Final answer:
The transition from Australopithecus to Homo shows trends of reduced facial protrusion, smaller jaws and teeth, and increased brain size. Robust australopithecines had features for strong jaw muscles, while Homo species developed traits like a sagittal keel and canine fossa.
Step-by-step explanation:
The evolutionary transition from the genus Australopithecus to the genus Homo is characterized by several important trends in skull morphology. Early hominins like Australopithecus afarensis had skulls that were smaller than modern humans, with prominent jaws, larger teeth, and a sloped forehead. As evolution progressed towards the genus Homo, there was a trend towards reduced prognathism - a less protruding face - and smaller jaws and teeth.
Gracile australopithecines such as A. afarensis and A. africanus displayed more pronounced facial projection (prognathism) and flatter cheeks without a sagittal crest, while the robust australopithecines had features like the sagittal crest to accommodate stronger jaw muscles for chewing tough plant materials. In contrast, Homo species such as H. habilis and Homo erectus show a larger brain capacity (over 600 cc), a more globular skull, and reduced jaw and tooth sizes compared to their australopithecine predecessors.
Other notable skull features in later Homo species include a sagittal keel, seen in H. erectus, as well as a canine fossa, a facial depression above the canine tooth, also found in Homo antecessor and modern humans. These traits are thought to have developed to accommodate a diet that was gradually including more meat alongside foraged plant foods, requiring less robust chewing apparatus.