Paleopathology of a mastodont molar.
This specimen (Fig. 1) consists of two, fused teeth. The primary (less deformed) tooth is a right M3; it has four transverse lophs, three roots, and is 130 mm long anteroposteriorly. It has ptychodont enamel, and its visible crown is nearly surrounded by a discontinuous basal cingulum. This primary tooth of USNM 2225 is unusually short for a M3 of Mammut americanum, which normally is about 160 to 225 mm long (Skeels, 1962; Lucas, 1987). However, it otherwise generally resembles a normal, 161-mm-long, right M3 of M. americanum from the same locality (compare Figs. 1A and 1B).
However, the secondary (supernumerary) tooth of USNM 2225, which is lingual to the primary tooth, is badly deformed. It has only three lophs, and they are pushed together anteroposteriorly. Only two roots are present. The enamel of the secondary tooth is ptychodont, and a basal cingulum can be seen on the lingual edge of the crown. A line of fusion between the crowns and the roots of the secondary and primary teeth is clear, and the crowns are united by enamel and the roots by dentine. Neither tooth is worn.
Using the terminology of Pindborg (1970:48-54), supernumerary and doubled (connate) teeth can be produced in four ways:
1) "Gemination" may produce a tooth with a bifid crown and a single pulp cavity. This is believed to result from the partial division of a single tooth bud.
2) "Twinning" (schizodontia) produces two teeth that are often mirror images of each other. This is thought to result from the complete cleavage of a single tooth bud.
3) "Fusion" (synodontia) produces teeth that are united by their dentine or enamel or both as the probable result of the union of two or more tooth buds.
4) "Concrescence" is the condition in which the roots of two or more teeth are united by cementum after the formation of their crowns. True concrescence occurs when this union is during tooth development and may result from a lack of space or dislocation of tooth germs. If the union occurs after root formation, it is referred to as acquired concrescence. Acquired concrescence usually results from chronic inflammation that leads to hypercementosis.
Inasmuch as the primary and secondary teeth of USNM 2225 are united by their enamel and dentine, they almost certainly represent the fusion of two tooth buds. It seems less likely that the secondary tooth is the result of gemination because it has distinct roots and a relatively distinct crown, indicating that it has its own pulp cavity. That the secondary tooth is not a mirror image of the primary tooth argues against twinning as a cause. And, concresence can be ruled out because the two teeth are not united by cementum.
Moodie (1923: pl. 45) illustrated USNM 2225 as "an anomalous mastodon molar." Although he did not explicitly explain the origin of the abnormality, he included the illustration in a chapter on dental caries in fossil teeth. However, USNM 2225 clearly is two teeth, a primary and a supernumerary tooth and the likely result of fusion (synodontia). This is the first case of a supernumerary tooth formed by fusion documented in an extinct proboscidean.
[FIGURE 1 OMITTED]
I thank R. J. Emry and R. Purdy for permission to study specimens in their care.
Hay, O. P. 1924. The Pleistocene of the middle region of North America and its vertebrated animals. Publ. Carnegie Inst. Washington, 322A:1-385.
Lucas, S. G. 1987. American mastodont from the Sandia Mountains, New Mexico. New Mexico J. Sci., 27:29-32.
Lucas, S. G., and R. M. Schoch. 1987. Paleopathology of early Cenozoic Coryphodon (Mammalia; Pantodonta). J. Vert. Paleo., 7:145-154.
Moodie, R. L. 1923. Paleopathology an introduction to the study of ancient evidences of disease. Univ. Illinois Press, Urbana, Illinois, 567 pp.
Pindborg, J. J. 1970. Pathology of the dental hard tissues. W. B. Saunders, Philadelphia, 443 pp.
Skeels, M. A. 1962. The mastodons and mammoths of Michigan. Papers Michigan Acad. Sci., 47:101-133.
SPENCER G. LUCAS
New Mexico Museum of Natural History, 1801 Mountain Road N.W., Albuquerque, New Mexico 87104
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|Title Annotation:||GENERAL NOTES|
|Author:||Lucas, Spencer G.|
|Publication:||The Texas Journal of Science|
|Date:||Aug 1, 1992|
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