San Diego Museum of Man - Footsteps Through Time

Timestone 4
4.4 million years ago
Ardipithecus ramidus

This is one of the earliest hominid fossils ever found and the first dated as older than 4 million years. This species lived in what is now Ethiopia in Africa and had both ape-like and human-like features.

Scientists believe that Ardipithecus ramidus was very similar to the common ancestor of chimps and hominids (two groups that split between 7 and 5 million years ago). Although fossils of this species show chimp-like features-body size, shape of skull base and lower jaw, small lower molars, large canine teeth, and thin tooth enamel-it was not a chimp. The foramen magnum and shape of the pelvis imply bipedalism (walking upright on two legs), which is a hominid feature.

Sculptural replica of fossil jaw fragment with tooth of a child
Ardipithecus ramidus
Found in Aramis, Ethiopia, in Africa, in 1992 by Alamayehu Asfaw, a member of Tim White's team
Age: 4.4 million years

Several fossil finds of Ardipithecus in Ethiopia since 1997, by Tim White, Giday WoldeGabriel, Yohannes Haile-Selassie, and colleagues, date to 5.8 to 5.2 million years ago.

Bipedalism
Walking upright: A major first step

The skeleton holds the clues
To determine if a primate species walked upright, scientists look for key skeletal features-a basin-shaped pelvis, S-shaped spine, hip and knee joints supporting inward-slanting thigh bones, and a big toe aligned with the other toes. They also look at the foramen magnum (the hole where the spine enters the skull). If it is at the base of the skull, the species probably walked upright.