Diversity and evolution of the molar radicular complex in murine rodents (Murinae, Rodentia)

ObjectiveThis study was designed to characterize the radicular pattern diversity and evolution of murine molars. It aimed at identifying new morphological characters in order to improve our understanding of rodent diversity and systematics.MethodsA non-invasive technique was applied to extant and extinct murine species. For each molar, a virtual slice was computed from X-ray microtomographic data to visualize root number and arrangement. A geometric morphometric study was then conducted on first upper molars on a sample of 40 specimens, representing 10 species of the tribe Arvicanthini.ResultsThe radicular pattern enabled to retrieve phylogenetic murine groups settled by molecular data. Apodemus species, Malacomys longipes, Mus musculus, and species of the Praomys group all displayed a primitive pattern which consisted in two roots in each of their lower molars. Phloeomys cumingi and Batomys granti displayed singular root arrangements derived from this primitive pattern. Arvicanthini were distinguishable from all other African murines by their high root number. In addition, Procrustes analysis on first upper molars clustered specimens according to their genera.ConclusionsAn evolutionary trend toward increasing the molar root number is shown in many murine groups. The increased complexity of root pattern occurs by a progressive splitting of the primitive pattern. The fossil record shows that the increase in the root number within Arvicanthini was initiated at least 7 Myr ago. Root number and root positioning are demonstrated to be characteristics equivalent to those of the crown in murine rodent evolutionary studies.