The grasscutter (Thryonomys swinderianus), variously known as the marsh cane-rat, ground hog and in francophone West Africa, the aulacode or incorrectly, the agouti is a rodent but not a rat proper, since it belongs to the Hystricomorpha (porcupine family). This rodent subclass embraces similar species in both the old and new world, species which were originally classified according to the differentiation of the masticatory musculature. Due to their spatial separation, a common origin has often been contested and the hystricomorphic rodents of the new world have now been classified as Caviomorpha (guinea pig relatives). Hystricomorpha are correctly comprised of hystricidae (family of porcupines), Bathyergidae (family of sand-diggers), Thryonomydae (family of grass-cutters) and Petromuridae (family of African rock-rats) with the Phiomydis (African tertiary) as the common tribe group. Grasscutters are found only in Africa, where they are represented by a single genus, Thryonomys (identical with Aulacodes). Most of the species, subspecies or breeds described can be allied to one of the two following groups of species: Thryonomys swinderianus the larger grasscutter and Thryonomys gregorianus, the lesser grasscutter.