Haile-Selassie, curator and head of Physical Anthropology at The Cleveland Museum of Natural History, said, "Ardipithecus kadabba may also represent the first species on the human branch of the family tree just after the evolutionary split between lines leading to modern chimpanzees and humans."

Between 1997 and 2000, Haile-Selassie recovered 11 hominid specimens from at least five individuals who lived in a wooded environment in Ethiopia between 5 and 6 million years ago. In a 2001 publication in the journal Nature, the bones and teeth were first placed in a new hominid subspecies named Ardipithecus ramidus kadabba.

In the 2002 field season, the scientific team recovered new fossil teeth of Ardipithecus kadabba at a place known as Asa Koma ("Red Hill") along the western margin of the Middle Awash study area, about 180 miles (290 km) northeast of the Ethiopian capital, Addis Ababa.

The team conducted excavations at Asa Koma for a month and discovered six additional teeth - including an upper canine, premolars from both upper and lower jaws and upper molars - belonging to different individuals.

Haile-Selassie said, "The teeth not only revealed dental evolution in the earliest hominids, but they also helped to differentiate the earlier and later species of the genus Ardipithecus."

Haile-Selassie explained, "The upper canine and the lower third premolar are particularly significant in understanding how the dentition evolved from an ape-like common ancestor into the earliest hominids." Professor White added, "This is just what we needed, an unworn upper canine to compare with both earlier and later fossils from Africa."

Dr. Bruce Latimer, executive director of The Cleveland Museum of Natural History, hails this discovery as "a cornerstone in our attempt to reconstruct the first hominids after the split from the common ancestor with chimpanzees."

Some features seen in the new Ardipithecus kadabba teeth have only been seen in fossil and modern apes. They include the more pointed, triangular shape of the upper canine and wear surfaces on the canine and lower premolar.

Other features are clearly hominid-like such as the presence of a well-defined anterior fovea on the lower third premolar and lower canine variants with high mesial crown shoulders, distal tubercles and apical wear.

In addition, the shape and orientation of the canines and lower premolars in living and fossil apes produce a complex that has a honing function. Honing is a mechanism that sharpens the rear edge of the upper canine across the outer face of the lower premolar as the teeth come together during the chewing process.

Haile-Selassie said, "The primitive shape and wear features of the newly discovered teeth from Asa Koma indicate that the last common ancestor of apes and humans had a functional honing complex like that seen in modern apes."

He also pointed out, "More fossils will be needed to understand whether some Ardipithecus kadabba individuals functionally honed or just retained primitive traits based on the interlocking of the projecting canine teeth inherited from the last common ancestor."

On the phylogenetic relationship of Ardipithecus kadabba with the two other known genera of late Miocene hominids, Orrorin and Sahelanthropus, Haile-Selassie and his colleagues state that the three are similar to such an extent that they might belong to a single genus. However, they also suggest that more fossils from late Miocene deposits are needed to confirm this inference.

The descriptive and comparative analysis of the fossils was conducted by three researchers and will be reported in the March 5 issue of the international scientific journal Science. Haile-Selassie is the lead author. Co-authors are: Dr. Gen Suwa of the University Museum, The University of Tokyo; and Dr. Tim White of the Integrative Biology Department, Museum of Vertebrate Zoology, and Laboratory for Human Evolutionary Studies at the University of California at Berkeley.

Related Links
SpaceDaily
Search SpaceDaily
Subscribe To SpaceDaily Express

Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor $5 Billed Once credit card or paypal		SpaceDaily Monthly Supporter $5 Billed Monthly paypal only