Which feature is characteristic of haplorrhines?

The characteristic feature of haplorrhines is the presence of nails instead of claws. Haplorrhines, which include tarsiers, monkeys, apes, and humans, exhibit adaptations that are indicative of their evolutionary lineage towards increased reliance on vision and complex social behaviors. The presence of nails allows for a more precise grip and manipulation of objects compared to claws, which is an essential feature for many haplorrhine species that engage in intricate foraging strategies and social interactions.

This trait reflects the evolutionary adaptations of haplorrhines towards a more arboreal lifestyle and a diet that often includes a variety of foods requiring dexterity. Additionally, the presence of nails is associated with a shift in locomotion and behavior that differentiates them from strepsirrhines, who possess a dental tooth comb (an adaptation for grooming) and a moist rhinarium (the wet nose commonly seen in some mammalian species). The post-orbital bar is a bony structure found in several primate groups, but it is not unique to haplorrhines, as some other primate branches exhibit this feature as well. Thus, the presence of nails stands out as a clear and defining characteristic of haplorrhines.