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Nonindependence of mammalian dental characters


Studies of mammalian evolution frequently use data derived from the dentition1,2,3,4. Dental characters are particularly central for inferring phylogenetic relationships of fossil taxa1,2,3,4, of which teeth are often the only recovered part. The use of different aspects of dental morphology as phylogenetic signals implies the independence of dental characters from each other. Here we report, however, that, at least developmentally, most dental characters may be nonindependent. We investigated how three different levels of the cell signalling protein ectodysplasin (Eda)5 changed dental characters in mouse. We found that with increasing expression levels of this one gene, the number of cusps increases, cusp shapes and positions change, longitudinal crests form, and number of teeth increases. The consistent modification of characters related to lateral placement of cusps can be traced to a small difference in the formation of an early signalling centre at the onset of tooth crown formation. Our results suggest that most aspects of tooth shape have the developmental potential for correlated changes during evolution which may, if not taken into account, obscure phylogenetic history.

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Figure 1: Mouse molar teeth differ in several characters in mice with no (Tabby), normal (wild type), and above normal (K14-Eda) ectodysplasin activity.
Figure 2: Dynamics of Shh expression in developing first molar (a) and extra tooth (b).


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We thank F. Ankel-Simons, M. Fortelius, J. Eronen, K. Kavanagh, S. King, J. Meng, P. Munne, T. Mustonen, J. Pispa, S. Pochron, I. Salazar-Ciudad, E. Seiffert, and P. C. Wright for comments or help on this work, which was supported by the Academy of Finland.

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Correspondence to Jukka Jernvall.

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Kangas, A., Evans, A., Thesleff, I. et al. Nonindependence of mammalian dental characters. Nature 432, 211–214 (2004).

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