Dictionary of Human Evolution and Biology

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M1, M2, M3, Etc.

Notation that makes reference to molar teeth in which the most anterior tooth is the lowest number and the most posterior tooth is the highest number. The notation is either lower case (indicating a mandibular tooth; m1, m2, m3) or upper case (indicating a maxillary tooth; M1, M2, M3). There are two ways this system of numbering is used.

1. in reference to retention or absence of a tooth from the primitive eutherian set of teeth, the dental formula of which is: Molars may have been lost, in which case the existing teeth may have molars designated by a number larger than the actual number of teeth if the first molar has been lost; thus the molars would be designated as M2 and M3; the primate trend has been not to lose molars with the exception of the callitrichids (Family Callitrichidae), which have lost the third molar.

2. in reference to the teeth that are present in an existing species. The anterior molar is numbered M1, regardless of the ancestral condition.

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