New rodent assemblages from the Eocene Dur At-Talah escarpment (Sahara of central Libya): systematic, biochronological, and palaeobiogeographical implications

Abstract

In this paper, we describe four fossil rodent taxa from two new localities situated in the Idam Unit ('Bioturbated Unit') of the Dur At-Talah escarpment in central Libya. These rodents belong to the family Phiomyidae (Hystricognathi) and are distributed amongst three genera (Phiomys, Protophiomys, and Talahphiomys gen. nov.) that include three new species (Phiomys hammudai sp. nov., Protophiomys durattalahensis sp. nov., and Talahphiomys libycus sp. nov.). Although some of these new species are morphologically close to certain phiomyids from the latest Eocene and Oligocene of the Jebel el-Qatrani Formation of the Fayum in Egypt, the Idam rodent faunas lack the abundant and somewhat morphologically derived Fayum phiomyids (such as: Metaphiomys, Gaudeamus, Paraphiomys, Phiocricetomys), thereby excluding a similar age for the Dur At-Talah rodent assemblages. More resemblance is shared with the phiomyid (Protophiomys algeriensis) of the Nementcha locality in Algeria, for which a late middle Eocene age is presently admitted. Protophiomys is a primitive representative of the phiomyid African radiation and it is represented at Dur At-Talah by a slightly more derived species (Pr. durattalahensis) than that of Nementcha, thereby suggesting a younger age for Dur At-Talah. As a result, the new rodent assemblages suggest a late middle Eocene age for the Idam ('Bioturbated') deposits of the Dur At-Talah escarpment. This age hypothesis is substantiated by other mammals (especially Proboscidea), which occur in the same sedimentological unit. Interestingly, the dental pattern of Protophiomys and that of Talahphiomys have