Variation in the dentition of kangaroo rats (genus dipodomys) and its impligations for the fossil record

摘要

Recognition of paleospecies in the rodent family Heteromyidae relies heavily on quantitative dental characters because of a fragmentary record composed primarily of isolated teeth and a highly conservative dental morphology. However, no study has attempted to understand sources of variation in these quantitative characters to assess their reliability in making taxonomic decisions. Teeth of 17 species of the extant heteromyid genus Dipodomys, kangaroo rats, were measured and analyzed to determine these sources of variation. Analyses of covariance and multivariate analyses of covariance were performed to determine effects of sex and age on size of tooth. Age had a highly significant effect on size of tooth in all species, but effects of sex and a sex-age interaction were minimal. Dimensions of posterior teeth such as widths of upper and lower second and third molars were least affected by variation in age. Multiple-regression analyses indicated a significant portion of size of tooth variability in >33% of species could be accounted for by changes in latitude and longitude. This geographic variation had the most affect on widths of upper and lower premolars. These results indicate the need to account for age and geographic variation before attempting to make taxonomic decisions in the Heteromyidae using quantitative dental characters.