Simian

Taxonomy

In earlier classification, New World monkeys, Old World monkeys, apes, and humans – collectively known as simians or anthropoids – were grouped under Anthropoidea (; from Ancient Greek ἄνθρωπος (ánthrōpos) 'human' and -οειδής (-oeidḗs) 'resembling, connected to, etc.'), while the strepsirrhines and tarsiers were grouped under the suborder "Prosimii". Under modern classification, the tarsiers and simians are grouped under the suborder Haplorhini, while the strepsirrhines are placed in suborder Strepsirrhini. Strong genetic evidence for this is that five SINEs are common to all haplorhines whilst absent in strepsirrhines — even one being coincidental between tarsiers and simians would be quite unlikely. Despite this preferred taxonomic division, "prosimian" is still regularly found in textbooks and the academic literaturebecause of familiarity, a condition likened to the use of the metric system in the sciences and the use of customary units elsewhere in the United States. In the Anthropoidea, evidence indicates that the Old World and New World primates went through parallel evolution.

Primatology, paleoanthropology, and other related fields are split on their usage of the synonymous infraorder names, Simiiformes and Anthropoidea. According to Robert Hoffstetter (and supported by Colin Groves), the term Simiiformes has priority over Anthropoidea because the taxonomic term Simii by van der Hoeven, from which it is constructed, dates to 1833. In contrast, Anthropoidea by Mivart dates to 1864, while Simiiformes by Haeckel dates to 1866, leading to counterclaims of priority. Hoffstetter also argued that Simiiformes is also constructed like a proper infraorder name (ending in "iformes"), whereas Anthropoidea ends in -"oidea", which is reserved for superfamilies. He also noted that Anthropoidea is too easily confused with "anthropoïdes", which translates to "apes" from several languages.

Some lines of extinct simian also are either placed into the Eosimiidae (to reflect their Eocene origin) and sometimes in Amphipithecidae, thought to originate in the Early Oligocene. Additionally, Phileosimias is sometimes placed in the Eosimiidae and sometimes categorised separately.

Evolution

The origin of anthropoid primates is primarily thought by scientists to have been in Africa. However, there is also a competing theory suggesting that they may have originated in Asia during the middle to late Eocene, having crossed the Tethys Sea on natural rafts or floating islands alongside other Asian mammals.

The New World monkeys in parvorder Platyrrhini split from the rest of the simian line about 40 million years ago (mya), leaving the parvorder Catarrhini occupying the Old World. This latter group split about 25 mya between the Cercopithecidae and the apes, making Cercopithecidae more closely related to the apes than to the Platyrrhini.

Classification

The following is the listing of the various simian families, and their placement in the order Primates:

• Order Primates
  • Suborder Strepsirrhini: nontarsier prosimians
  • Suborder Haplorhini: tarsiers and monkeys, including apes
    • Infraorder Tarsiiformes
    • Infraorder Simiiformes
      • Parvorder Platyrrhini: New World monkeys
        • Family Callitrichidae: marmosets and tamarins
        • Family Cebidae: capuchins and squirrel monkeys
        • Family Aotidae: night or owl monkeys (douroucoulis)
        • Family Pitheciidae: titis, sakis, and uakaris
        • Family Atelidae: howler, spider, and woolly monkeys
      • Parvorder Catarrhini
        • Superfamily Cercopithecoidea: Old World monkeys
          • Family Cercopithecidae
        • Superfamily Hominoidea
          • Family Hylobatidae: gibbons
          • Family Hominidae: great apes, including humans
      • †Amphipithecidae
      • †Eosimiidae
      • †Aseanpithecus

Below is a cladogram with some of the extinct simian species with the more modern species emerging within the Eosimiidae. The simians originated in Asia, while the crown simians were in Afro-Arabia. It is indicated approximately how many Mya the clades diverged into newer clades.

Usually the Ekgmowechashalidae are considered to be Strepsirrhini, not Haplorhini. A 2018 study places Eosimiidae as a sister to the crown haplorhini. In 2020 papers, the Proteopithecidae are part of the Parapithecoidea, and Nosmips aenigmaticus (previously in Eosimidae) is a basal simian. In a 2021 paper, the following basal simians were found:

Dolichocebus annectens and Parvimico materdei would normally, given their South American location and their age and other factors, be considered Platyrrhini. The original Eosmiidae appear polyphyletic with Nosmips, Bahinia, and Phileosimias at different locations from other eosimians.