For another meaning of the word Primate, see Primate (religion).
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All primates exhibit pentadactyly (they have five fingers), 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. In this context, this mosaic of features was useful for grasping branches, especially mid-sized ones no thicker than three inches in diameter. Forward-facing color binocular vision was also useful for our brachiating ancestors, 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.
In many primate species, the males are larger than the females. The following is a table in kilogram (kg), pound (lb), gram (g), and ounce (oz).
| Species | Female | Male |
|---|---|---|
| Gorilla | 105 kg (231 lb) | 205 kg (452 lb) |
| Human | 52 kg (114 lb) | 75 kg (165 lb) |
| Patas monkey | 5.5 kg (12 lb) | 10 kg (22 lb) |
| Proboscis Monkey | 9 kg (20 lb) | 19 kg (42 lb) |
| Pygmy marmoset | 120 g (4.2 oz) | 140 g (5 oz) |
It will be noted that all but one of these are Old World species, and that sexual dimorphism is much less in the marmoset (New World) than in the other species listed. New World monkeys are typically much less sexually dimorphic than the Old World monkeys and apes. Correspondingly, they frequently form pair bonds, whereas many Old World species are polygynous.
