Final answer:
Ardipithecus ramidus is considered a hominin due to its bipedal traits, such as the forward position of the foramen magnum and the absence of weight-bearing upper arm bones. Other characteristics, such as thin dental enamel and an opposable big toe, suggest bipedalism on the ground and quadrupedalism in trees. Fossil discoveries in forested environments further support this hypothesis.
Step-by-step explanation:
Ardipithecus ramidus can be considered a hominin due to several reasons. First, the forward position of the foramen magnum suggests bipedalism, indicating that Ardipithecus walked on two legs. Additionally, the smaller size of its upper arm bones suggests that they were not used for weight-bearing during locomotion.
Ardipithecus also possesses traits such as thin dental enamel, a reduced canine, and an opposable big toe. These traits suggest that it was bipedal on the ground and quadrupedal in the trees.
Moreover, the discovery of Ardipithecus fossils in heavily forested environments supports the hypothesis that it was adapted for both tree-dwelling and bipedal walking on the ground.