Final answer:
The development of bipedalism was indeed associated with the expansion of savanna habitats in East Africa, which is evidenced by the savanna hypothesis and supported by the discovery of the Laetoli footprints by Mary Leakey.
Step-by-step explanation:
The statement that the development of bipedalism was associated with the expansion of open grassland or savanna habitats in East Africa is A True. The savanna hypothesis suggests that many human traits, such as upright bipedalism, evolved as adaptations to a savanna habitat. Hominins, the early human ancestors, developed bipedalism that allowed them to move more efficiently across the savanna, possibly to follow migratory herds, reach food sources, or improve thermoregulation. Mary Leakey's discovery of the Laetoli footprints supports the idea that bipedalism was already present in hominins like Australopithecus afarensis around 3.5 million years ago, further evidencing the link between bipedalism and the savanna environment.