8.3: The Anthropoid Suborder

General Anthropoid Features

When the two primate suborders split from one another, prosimians retained more ancestral traits while anthropoids developed more derived traits, which are discussed below. As mentioned earlier, anthropoids have better vision than prosimians and therefore have more protection for their eyes, as demonstrated by full postorbital closure protecting the more convergent eyes that anthropoids possess (with one exception as seen in Figure 8.3.1.3).

Most anthropoids are trichromatic, and all have a fovea, a depression in the retina at the back of the eye containing concentrations of cells that allows them to see things very close up in great detail. The heavier reliance on vision over olfaction is also reflected in the shorter snouts ending with the dry nose of haplorrhine primates, the scientific name for the anthropoids. The vast majority of these primates are diurnal—active during the day, so this group lacks the tapetum lucidum that is so useful to nocturnal species. On average, anthropoids also have larger brains relative to their body size when compared with prosimians.

The Anthropoids differ from the Prosimians in their ecology and behavior as well. Anthropoids are generally larger and they tend to be leaf and fruit eaters. This dietary difference is reflected in their teeth, which are broader with more surface area for chewing. The larger body size of this taxon also influences locomotion. Only one species is a vertical clinger and leaper. Most members of this suborder are quadrupedal, with one subgroup specialized for brachiation.

A few anthropoid taxa are monomorphic, meaning males and females are the same size, but many members of this group show moderate to high sexual dimorphism in body size and canine size. Anthropoids also differ in social behavior. All but two species live in groups, which is very different from the primarily solitary prosimians. Differences between the two suborders are summarized below.

The Anthropoid is divided into three infraorders: Tarsiiformes, which includes the tarsiers of Asia; Platyrrhini (New World monkeys), which includes the monkeys of Central and South America; and Catarrhini (Old World monkeys), a group that includes the monkeys of Asia and Africa, apes, and humans. According to molecular estimates, tarsiers split from the other anthropoid primates close to 70 million years ago, and platyrrhines split from catarrhines close to 46 million years ago (Pozzi et al. 2014).

A note about terminology: The terms “Old World” monkeys and “New World” monkeys come from a colonial worldview. “Old World” referred to Europe, Asia and Africa, while “New World” referred to the Americas as seen through the eyes of European colonizers. Most primatologists today consider these terms outdated and rooted in colonialism. Even so, they remain useful shorthand because they highlight both the distinct evolutionary histories and geographic ranges of these two groups. For that reason, we’ll continue using them throughout the text, but will also include references to their scientific, taxonomic names.