Browsing by Subject "bears"

Mammalian dentitions exhibit extraordinary diversity in morphology and function. Yet,the mechanisms governing dental development are considered highly conserved across Mammalia. The inhibitory cascade (IC) model is a developmental model explaining variation in molar size proportions observed in mammals. The IC model predicts a range of dental phenotypes based on a dynamic of cumulative inhibition and activation in the sequential development of molars. Whereas most mammals fit these predictions well, bears(Ursidae) are a known exception.Here I employ dental topographic analysis to examine the developmental basis of ursine molar dentitions defying the IC model.I quantified two aspects of tooth shape:molar complexity using orientation patch count (OPC), and tooth size as the area of occlusal surface. As the complexity and size of a tooth mainly emerge based on two different developmental processes –patterning and growth, respectively –these measurements were used to decompose the two phases of tooth development producing the final phenotype. To this end, also an estimate of feature density was calculated.As in previous studies, the molar size proportions of bears were highly incongruent with the IC model. However, complexity along the molar row followed a trend more closely matching the model. Feature density was highest in the third molar. Altogether, these observations suggest an early arrest in the growth of the third molar as the principal cause for bears falling outside the predictions of the IC model –consequently supporting the idea of the inhibitory cascade as a plesiomorphy of Mammalia.As an auxiliary part of this project, I assessed the functionality of Morphoviewer, a new piece of software for measuring complexity. Morphoviewer was successfully applied to infer diet from tooth complexity in a limited sample of carnivorans; and was thus used for all further OPC analyses.