Final answer:
Members of the genus Paranthropus, which included robust hominins with large teeth suited for a coarse vegetarian diet, are not considered ancestors of modern humans due to their specialized dentition and dietary focus.
Step-by-step explanation:
The members of the genus Paranthropus are not considered possible ancestors to modern humans primarily because they exhibit the derived characteristic of large teeth that modern humans do not share. This genus includes Paranthropus robustus, Paranthropus aethiopicus, and Paranthropus boisei. They were muscular, with heavy wear on their molars indicating a coarse, fibrous vegetarian diet. Although all hominins, including Paranthropus and Homo, share traits like bipedalism, the specialized dentition and dietary focus of Paranthropus is distinct and does not align with the evolutionary pathway that led to modern humans.