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Mammal tooth
Teeth are common to most vertebrates, but mammalian teeth are distinctive in having a variety of shapes and functions. This feature first arose among the Therapsida (mammal-like reptiles) during the Permian, and has continued to the present day. All Therapsid groups with the exception of the mammals are now extinct, but each of these groups possessed different tooth patterns, which aids with the classification of fossils.
==Diversity==
The extant mammalian infraclasses each have a set dental formula; the Eutheria (placental mammals) commonly have three pairs of molars and four premolars per jaw, whereas the Metatheria (marsupials) generally have four pairs of molars and between three or two premolars. For example, the tiger quoll (''Dasyurus maculatus'') is a dasyurid marsupial native to Australia. The quoll possesses four upper incisors and three lower incisors per left and right-hand side (= 14 ). Along with two upper premolars () and two lower premolars per side (= 8 ) and four upper and four lower molars per side (= 16 ), giving the animal a complement of thirty-eight teeth.
The Tiger quoll's dental formula is as follows:
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