The Skull of Stephanomys and a Review of Malpaisomys Relationships (Rodentia: Muridae): Taxonomic Incongruente in Murids

Abstract

The cranial morphology of the extinct murid genus Stephanomys, previously known only by dental remains, is described here on the basis of partial skulls of three species of Pliocene age. Important cranial charactets of the genus ate a robust rostmm, a high zygoma, a wide zygomatic arch, a narrow interorbit, a large orbit, and an optic foramen in the backward position. In addition to some dental characters, Stephanomys shares most of these cranial traits with the extinct Malpaisomys from the Canary Islands. Some of these traits may be linked to the development of large eyes and life in a rocky environment. The peculiar dental pattem of Stephanomys (stephanodonty) is also present in some recent murids (Oenomys and Thamnomys) having a different skull morphology. A comparison with nine other extant genera of murids verified the relationship among Malpaisomys, Stephanomys, and Acomys, supporting our pmvious conclusion. Phenetic and cladistic analyses of 17 cranial and 23 dental characters show that skull morphology is phylogenetically informative but highly convergent and incongtuent with other partial evidente based on dental and biochemical characters. The combined analyses of skull and teeth illustrate a case of mosaic evolution in murids.