MOLECULAR AND PALEONTOLOGICAL ASPECTS OF THE TEMPO AND MODE OF EVOLUTION IN OTOMYS (OTOMYINAE, MURIDAE, MAMMALIA)

Molecular investigations, using single-copy DNA/DNA hybridization, were carried out to establish the relationships of Otomys, an African murid rodent representing the taxon Otomyinae. When compared to a large array of murine, gerbilline, and cricetomyine genera of the family Muridae sensu lato, Otomys appeared to be closely related to the African Murinae Arvicanthis and Oenomys, and these three taxa clustered, in order of decreasing relatedness, with Mus, Rattus, and Acomys. However, the morphological systematics suggested that the Otomyinae was a monophyletic subfamily of the Muridae sensu lato, not directly related to the Murinae. Indeed, members of the Otomyinae are characterized by a very peculiar dental pattern, not found in any other living subfamily of the Muridae. Paleontological data pertaining to the history of Otomyinae indicate that the typical dental pattern of a modern Otomys has been found at ca 3.7 million years (Makapansgat, South Africa), whereas an interesting fossil, Euryotomys, shows the beginning of the transition from the murine to the otomyine tooth pattern at ca 6.0-4.5 million years (Langebaanweg, South Africa). This paper presents an evolutionary hypothesis, using a molecular time scale and the results of a molecular phylogeny, for under-standing the relationships between the fossil taxa and the living Otomyinae and Murinae.