A large-bodied anomaluroid rodent from the earliest late Eocene of Egypt: phylogenetic and biogeographic implications

Abstract

ABSTRACT A new genus and species of anomaluroid rodent, Kabirmys qarunensis, is described based on isolated teeth, partial mandibles, and an edentulous partial maxilla from the earliest late Eocene Birket Qarun Locality 2 (BQ-2) in the Fayum Depression of northern Egypt. Kabirmys is the largest known Paleogene anomaluroid, with first lower molar area being about 2.5 times that of the roughly contemporaneous Nementchamys and Pondaungimys from Algeria and Myanmar, respectively. The genus exhibits distinctive features not seen in other Paleogene taxa, such as a complete mure, weak neo-endoloph, and open lingual sinus on the upper molars; Kabirmys lacks the complex enamel crenulations seen in Nementchamys and Pondaungimys. Phylogenetic analysis of dental features nests Kabirmys within crown Anomaluridae as a sister taxon of Nementchamys and Pondaungimys, but parsimony analysis following addition of a chronobiogeographic character places all of these taxa as basal stem members of Anomaluridae. This new evidence indicates that there was considerable diversity in body size and molar morphology among African anomaluroids near the middle-late Eocene boundary, and suggests that the group had an ancient origin on that landmass. Kabirmys shares some primitive features with the possible zegdoumyid ‘Glibia’ namibiensis from the Paleogene of Namibia, and suggests that anomaluroids might be derived from a zegdoumyid-like ancestor. The disappearance of anomaluroids in the upper (latest Eocene to early Oligocene) levels of the Fayum succession might be related to global cooling through the later Paleogene, which might have removed suitable habitats from northern Africa.