Final answer:
The last common ancestor proposed for living African apes and humans is Sahelanthropus tchadensis, not one of the given options. Sahelanthropus lived around 7 million years ago during the time the two lineages diverged.
Step-by-step explanation:
This species lived approximately 7 million years ago (MYA), aligning with the period when humans and chimpanzees diverged, according to genetic studies. However, it's important to note that the foramen magnum of Sahelanthropus suggests it may not have been bipedal, differentiating it from later hominins. In contrast, Ouranopithecus, which is mentioned among the choices, has been identified as a possible ancestor to modern African apes based on its facial morphology.
When discussing the common ancestry of humans and great apes, it is invaluable to understand the term hominin, which designates species more closely related to humans than to chimpanzees post the primate lineage split. Bipedal hominins like Australopithecus, Homo habilis, and Homo erectus are seen as part of the human lineage, and they display significant evolutionary markers that distinguish humans, such as upright posture and larger brain size.