Final answer:
Late australopithecines had diverse anatomical traits that differed from early Homo species, including jaw and tooth size as well as brain size relative to body mass. The evolution from robust and gracile australopithecines to species like Homo habilis and Homo erectus shows a transition towards smaller teeth and jaws, increased cranial capacity, and more pronounced bipedal locomotion suitable for ground-dwelling life.
Step-by-step explanation:
The anatomical differences between late australopithecines and early Homo species can be categorized by various cranial and dental traits, as well as evidence of bipedalism. Late australopithecines, classified into the robust and gracile forms, show diversity in dental and skull morphology. Gracile species like Australopithecus afarensis had smaller teeth and jaws, more pronounced prognathism (protrusion of the jaw), and lacked a sagittal crest. In contrast, the robust australopithecines featured larger teeth and jaws adapted for chewing tough materials, evidenced by a sagittal crest for large jaw muscles.
The transition to early Homo species, such as Homo habilis and Homo erectus, is marked by a reduction in tooth and jaw size, although the third molar remains larger than the other molars in some early Homo species. Early Homo skulls began to show shapes more akin to H. erectus or H. habilis, like the presence of a sagittal keel. Moreover, there was a progressive increase in brain size relative to body mass. Bipedalism became a defining trait with humanlike feet, characterized by arches and ankles, conducive to a human gait, while the adaptation to a terrestrial lifestyle became more pronounced.
Both lineages show evidence of bipedal locomotion, but it is in the change of locomotive ability and cranial capacity where the transition from australopithecines to early Homo species stands out. This reflects the evolutionary pressures of changing environments and the shift towards more complex behaviours in early hominins.