Four fossil rodent taxa are described from a new locality in the Oligocene Continental and Transitional Marine Deposits outcropping in the vicinity of Zallah, Sirt Basin, central Libya. These rodents belong to the infraorder Hystricognathi Tullberg, 1899, and are distributed amongst four genera (Metaphiomys Osborn, 1908; Phiocricetomys Wood, 1968; Talahphiomys Jaeger et al., 2010; and Neophiomys , new genus) that include one new species, Phiocricetomys atavus, and one new combination, Neophiomys paraphiomyoides (Wood, 1968), formerly Phiomys paraphiomyoides Wood, 1968. The specimens described here have profound implications for the phylogenetic and systematic status of early hystricognathous rodents and paleogeographical debates regarding their origin. Based on a cladistic analysis, Waslamys attiai Sallam et al, 2009, is transferred to the genus Protophiomys Jaeger et al., 1985, as Protophiomys attiai (Sallam et al, 2009), new combination. That species is the type species of the monobasic genus Waslamys Sallam et al., 2009, and the new combination places Waslamys Sallam et al., 2009, as a new synonym of Protophiomys Jaeger et al., 1985. The genus Protophiomys (including Waslamys) is classified in Protophiomyinae, new subfamily.
Some of the Libyan species reported here are morphologically close to hystricognathous rodent taxa described from the latest Eocene—early Oligocene Jebel Qatrani Formation of the Fayum in Egypt, suggesting a similar age for the Zallah rodent-bearing stratum. Correlation of the Zallah magnetic polarity stratigraphic section to the Geomagnetic Polarity Time Scale relies on biostratigraphic data. The preferred correlation with Chron C13 implies an earliest Oligocene age for the Zallah fauna. The Zallah assemblage of Oligocene hystricognathous rodents considerably improves our knowledge of the evolutionary history of African rodents. Likewise, positioning the Zallah fauna within a consistent chronological framework constitutes an important advance toward the goal of achieving a comprehensive network correlating Paleogene Afro-Arabian mammal localities.