Simiiformes

Simiiformes, commonly called simians, is a clade of primates that includes the monkeys, apes, and humans, along with their extinct relatives. It lies within the suborder Haplorhini and is typically treated as an infraorder or parvorder that comprises two major divisions: Platyrrhini (New World monkeys) and Catarrhini (Old World monkeys and apes, including humans). Within Catarrhini, the traditional groups are Cercopithecoidea (Old World monkeys) and Hominoidea (apes and humans).

Geographically and taxonomically, Platyrrhini are native to the Americas, while Catarrhini are found in Africa and Asia. The two parvorders, Platyrrhini and Catarrhini, are believed to have diverged from a common simian ancestor around 40 to 45 million years ago, with the later split giving rise to the lineages that produced the Old World monkeys, apes, and humans.

Key characteristics of Simiiformes include relatively large brains for body size, forward-facing eyes with stereoscopic vision, and a tendency toward reduced reliance on the sense of smell compared with more primitive primates. Dental formulas vary by lineage: Platyrrhini typically exhibit a 2-1-3-3 formula, while Catarrhini usually show a 2-1-2-3 formula. Members of this clade also display broader social systems, advanced learned behaviors, and a range of locomotor adaptations.

The clade encompasses a vast diversity of living species, from small platyrrhine monkeys to large hominoids such as orangutans, gorillas, chimpanzees, and humans. It is a central focus of studies in primatology, evolution, and comparative anatomy.