Catarrhini

Catarrhini is a major parvorder within the infraorder Simiiformes, encompassing Old World monkeys, apes, and humans. Members of this clade share distinctive anatomical traits such as downward‑facing nostrils, a narrow nasal septum, and a dental formula of 2.1.2.3. Catarrhines typically exhibit trichromatic vision, robust postcranial morphology, and complex social structures supported by extended developmental periods.

Evolution

Catarrhines diverged from Platyrrhini approximately 35- 40 million years ago. Early catarrhines were small arboreal primates inhabiting Afro‑Arabian forests. Subsequent radiations produced two major lineages: Cercopithecoidea (Old World monkeys) and Hominoidea (apes and humans). Hominoids underwent significant morphological changes, including loss of the tail, expansion of the shoulder girdle, and increased encephalization.

Cercopithecoidea (Old World Monkeys)

Includes baboons, macaques, colobus monkeys, and related taxa. Cercopithecoids often exhibit terrestrial or semi‑terrestrial adaptations and possess bilophodont molars.

Hominoidea (Apes and Humans)

Includes gibbons, great apes, and Homo sapiens. Hominoids show increased brain size, diverse locomotor strategies, and prolonged developmental periods.

Anatomy

Catarrhines are defined by several key anatomical features:

• Downward‑facing nostrils and narrow nasal septum
• Dental formula 2.1.2.3
• Trichromatic color vision in many species
• Y‑5 molar pattern in hominoids; bilophodont molars in cercopithecoids
• Strong limb bones and versatile locomotor adaptations

These traits distinguish Catarrhini from Platyrrhini, which possess outward‑facing nostrils, a 2.1.3.3 dental formula, and generally lack trichromacy.

Classification Table