Catarrhines are a group of primates that include Old World monkeys, apes, and humans. They are characterized by their downward-facing nostrils and typically have a more complex social structure compared to other primates. Catarrhines are primarily found in Africa and Asia. This group is divided into two main subfamilies: Cercopithecoidea, which includes Old World monkeys, and Hominoidea, which includes apes and humans. Catarrhines generally have larger body sizes and more advanced cognitive abilities than their New World monkey counterparts, making them an important subject of study in primatology.