A NEW METHOD FOR MEASURING UNILATERALLY HYPSODONT TEETH WITH EXAMPLES FROM LAGOMORPHA AND RODENTIA

Most work on hypsodonty has focused on large mammalian herbivores (ungulates and functional equivalents) and on types of hypsodonty characterized by straight, prismatic or columnar teeth. Standard measurements of occlusal dimensions and hypsodonty indices comparable between taxa are easily derived for such teeth that approximate elongated cubes. However, this approach does not work well for more complex teeth of some mammal groups. One form of hypsodonty that apparently has occurred predominantly in smaller herbivores is partial or unilateral hypsodonty in which the enamel border is much closer to the occlusal surface on one side of the tooth than the other, easily visible when viewed from an anterior or posterior view. Some members of Lagomorpha and Rodentia have particularly complicated curved, unilaterally hypsodont teeth which have a prominent rotational component to ontogenetic replacement.

Several problems are associated with determining quantitative measurements for unilaterally hypsodont, curved teeth that have prevented their usefulness in systematic characterization. Perhaps the most important are: 1) wear is greater on one side of the tooth than the other, causing occlusal dimensions to change with wear; 2) occlusal patterns and dimensions may reflect a combination of wear and systematic differences; 3) there is no standard for quantitatively determining amount of wear, and qualitative wear stages are usually highly taxon-specific; 4) standard hypsodonty indices are not applicable because linear measurements on curved teeth will not be reflective of true crown height.

I have developed a method for obtaining common, systematically useful dental measurements, determining relative stage of wear and a quantitative assessment of ontogenetic age, and determining a "standard" hypsodonty index for some Miocene beavers (Rodentia, Castoridae) and pikas (Lagomorpha, Ochotonidae) that should be applicable to other taxa with curved, unilaterally hypsodont teeth.