Final answer:
American paleoanthropologist Donald Johanson discovered Australopithecus afarensis, with the most famous specimen being Lucy, in Ethiopia in 1973. Australian anatomist and anthropologist Raymond Dart discovered Australopithecus africanus in South Africa in 1924. These discoveries were crucial to understanding human evolution.
Step-by-step explanation:
The person who discovered Australopithecus afarensis was an American paleoanthropologist named Donald Johanson. He located the species in 1973 when he found approximately 40% of a skeleton in the Afar region of Ethiopia. The most well-known specimen of this species is nicknamed "Lucy" and was dated to around 3.75-2.8 million years ago. Conversely, Australopithecus africanus was first discovered by the Australian anatomist and anthropologist Raymond Dart in 1924. Dart discovered the species when he received a box of fossils from lime quarry workers in South Africa that contained the Taung child's skull.
Australopithecus africanus lived between two and three million years ago, had a slender build, and was bipedal with robust arm bones. Australopithecus afarensis is known for smaller canines and molars in comparison to apes and a brain size of 380 to 450 cubic centimeters. Both species are significant in understanding the evolution of early hominins and their traits, such as bipedalism and brain size, which have informed our knowledge of human ancestry.