Morphological adaptation of the masticatory muscles and related apparatus in Asian and African Rhizomyinae species.

Abstract

The masticatory muscles and related apparatus of the hoary Rhizomys pruinosus and lesser bamboo rats Cannomys badius from Thailand, and the East African mole rat Tachyoryctes splendens from Ethiopia were morphologically examined and compared. The zygomatic arch was found to be robust in the two Asian species, with well-developed superficial, intermediate, lateral, and caudal parts of the deep layer of the masseter muscle. The temporal muscle was not well-developed in the hoary bamboo rat. The well-developed infraorbital foramen in the East African mole rat is consistent with the significant role of the medial part of the deep layer of the masseter muscle. These findings reveal that the Asian and African lineages are obviously different in terms of their masticatory systems, and indicate that the different taxa have evolved independently. These evolutionarily divergent taxa appear to represent examples of functional convergence in their similar adaptations to digging behavior and to a fossorial lifestyle.