Final answer:
Homo habilis had a larger brain size, smaller teeth, and jaws compared to australopithecines, and exhibited humanlike traits such as the dexterity needed for tool use and bipedal walking. However, they retained some primitive features such as long arms and were significantly shorter in height. These characteristics emphasize the humanlike evolution from the more ape-like australopithecines.
Step-by-step explanation:
Homo habilis, often referred to as "handy man," exhibited various key characteristics that distinguished it from its predecessor species, the australopithecines. With a larger brain size of about 600 to 750 cubic centimeters, H. habilis demonstrated a significant leap towards modern humanlike features when compared with Australopithecus. The brain of H. habilis was larger than that of australopithecines, nearing the lower range of modern humans and offering a greater cognitive capacity.
Moreover, H. habilis had smaller teeth and jaws, and their third molar was larger than the other molars, a trait shared with some early Homo species. The skull of H. habilis was shaped more like H. erectus, with a round, globular form. Their hands also evolved to be capable of dexterity needed for making and using tools, which is underscored by the repositioning of the thumb for a more precise grip. These characteristics imply that tool use was significant in the Homo lineage, marking a definitive step away from the more ape-like features of australopithecines.
Despite these humanlike features, H. habilis still retained some primitive features such as long arms, which may indicate that they were adept climbers and had not fully transitioned from arboreal habitats. While bipedal and walking with a human gait, H. habilis still had some traits suggesting time spent in the trees. H. habilis was also physically smaller than modern humans, with adult heights averaging between three to four feet. Nevertheless, their postcranial features and humanlike feet with arches and ankles were adapted for walking bipedally, a key human trait.