Final answer:
The primate anatomical characteristic that is a symplesiomorphy shared with Non primate mammals is having five fingers on each hand and five toes on each foot.
Step-by-step explanation:
Among the options provided, five fingers on each hand and five toes on each foot is the symplesiomorphy shared with nonprimate mammals. This term refers to an ancestral trait that is found both within the group in question - in this case, primates - and in other groups that do not share the more recent common ancestry. Primates, including humans, do exhibit several key anatomical features such as opposable thumbs and, in many nonhuman species, opposable big toes; flat nails instead of claws; and enlarged brains. However, the number of digits is a more ancient trait found in a wider variety of mammals, making it a symplesiomorphy. Other features like the tooth comb and fused mandibular symphysis are unique adaptations not shared with Non primate mammals.