Final answer:
Prosimians, a group of primates, are generally smaller, with smaller brains compared to anthropoids, and many are nocturnal. They have five fingers with an opposable thumb, several types of teeth, and a postorbital bar. They also have larger olfactory centers in their brains, highlighting their reliance on smell.
Step-by-step explanation:
The physical features of prosimians, a sub-group of primates, include several distinctive characteristics. Prosimians, such as bush babies, lemurs, lorises, pottos, and tarsiers, tend to have smaller brains and bodies compared to anthropoids, with many being nocturnal. Prosimians are characterized by having pentadactyl limbs (five fingers), which often include an opposable thumb, allowing for a strong grip and the ability to hold objects.
Another notable feature of prosimians is their dentition, possessing several types of teeth suited to a varied diet. Prosimians have a postorbital bar, a bone that runs around the eye socket, which is a trait shared with other primates. Furthermore, prosimians typically exhibit larger olfactory centers in their brains, indicative of their reliance on sense of smell, which contrasts with the more visually oriented anthropoids.
While some prosimians like tarsiers are placed in the Haplorhini group or 'dry-nosed' primates, most other prosimians are part of the Strepsirrhini or 'wet-nosed' primates, which generally have a smaller size and brain than their dry-nosed relatives. Moreover, their physical adaptations, such as the capability to make vitamin C, reflect their distinct ecological niches and dietary needs.