simians

Simians are a clade of primates that includes most monkeys and all apes, including humans. In modern taxonomy, the group Simiiformes is divided into two major lineages: Platyrrhini, the New World monkeys, and Catarrhini, which comprises Old World monkeys and the apes. Simians are distinguished from more primitive primates by features such as a larger brain relative to body size, a greater reliance on vision with forward-facing eyes, and more complex social behaviors.

The group is diverse in size, form, and ecology. It ranges from small marmosets and tamarins to large apes such as gorillas, chimpanzees, and humans. Locomotion includes arboreal quadrupedalism, suspensory brachiation in some species, and knuckle-walking in others. Diets are broadly omnivorous, including fruits, leaves, seeds, and insects. Platyrrhines are native to the Americas, while catarrhines inhabit Africa and Asia and include both Old World monkeys and the apes.

Simians are believed to have originated in the early Cenozoic, with the split between platyrrhines and catarrhines occurring roughly 40 to 45 million years ago. They exhibit a wide range of social structures and life histories, contributing to their ecological and evolutionary prominence across tropical forests and other habitats.

Conservation concerns affect many simian species, threatened by habitat loss, hunting, and disease. They play important ecological roles as seed dispersers, pollinators, and insect predators, and they have significant value for scientific research and human culture.