Final answer:
The primate anatomical characteristic that is a symplesiomorphy shared with non-primate mammals is the presence of five digits on each limb.
Step-by-step explanation:
The following primate anatomical characteristic that is a symplesiomorphy shared with non-primate mammals is having five digits. A symplesiomorphy refers to an ancestral trait that is shared by two or more taxa. In this context, both primates and non-primate mammals typically have five fingers or toes on each limb, which is a trait inherited from a common ancestor. Other options such as an enlarged brain, a tooth comb, fused mandibular symphysis, and bipedal locomotion are either unique adaptations found in primates or derived features that separate primates from other mammals.