Editor's note: At the request of illustrator J.H. Matternes and
Science/AAAS, we are removing the illustrations of
Ardipithecus ramidus that were once featured here. The illustrations may be viewed in a scientific paper.
This row of images shows the male canine condition of Ardipithecus ramidus
(center digital image) intermediate in size between humans (left) and chimpanzees. The reduced size of canine teeth is an indication of a shift in social behavior away from male-male aggression, and is one of the hallmarks of the human lineage.
Finding the trait in Ardipithecus
suggests that a social structure involving more cooperation between males evolved very early after the divergence between the chimpanzee and human lineages. A. ramidus'
molars and premolars were small compared to those of later australopithecines and had thinner enamel, reflecting differences in diet.
In addition to the partial skeleton found in 1994, bone fragments of at least 35 other Ardipithecus ramidus
individuals were excavated at the Aramis site in the Middle Awash region of the Afar Depression in Ethiopia.
While its massive forearms and long, curved fingers show A. ramidus
was a climber, the upper portion of its pelvis had evolved away from an apelike condition to accommodate strong muscles that assisted in walking upright. This more human-like pelvis shape can be seen in later human ancestors, such as Australopithecus afarensis.
Image courtesy Science/AAAS