- For the ecclesiastical use of this term, see primate (religion)
A primate is any member of the biological order Primates, the group that contains all lemurs, monkeys, and apes, including humans. The English singular primate is a back-formation from the Latin name Primates, which itself was the plural of the Latin primas ("one of the first, excellent, noble"). Colin Groves lists about 350 species of primates in Primate Taxonomy.
All primates have five fingers (pentadactyly), a generalized dental pattern, and a primitive (unspecialized) body plan. Another distinguishing feature of primates is fingernails. Opposing thumbs are also a characteristic primate feature, but are not limited to this order; opossums, for example, also have opposing thumbs. In primates, the combination of opposing thumbs, short fingernails (rather than claws) and long, inward-closing fingers is a relic of the ancestral practice of brachiating through trees. Forward-facing color binocular vision was also useful for the brachiating ancestors of humans, particularly for finding and collecting food. All primates, even those that lack the features typical of other primates (like lorises), share eye orbit characteristics that distinguish them from other taxonomic orders.
As the table below illustrates, in many primate species, the males are larger than the females. However this picture is incomplete. All but one of these are Old World species, and in this group the mating system is usually polygynous; sexual dimorphism is expected with this kind of social structure. As the table shows, sexual dimorphism is much less in the marmosets (New World) than in the other species listed, and this is characteristic of New World monkeys in comparison with the Old World monkeys and apes. This is because the New World monkeys generally form pair bonds.
Classification and evolution
The Primate order lies in a tight clustering of related orders (the Euarchontoglires) within the Eutheria, a subclass of Mammalia. Recent molecular genetic research on primates, flying lemurs, and tree shrews has shown that the two species of flying lemur (Dermoptera) are more closely related to the primates than the tree shrews of the order Scandentia, even though the tree shrews were at one time considered primates. These three orders make up the Euarchonta clade. This clade combines with the Glires clade (made up of the Rodentia and Lagomorpha) to form the Euarchontoglires clade. Variously, both Euarchonta and Euarchontoglires are ranked as superorders.
| |--rodents (Rodentia)
| \--rabbits, hares, pikas (Lagomorpha)
|--tree shrews (Scandentia)
|--flying lemurs (Dermoptera)
In modern, cladistic reckonings, the Primate order is also a true clade. The suborder Strepsirrhini, the "wet-nosed" primates, split off from the primitive primate line about 63 million years ago. The seven strepsirhine families are the four related lemur families and the three remaining families that include the lorises, the Aye-aye, the galagos, and the pottos. Some classification schemes wrap the Megaladapidae into the Lemuridae and the Galagonidae into the Loridae, yielding a three-two family split instead of the four-three split as presented here.
The Aye-aye is difficult to place in Strepsirrhini. Its family, Chiromyiformes, could be a lemuriform primate and its ancestors split from lemur line more recently than the lemurs and lorises split, about 50 mya. Otherwise it is sister to all of the other strepsirrhines, in which case in evolved away from the main strepsirrhine line between 50 and 63 mya.
The suborder Haplorhini, the "dry-nosed" primates, is composed of two sister clades. The prosimian tarsiers in family Tarsiidae (monotypic in its own infraorder Tarsiiformes), represent the most primitive division at about 58 mya. The Simiiformes contain the two unranked clades the New World monkeys in one, and the Old World monkeys, humans and the other apes in the other. This division happened about 40 mya.
In older classifications, the Primates were divided into two superfamilies: Prosimii and Anthropoidea. The Prosimii included all of the prosimians: all of Strepsirrhini plus the tarsiers. The Anthropoidea contained all of the simians.
Primate Taxonomy (Smithsonian Institute Press, 2001), Colin Groves (ISBN 156098872X)
Primates in Question (Smithsonian Institute Press, 2003), Robert W. Shumaker & Benjamin B. Beck (ISBN 1-58834-176-3)
Last updated: 10-11-2005 02:06:03