Final answer:
Fossil evidence, such as changes in skeletal structure and brain size, allows anthropologists to make educated inferences about the adaptations of Homo and robust hominids to life in open environments, including the shift to bipedalism and tool use.
Step-by-step explanation:
Based solely on fossils, anthropologists can discern how Homo and robust hominids adapted differently to life in open environments by examining their physical characteristics. The adaptations to bipedalism seen in hominin fossils offer some of the earliest indications of these adaptations. Features such as the structure of the pelvis, spinal curvature, limb proportions, and foot anatomy suggest changes in locomotion and posture that are consistent with a transition from arboreal to terrestrial living.
The enlargement of brain size, seen in species such as Homo habilis, combined with evidence of tool use, implies increased dexterity and cognitive abilities. The evolution of bipedalism might have been driven by several factors, including effectiveness in thermoregulation by exposing more of the body's surface, energy efficiency, and the freedom to use hands for carrying various objects, as suggested by the diverse range of hypotheses that account for such an evolutionary leap.
The study of fossils also provides insights into dietary changes, disease, and sometimes social behavior, even though the latter often requires additional evidence beyond paleontological findings. Anthropologists often have to fill in gaps with educated speculation, as the fossil record is incomplete and cannot always accurately convey the intricacies of hominid life. However, significant finds like those of Homo habilis provide valuable clues in piecing together the story of human evolution.