Analysis of Morphological and Functional Characteristics of Mandible in the Sympatric Callosciurinae Squirrel Species Based on Geometric Morphometry

In order to reveal the morphological characteristics of the mandibles of sympatric coexisting close relatives and to explore the response of phenotype to sympatry, we studied the mandibles of 71 adult squirrels of four species from Guizhou Province of China were analysed by geometric morphometry. The results showed that there were significant differences in the size and shape of the mandibles of four closely related squirrels (Callosciurus erythraeus, Dremomys pyrrhomerus, Dremomys pernyi, Tamiops swinhoei). With respect to the size of the mandible, the species in descending order were C. erythraeus > D. pyrrhomerus > D. pernyi > T. swinhoei. The morphological variations in shape occurred mainly in the molar region, the angular and coronoid processes. We found that C. erythraeus had relatively wider angular and coronoid processes, a relatively wider and more robust masseteric fossa, and a greater mechanical advantage of the masseteric muscle. Two species of Dremomys squirrels have longer, flatter mandibles, which may facilitate faster masticatory rate. Although the mandible of T. swinhoei is the most slender in morphological, its overall structure exhibits a distinctly conical morphometric trajectory and has mechanical advantages similar to those possessed by D. pyrrhomerus.