狭鼻小目小目

狭鼻小目的动物鼻孔都是狭窄及向下的。它们不像阔鼻小目，一般都是白天活动，而尾巴并非卷尾。它们的指甲都是扁平的，上下齿式都是2.1.2.3。

狭鼻小目大部分物种都是两性异形的，且大都不是一夫一妻的。很多但不是全部物种都以群族方式生活。它们是非洲及亚洲的原住民。

分类及演化

猿及旧世界猴于4000万年前从新世界猴中分裂出来。主要的狭鼻小目于2500万年前出现，而于1800万年前长臂猿科从人科中分支出来。

• 狭鼻小目 Catarrhini
• †渐新猿科 Oligopithecidae
• †原上猿总科 Propliopithecoidea
• †原上猿科 Propliopithecidae
• †上猿总科 Pliopithecoidea
• †醉猿科 Dionysopithecidae
• †上猿科 Pliopithecidae
• †科 Crouzeliinae
• †树猿总科 Dendropithecoidea
• †树猿科 Dendropithecidae
• †总科/超科 Saadanioidea
• †萨丹猴科 Saadaniidae
• †总科/超科 Parapithecoidea
• †副僧面猴科 Parapithecidae
• 猴总科 Cercopithecoidea
• 猴科 Cercopithecidae
• 人猿总科 Hominoidea
• †原康修尔猿科 Proconsulidae
• †非洲古猿科 Afropithecidae
• 长臂猿科 Hylobatidae
• 人科 Hominidae

The parvorder Catarrhini (known commonly as catarrhine monkeys, Old World anthropoids, or Old World monkeys) consists of the Cercopithecoidea (Old World monkeys) and Hominoidea (apes). In 1812, Geoffroy grouped those two groups together and established the name Catarrhini, "Old World monkeys" (singes de l'Ancien Monde in French). Its sister in the infraorder Simiiformes (simians) is the parvorder Platyrrhini (New World monkeys). There has been some resistance to directly designate apes (and thus humans) as monkeys despite the scientific evidence, so "Old World monkey" may be taken to mean the Cercopithecoidea or the Catarrhini. That apes are monkeys was already realized by Georges-Louis Leclerc, Comte de Buffon in the 18th century. Linnaeus placed this group in 1758, together with what we now recognise as the tarsiers and the New World monkeys, in a single genus "Simia" (sans Homo). The Catarrhini are all native to Africa and Asia. Members of this parvorder are called catarrhines.

The Catarrhini are the sister group to the New World monkeys, the Platyrrhini. Some six million years before the ape-Cercopithecoidea bifurcation, the Platyrrhini emerged within "monkeys" by migration to South America from Afro-Arabia (the Old World), likely by ocean.

Description

The technical distinction between the New World platyrrhines and Old World catarrhines is the shape of their noses. The platyrrhines (from Ancient Greek platy-, "flat", and rhin-, "nose") have nostrils which face sideways. The catarrhines (from Ancient Greek katà-, "down", and rhin-, "nose") have nostrils that face downwards. Catarrhines also never have prehensile tails, and have flat fingernails and toenails, a tubular ectotympanic (ear bone), and eight, not 12, premolars, giving them a dental formula of 2.1.2.32.1.2.3, indicating 2 incisors, 1 canine, 2 premolars, and 3 molars on each side of the upper and lower jaws.

Most catarrhine species show considerable sexual dimorphism and do not form a pair bond. Most, but not all, species live in social groups. Like the platyrrhines, the catarrhines are generally diurnal, and have grasping hands and (with the exception of bipedal humans) grasping feet.

The apes—in both traditional and phylogenic nomenclature—are exclusively catarrhine species. In traditional usage, ape describes any tailless, larger, and more typically ground-dwelling species of catarrhine. "Ape" may be found as part of the common name of such species of monkeys, such as the Barbary ape and Black ape. In phylogenic usage, the term ape applies only to the superfamily Hominoidea. This grouping comprises two families: Hylobatidae, the lesser apes (gibbons); and Hominidae, the great apes, including orangutans, gorillas, chimpanzees, humans, and related extinct genera, such as the prehuman australopithecines and the giant orangutan relative Gigantopithecus.

Classification and evolution

According to Schrago & Russo, New World monkeys split from their Old World kin about 35 million years ago (Mya). They use the major catarrhine division between cercopithecoids and hominoids of about 25 Mya (which they argue is strongly supported by the fossil evidence), as a calibration point, and from this also calculate the gibbons separating from the great apes (including humans) about 15-19 Mya.

According to Begun and Harrison, the Catarrhini split from their New World monkey kin about 44 - 40 Mya, with the first catarrhines appearing in Africa and Arabia, and not appearing in Eurasia (outside Arabia) until 18-17 Mya.

Catarrhini lost the enzyme Alpha-galactosidase, present in all other mammal lineages, sometime after the split from platyrrhini. It is hypothesized that an ancient pathogen containing Alpha-galactosidase may be responsible, as only individuals with mutations that "turned off" the gene for Alpha-galactosidase would have produced antibodies against the pathogen and survived.

The distinction between apes and monkeys is complicated by the traditional paraphyly of monkeys: apes emerged as a sister group of Old World monkeys in the catarrhines, which are a sister group of New World monkeys. Therefore, cladistically, apes, catarrhines and related contemporary extinct groups such as Parapithecidae are monkeys as well, for any consistent definition of "monkey". "Old World Monkey" may also legitimately be taken to be meant to include all the catarrhines, including apes and extinct species such as Aegyptopithecus, in which case the apes, Cercopithecoidea and Aegyptopithecus emerged within the Old World Monkeys.