Final answer:
The gracile group of Australopithecus, including species like A. afarensis and A. africanus, is characterized by a pronounced facial projection, smaller teeth and jaws, and no sagittal crest. These species had adaptations for bipedalism, yet retained some arboreal features, and existed approximately from 4 to 2 million years ago.
Step-by-step explanation:
The gracile Australopithecus group, including species like Australopithecus afarensis, Australopithecus anamensis, Australopithecus africanus, and Australopithecus sediba, exhibit several distinctive features. They displayed a more pronounced projection of the face (prognathism), less flared cheeks with no sagittal crest, and generally smaller teeth and jaws compared to their robust counterparts. These gracile species appeared around 4 million years ago (MYA) and disappeared around 2 MYA.
One notable example, Australopithecus afarensis, shows evidence of bipedalism with a pelvic structure similar to that of modern humans, despite retaining some ape-like features such as long, curved fingers and toes suitable for climbing. This species, along with others in the gracile category, offers insight into the evolution of bipedalism and various adaptive strategies of early hominins.