A catarrhine refers to a major group of primates, classified scientifically as the infraorder Catarrhini. This diverse group encompasses all Old World monkeys, apes, and humans. Understanding catarrhines provides insights into primate evolution and their distinct physical characteristics.
Key Distinguishing Features
Catarrhines possess distinct anatomical features that differentiate them from their primate relatives, particularly New World monkeys (platyrrhines). Their name, “catarrhine,” derives from Greek words meaning “downward-nosed,” reflecting their distinct nose structure. Their nostrils are narrow, close together, and point downwards, contrasting with the wide, flat, outward-facing nostrils of platyrrhines.
Another distinguishing feature is their dental formula. Catarrhines consistently exhibit a 2.1.2.3 dental pattern: two incisors, one canine, two premolars, and three molars in each jaw quadrant, totaling 32 teeth. Most platyrrhines, in comparison, have a 2.1.3.3 dental formula, possessing an additional premolar.
The presence and function of tails also vary significantly between catarrhines and other primate groups. No catarrhine species possesses a prehensile, or grasping, tail. While many Old World monkeys retain tails, these are used for balance during movement and cannot grip branches or objects. Apes and humans, which are also catarrhines, lack external tails entirely.
Geographic Distribution and Habitat
Catarrhines are found natively across the continents of Africa and Asia, commonly referred to as the “Old World.” Their natural distribution showcases a wide array of environments. Baboons, for instance, inhabit the open savannas of Africa, while macaques are widespread throughout various Asian forests.
Tropical rainforests across both continents are home to many ape species, demonstrating their adaptability to dense forest canopies. This broad geographic range highlights the diverse habitats catarrhines successfully occupy, from arid landscapes to lush jungle environments. Humans, as members of the catarrhine group, represent an exception, having expanded their distribution across virtually every biome globally.
The Catarrhine Family Tree
The catarrhine group is broadly divided into two main superfamilies: Cercopithecoidea, which encompasses Old World monkeys, and Hominoidea, consisting of apes and humans. Each superfamily has its own set of characteristics that reflect their evolutionary paths.
The Cercopithecoidea, or Old World monkeys, include well-known primates such as baboons, macaques, colobus monkeys, and langurs. These monkeys typically have non-prehensile tails, though tail length can vary greatly among species. They are characterized by bilophodont molars, which feature four cusps arranged in two parallel pairs. Many species also exhibit prominent ischial callosities, which are hardened patches of skin on their buttocks that provide support when sitting.
The Hominoidea superfamily comprises all apes and humans, distinguished by the complete absence of an external tail. This group includes the smaller gibbons, often referred to as “lesser apes,” and the larger “great apes” like orangutans, gorillas, and chimpanzees. Humans are also classified within the great ape lineage. Hominoids generally possess a larger brain-to-body size ratio compared to Old World monkeys and are characterized by Y-5 molars, where five cusps are separated by a Y-shaped groove.