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Size Variability of the Teeth in Living Mammals and the Diagnosis of Closely Related Sympatric Fossil Species

Philip D. Gingerich
Journal of Paleontology
Vol. 48, No. 5 (Sep., 1974), pp. 895-903
Stable URL: http://www.jstor.org/stable/1303289
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Size Variability of the Teeth in Living Mammals and the Diagnosis of Closely Related Sympatric Fossil Species
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Abstract

The dentitions of sympatric fossil (or living) mammalian species which share a relatively recent common ancestor often cannot be distinguished by form alone. In such cases, size differences are important in diagnosing the species. Measurements of the length and width of the lower molars and premolars of large samples of 19 species of living mammals demonstrate that M1 is usually the least variable in size, and that P3, P4, and M3 are the most variable. The low variability of M1 is presumably related to the fact that it is the first permanent tooth to form and erupt, and to its central position in the tooth row. Because of its low variability, M1 is the best tooth on which to base size diagnoses of very closely related sympatric fossil species. Examples are given of the diagnosis of two species of the fossil primates Plesiadapis (at Cernay), Pelycodus (at Avenay), and Protoadapis (at Grauves). The ability to distinguish closely related sympatric species is fundamental to reconstructing the phylogenetic history of any group from the fossil record.

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