Primates all have heterodont dentition. This means the teeth are not all the same. Primates possess different teeth used for different functions. These teeth are:
Incisor: tooth designed for cutting
Canine: tooth with pointed cusps for tearing and incising
Premolars: teeth with broad occlusal (top) cusps for grinding and reducing food material as an aid to digestion
Molars: same as premolars but with broader occlusal surfaces
In primates, as in all toothed mammals, the dentition of each side of the jaw is a mirror of that on the other side. Therefore it is sufficient to describe only half of the dentition of the upper and lower jaw. However the number of teeth in the upper and lower jaws may differ, so each must be counted. To count dentition, start at the incisors and count around towards the back of the jaw.
The teeth are counted like this:
Incisors-canine-premolars-molars
Incisors-canine-premolars-molars
The upper jaw is on top and the lower jaw is on the bottom.
Counting these teeth results in a dental formula . Primates can be identified by their unique dental formula. Primates have lost a premolar and an incisor in comparison with other mammals, so a primate dentition will look something like 2133 or 2123
2133 2123
Most other mammals have three incisors per side and four or five premolars.
One special primate feature found in Strepsirhine primates is the dental comb . The dental comb is formed from the procumbent (tilted forward) incisors and canines on the lower jaw. Often, when there is a dental comb, the 1 st premolar takes over the function and shape of a canine. It is then referred to as caniniform.
Other features:
It is also useful to look at the cusp pattern of molars. The cusps can have a bilophodont , non- bilophodont , or Y-5 pattern (see p. 96 in your book). Bilophodont molars have 4 cusps, arranged in two pairs and are characteristic of Catarrhine monkeys. Y-5 molars have 5 cusps arranged in a y pattern and are characteristic of humans and apes.
You should also know the diastema , a space in the toothrow that accommodates one or more teeth in the opposite jaw when the mouth is closed.

Crania:
You can also differentiate amongst primates and between primates and other mammals by looking at their crania. Here are a few traits that will be useful for this purpose:
Prognathic: having the lower face and jaws projecting in front of the upper parts of the face, having a protruding snout
Orthognathic: The opposite of prognathic, having a flatter, less protruding snout
Dental arcade: This is the shape of the upper toothrow along the palate. Monkeys and apes have a U-shaped or rectangular dental arcade. Humans have a parabolic dental arcade (p. 193 in your book).
Supraorbital tori: Also known as the brow ridge. A continuous ridge of bone in the skull, curving over each eye and connected across the bridge of the nose.
Sagittal crest: a ridge of bone running along the top of the skull which anchors the jaw muscles.
Classification:
Primate classification can either be grade or clade based. Grade based classifications are those such as Anthropoid vs. prosimian . They are not based on evolutionary relationships, but on arbitrarily defined differences and silimarities. Clade based classifications group organisms based on shared derived traits, with the aim of identifying groups of organisms descended from a common ancestor.
This table shows some characteristics of primates in the clade based groups of Strepsirhine and
Haplorhine.
Frenulem present
Postorbital bar
Long muzzle
Strepsirhine
Rhinarium present
Two part mandible
No rhinarium
No frenulem
Fused mandible
Haplorhine
Complete bony eye socket
Reduced muzzle
The Haplorhine category can further be divided into these two infraorders:
Platyrrhine (New World Monkeys)
Widely spaced, round nostrils
Catarrhine (Old World Monkeys)
Closely spaced, downward pointing nostrils
12 premolars
All have tails, some prehensile
Non-bilophodont molars
8 premolars
Not all have tails, none prehensile
Bilophodont molars