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In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. [2] [3] Human dentition is heterodont and diphyodont as an example. [4] In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms.
Horse teeth can be used to estimate the animal's age. Between birth and five years, age can be closely estimated by observing the eruption pattern on milk teeth and then permanent teeth. By age five, all permanent teeth have usually erupted. The horse is then said to have a "full" mouth.
An animal's dentition for either deciduous or permanent teeth can thus be expressed as a dental formula, written in the form of a fraction, which can be written as I.C.P.M I.C.P.M, or I.C.P.M / I.C.P.M. [10] [11] For example, the following formulae show the deciduous and usual permanent dentition of all catarrhine primates, including humans:
Generally, tooth development in non-human mammals is similar to human tooth development. The variations usually lie in the morphology, number, development timeline, and types of teeth. [8] However, some mammals' teeth do develop differently than humans'. In mice, WNT signals are required for the initiation of tooth development.
The toothcomb of most lemuriforms includes six finely spaced teeth, four incisors and two canine teeth that are procumbent (tilt forward) in the front of the mouth. [4] [15] The procumbent lower canine teeth are the same shape as the incisors located between them, [15] but they are more robust and curve upward and inward, more so than the incisors. [13]
Tooth structures bear suffixes in order to note the type of structure they are and whether they are present in the upper or lower molars.. The suffix "-cones /-conids" (upper molar/lower molar) is added to the main cusps: Paracone, Metacone, Protocone and Hypocone on the upper molar, and Paraconid, Metaconid, Protoconid, Hypoconid and Entoconid on the lower molar.
Animals where this occurs include antelopes, musk-deer, camels, horses, wild boar, some apes, seals, narwhal, and walrus. [6] Male dogs have larger canines with different contour than do females. [7] Humans have the proportionately smallest male canine teeth among all anthropoids and exhibit relatively little sexual dimorphism in canine tooth size.
It was theorized that positive selection for shovel-shaped incisors over the spatulate incisors is more commonly found within cultures that used their teeth as tools due to a greater structural strength in increased shovel-shaped incisors. [2] In some instances, incisors can present a more pronounced version of this called double shovel-shaped.