Ardipithecus ramidus was first reported in 1994; in 2009, scientists announced a partial skeleton, nicknamed ‘Ardi’.
The foot bones in this skeleton indicate a divergent large toe combined with a rigid foot – it’s still unclear what this means concerning bipedal behavior. The pelvis, reconstructed from a crushed specimen, is said to show adaptations that combine tree-climbing and bipedal activity. The discoverers argue that the ‘Ardi’ skeleton reflects a human-African ape common ancestor that was not chimpanzee-like. A good sample of canine teeth of this species indicates very little difference in size between males and females in this species.
Ardi’s fossils were found alongside faunal remains indicating she lived in a wooded environment. This contradicts the open savanna theory for the origin of bipedalism, which states that humans learned to walk upright as climates became drier and environments became more open and grassy.
Over 100 specimens of Ardipithecus ramidus have been recovered in Ethiopia. Even though it has some ape-like features (as do many other early human species), it also has key human features including smaller diamond-shaped canines and some evidence of upright walking. It may have descended from an earlier species of Ardipithecus that has been found in the same area of Ethiopia, Ardipithecus kadabba.
Ardipithecus ramidus individuals were most likely omnivores, which means they enjoyed more generalized diet of both plants, meat, and fruit. Ar. ramidus did not seem to eat hard, abrasive foods like nuts and tubers.
How do we know they were omnivores?
The enamel on Ar. ramidus teeth remains show it was neither very thick nor very thin. If the enamel was thick, it would mean Ar. ramidus ate tough, abrasive foods. If the enamel was thin, this would suggest Ar. ramidus ate softer foods such as fruit. Instead, A. ramidus has an enamel thickness between a chimpanzee’s and later Australopithecus or Homo species, suggesting a mixed diet. However, the wear pattern and incisor sizes indicate Ar. ramidus was not a specialized frugivore ( fruit-eater). Ar. ramidus probably also avoided tough foods, as they did not have the heavy chewing specializations of later Australopithecus species.