Mandibular shape in the genus Marmota (Rodentia, Sciuridae): a preliminary analysis using outlines

Marmots are of prominent interest for sociobiologists studying mammal societies. They are also a fascinating group on which to test congruence between morphological information and molecular phylogeny and the possible occurrence of hemoplasy in the evolution of the sciurid skeleton. To investigate marmot morphological relationships, an analysis of the outlines of the posterior region of the marmot mandible was performed using Elliptic Fourier analysis. Outgroup species belonging to other sciurid genera were also included, and the efficacy of this technique to discriminate taxa based on the morphology of this mandibular region was assessed. The mandible outlines led to a partial separation of the groups under study, but the phylogenetic signal seems to be weak compared to previous studies of the marmot mandible. indeed, epigenetic influences acting on the posterior region of the mandible, an area of insertion of important masticatory muscles, may be a source of phenotypic variation that can mask the phylogenetic signal. However, interpretations must be made with caution as the posterior region of the mandible is an apparently suitable structure for outline analysis but the poor alignment of the outlines using standard elliptic Fourier methods made the study more complex than expected.