Australopithecus afarensis (3.6 to 2.9 million years ago)
Australopithecus afarensis had a very low forehead, a face that projected far forward, and a very prominent brow ridge. A. afarensis is the earliest species for which we have reliable brain and body size estimates, thanks to a rich fossil record for the species.
The brain of A. afarensis was about one-third the size of the average modern human brain, or about the same size as a modern ape's brain. Males and females varied significantly in body size, with males standing approximately 4 feet 11 inches tall and weighing 100 pounds and females standing about 3 feet 5 inches tall and weighing about 62 pounds. Males also typically had large crests on top of their skulls; females did not.
The knee and pelvic bone structure of A. afarensis were very humanlike, leaving no doubt that A. afarensis walked upright. A. afarensis probably inhabited the savannas and open woodlands where they likely found fruits, seeds, and roots.