Final answer:
The evidence of a skeleton being biped includes a femur with a valgus angle, evolved spinal curves, an arched foot, and aligned toes for effective weight transmission during bipedal locomotion. Fossilized footprints, like those found at Laetoli by Mary Leakey, also provide strong evidence of early bipedalism in hominins.
Step-by-step explanation:
One of the clearest indications that a skeleton was biped can be found in certain key anatomical structures. For example, the presence of a valgus angle in the femur which positions the knee and foot under the pelvis, the development of spinal curves that balances the upper body, and the evolution of an arched foot with a big toe aligned with the other toes are all crucial for bipedal locomotion. The discoveries of early hominin fossils, like the renowned Laetoli footprints discovered by Mary Leakey, which exhibit a modern striding gait, provide substantial evidence that Australopithecus afarensis was capable of bipedal walking approximately 3.5 million years ago.
The skeletal features of bipedal creatures undergo adaptation to support walking on two legs. Changes such as these, observed in hominin fossils, are foundational in understanding the evolution of bipedalism among early human ancestors.