Masticatory muscle anatomy and functional performance of rodents and Djadochtatherioid multituberculates

Rodents exhibit conservative anatomy adapted for gnawing, which can be divided into four morphotype categories. This project quantifies and compares the mechanical advantage of a sample of rodents across the tree, evaluating the variation between the morphotypes during incisor and molar biting at a range of gape angles. Once the variation of rodents was established, this was compared and contrasted with that of three Cretaceous multituberculates, a fossil mammal group that has several similarities to modern rodents. Through 2D lever-arm mechanics and PCAs and MANOVAs of the data, the rodent morphotypes are compared with each other and with the multituberculate fossils. According to the results of this project, multituberculates are functionally distinct on homologous muscles but can individually be more similar to extant rodents than to each other, to a degree, and the morphotype categories within rodents are functionally distinct. The variation within each morphotype is broad, however, suggesting that assumptions should not be made about the mechanical efficiency and function of organisms based on their morphotype category without a more detailed exploration of their anatomical and functional characteristics. This project explores, supports and builds upon established interpretations of the functional difference between morphotypes and provides a stepping stone to future research on extant and fossil rodents and fossil multituberculates. Incorporation of multiple factors such as bite point and gape angle are critical to differentiating the categories, with the sample being more mechanically similar during gnawing and the extremes of high and low gape accounting for most of the variance in efficiency.