Abstract
This paper clarifies the identification of the three species referred by Tobien (1954) to the genus Masillamys from Messel, and more specifically provides a revision of their diagnosis and differential dental features, using an updated terminology. Based on specimens better preserved than the holotype (M. beegeri), it appears that this genus had an infraorbital area more hystricomorphous than sciuromorphous. As the genus shares dental features – like a long oblique postprotocristid or the occurrence of a metalophid I on the lower molars, the relatively well-developed hypocone on the upper molars, as well ashystricomorphy –, notably with Hartenbergeromys and Pantrogna, Masillamys is here included among the basal Theridomorpha.