Ardi (Ardipithecus ramidus)

Ardi is the nickname of a partial skeleton of Ardipithecus ramidus, an early human relative that lived in what is now Ethiopia about 4.4 million years ago. Fossils were recovered from the Middle Awash region of the Afar, at a site called Aramis, from 1994 onward by a team led by Tim White, Berhane Asfaw and Giday WoldeGabriel, and the skeleton was described in a set of papers in Science in 2009. The skeleton was a female about 120 centimeters tall and roughly 50 kilograms, with a brain about the size of a chimpanzee's, around 300 to 350 cubic centimeters.

Ardi lived long before Lucy and sits closer to the time when the human line split from the chimpanzee line, probably about 6 to 7 million years ago. Its pelvis was shaped so that it could walk upright on two legs on the ground, but it also kept an opposable big toe, like an ape's thumb, that let it grip branches. Its canine teeth were small and not sharply pointed, unlike a chimpanzee's, which some researchers read as a sign of less male-to-male fighting.

The setting surprised many. Fossil pollen and animals around the skeleton suggest a woodland with trees, not an open grassland, so upright walking did not begin because early hominins left the forest, as older textbooks suggested. The skeleton also challenged the idea that our ancestor looked like a chimpanzee, since Ardi's hands and feet differ from those of living African apes, suggesting that chimpanzees and gorillas have also changed a great deal. Not every scientist agrees on how well Ardi walked or whether it is a direct ancestor, and the interpretation is still debated.