid evolution,” they wrote.