ABSTRACT
The highest taxon that distinguishes New World monkeys is the Platyrrhini. The descriptions of platyrrhines behavior are arranged under four headings: ecology, sociality, life cycle, and cognition. Platyrrhines occur from Mexico through South America. They are highly arboreal and the prominence of loud calls and olfactory communication are probably related to dense forest habitats. With regard to color vision platyrrhines display both dichromatic and trichromatic phenotypes, differentiated by sex. Functional research indicates that both can be advantageous in various circumstances. Relatively large neonates affect reproductive patterns. Encephalization is associated with varied social and ecological challenges. The typical gestation length of about five months correlates roughly with the relatively small maternal body masses of most New World species. An important feature of primate evolution is expansion of the brain. The Expensive Tissue Hypothesis (ETH) proposed that evolution of an energetically expensive large brain must be compensated by reduction of other expensive tissue such as the digestive tract.
