page_title: Cheek teeth
section_title: Evolution
hierarchical_section_title: Cheek teeth / Evolution
caption_attribution_description: English: Fig. 39.—Epitome of the evolution of a cusped tooth. 1, Reptile; 2, Dromatherium; 3, Microconodon; 4, Spalacotherium; me, metaconid; pa, paraconid; pr, protoconid; 5, Amphitherium. (After Osborn.)
context_page_description: Cheek teeth or post-canines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate. Mammals have multicuspidate molars and premolars situated between canines and molars whose shape and number varies considerably among particular groups. For example, many modern Carnivora possess carnassials, or secodont teeth. This scissorlike pairing of the last upper premolar and first lower molar is adapted for shearing meat. In contrast, the cheek teeth of deer and cattle are selenodont. Viewed from the side, these teeth have a series of triangular cusps or ridges, enabling the ruminants' sideways jaw motions to break down tough vegetable matter. Cheek teeth are sometimes separated from the incisors by a gap called a diastema.
  Cheek teeth in reptiles are much simpler as compared to mammals.
context_section_description: Mammalian, multicusped cheek teeth probably evolved from single-cusped teeth in reptilians, although the diversity of therapsid molar patterns and the complexity in the molars of the earliest mammals make determining how this happened impossible. According to the widely accepted "differentiation theory", additional cusps have arisen by budding or outgrowth from the crown, while the rivalling "concrescence theory" instead proposes that complex teeth evolved by the clustering of originally separate conical teeth.  Therian mammals (placentals and marsupials) are generally agreed to have evolved from an ancestor with tribosphenic cheek teeth, with three main cusps arranged in a triangle.
caption: Comparison of cheek teeth in various taxa: 1, reptile; 2, Dromatherium (a Triassic cynodont); 3, Microconodon (a Triassic eucynodont); 4, Spalacotherium (a Cretaceous symmetrodont); 5, Amphitherium (a Jurassic mammal)
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