Final answer:
Hominoids are classified under the genus Homo based on criteria including a larger brain size, tool use, reduced facial protrusion, and adaptations for bipedal locomotion. Additionally, the morphology of hands, feet, and dental features are considered. Homo habilis demonstrates many of these characteristics, exhibiting a mix of modern and ancient traits.
Step-by-step explanation:
Characteristics of Hominoids
The genus Homo includes species that exhibit a variety of characteristics indicating a closer relation to modern humans than to other apes. Criteria for classifying a species under the genus Homo, as proposed by paleoanthropologists like Mary Leakey, Louis Leakey, and John Napier include: a brain size over 600 cc, a round, globular skull, tool use, reduced prognathism with smaller jaws, humanlike postcranial features, and feet adapted for walking upright. Homo habilis is one of the earliest species in the genus Homo and had a brain size around 661-700 cc, with hands capable of dexterity for making tools due to structural changes and a repositioning of the thumb.
Additional traits to consider when classifying hominoids outside of bipedalism include small jaws and teeth, ape-like long arms, presence of a sagittal keel, and humanlike feet with arches. Early Homo species such as Homo erectus were nearly as efficient at bipedal locomotion as modern humans, with adaptations such as a broader pelvis, longer legs, and arched feet, though they still possessed larger jaws and teeth and a relatively small brain. Morphological traits and behaviors are key in distinguishing hominoids from other primates and identifying lineage relationships within the Homo genus.