Final answer:
The Laetoli footprints provide evidence that Australopithecus afarensis was bipedal. Other hominin species like Homo erectus and Ardipithecus, also show adaptations for bipedalism, supporting the savanna hypothesis that upright walking evolved as an adaptation to environmental changes in the Pliocene.
Step-by-step explanation:
The archaeological site of Laetoli provides archaeological evidence that Australopithecus afarensis was bipedal. This conclusion is drawn from the discovery of a 75-foot trail of footprints in East Africa, by the paleoanthropologist Mary Leakey in the 1980s. These footprints, dated to about 3.5 million years ago (MYA), suggest a modern striding gait, indicating that these early hominins were well adapted to walking on two legs.
Fossils of other hominin species such as Ardipithecus from the Pliocene era, and later, species like Homo erectus, also show adaptations for bipedal locomotion. Adaptations such as a broader pelvis, longer legs, and arched feet in early Homo species, as compared to quadrupedal primates, denote an evolutionary progression towards efficient bipedalism. These changes occurred despite differences that persisted in their anatomy, such as larger jaws, teeth, and smaller brain size relative to modern humans.
Even H. floresiensis, though not as anatomically similar to modern humans, exhibited bipedal traits. The skeletal remains show that despite having thick leg bones and no chin, they also were capable of walking upright, albeit with a distinct gait. Such evidence collectively supports the hypothesis that many human traits, including upright bipedalism, evolved as adaptations to changing environments during the Pliocene, a time marked by colder climates and savanna expansion according to the savanna hypothesis.