Final answer:
The statement that Orrorin tugenensis's bipedalism was mainly for walking on branches with arms used for balance is likely false. Fossil evidence suggests Orrorin was more adapted for bipedal ground walking, although with some potential arboreal traits.
Step-by-step explanation:
Orrorin tugenensis is an early hominin species that provides evidence for bipedalism around 6 million years ago. The fossil evidence suggests that Orrorin's femoral anatomy is more aligned with bipedalism than with quadrupedal motion. This is reinforced by the larger femoral head used to support the upper body weight, as well as adaptations in the teeth such as thick dental enamel and small, square molars similar to modern humans.
Contrary to offerings like H. floresiensis, which may have had a different form of bipedalism due to anatomical differences, Orrorin shares more similarities with modern human bipedality. Although there has been speculation on whether Orrorin's bipedalism involved walking on branches and using arms for balance, current evidence infers direct bipedal movement on the ground.
A comparison with other hominin species like Ardipithecus ramidus and Australopithecus afarensis reveals a spectrum of locomotion where bipedalism was common, yet it could coexist with arboreal traits, suggesting a complex evolution of bipedal habits. Considering the evidence, the claim that Orrorin tugenensis's bipedalism was primarily for walking on branches using arms for balance is likely false, as the fossils hint at bipedalism adapted for ground walking, despite potentially retaining some ability for arboreal locomotion.