Discovering "Ardi"



A diagrammatic representation of Ardipithecus ramidus/Drawing by Jay Matternes

It’s been 17 years since an international team of paleonathropologists first found the fossilized bones and teeth of a new hominid in the Middle Awash River Valley of Ethiopia. University of Tokyo paleoanthropologist Gen Suwa actually discovered the first tooth of what was the species he and his colleagues named Ardipithecus ramidus, published in the journal Nature in 1994. The paper revealed the first information on the 4.4 million year old hominid, which lived just a few million years after the divergence between the evolutionary line leading to chimpanzees and the line leading to modern Homo sapiens. Project co-director and University of California Berkeley paleontologist Tim White and colleagues promised the world more information would come soon.

And then for the past decade and a half, 47 scientists from 10 nations have studied this Ethiopian horizon to piece together the story of A. ramidus. The team has gathered bones of at many additional  individuals from the same species, piecing together the puzzle of what this species represented. The team’s discovery of a female Ardipithecus skeleton - nicknamed Ardi - serves as the centerpoint of a special issue of the journal Science published October 2nd, celebrating the 150th anniversary since the publication of Charles Darwin’s On the Origin of Species. The special issue includes eleven scientific articles on A. ramidus as well as other fossil plants and animals that lived at the same time. As the oldest hominid skeleton, Ardi is significant indeed.

Ardi and her brethren lived 4.4 million years ago. Before this, the oldest known hominid was the famous “Lucy” - the small-brained but fully bipedal Australopithecus who lived 3.2 million years ago. Before the discovery of A. ramidus, scientists thought our common ancestor with chimps – still undiscovered - came down from the trees and ventured it open grasslands, which then spurred the evolution of bipedalism (walking on two hindlimbs). But Ardi’s bones and joints reveal the species moved through the trees on four limbs but walked upright on the ground.

Ardi has a relatively small brain for a hominid. The brain is about the same size as a modern chimp or bonobo, smaller than Australopithecus, including the famous “Lucy,” and a mere fifth the size of the modern human brain. Ardi’s teeth show the species did not specialize in any particular diet but ate whatever they could find- food such as small mammals, birds, snails, eggs, nuts, plants, and fruit.  Digs throughout the study area have revealed the world Ardi lived in. Sparse woodlands dominated, with freshwater springs here and there, with patches of dense forest. Tree and plants species associated with A. ramidus include fig and hackberry, and animals include owls, parrots, mice, bats, porcupines, monkeys, antelopes, pigs, rhinos, elephants, and giraffes.

Contrast this process of slow-cooked science (as Carl Zimmer called it) with the way paleontologists publicized and promoted the so-called “missing link” Darwinius masillae a few months back. In that case, it wasn’t long before another team of scientists recently published an opposing analysis of its significance (I blogged about this last week). While that fossil discovery certainly deserved merit, it was way over-hyped by the scientists and the television channel that would air a show on the subject. In the case of Ardi, a documentary began filming ten years back when the unearthing was still underway. Discovering Ardi aired a few weeks ago on the Discovery Channel, and the online supplementary material is fantastic, including several video clips of the scientists, artist's renditions, and more.

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