Final answer:
The africanus and robustus skulls were originally thought to be those of ancient humans, but further research disproved this idea. The cranial capacity of these species was significantly smaller than that of Homo sapiens. Australopithecus afarensis overlapped with early Homo.
Step-by-step explanation:
The skulls of Australopithecus africanus and Australopithecus robustus were originally thought to be those of ancient humans. However, further research and analysis disproved this idea. The key difference between these species and the genus Homo is their cranial capacity. The average cranial capacity of Homo sapiens is about 1,400 cubic centimeters, while the cranial capacity of Australopithecus africanus was approximately 500 cubic centimeters, which is less than one-third the size of a modern human brain.
Species that overlapped with early Homo include Australopithecus afarensis, which lived between two and three million years ago. It had a smaller skull compared to modern humans, with a sloped forehead and larger teeth, and a prominent jaw.