Hystricomorpha

Hystricomorpha (from Ancient Greek ὕστριξ, (hústrix), meaning "porcupine", and μορφή (morphḗ), meaning "form") is a term referring to families and orders of rodents which has had many definitions throughout its history. In the broadest sense, it refers to any rodent (except dipodoids) with a hystricomorphous zygomasseteric system. This includes the Hystricognathi, Ctenodactylidae, Anomaluridae, and Pedetidae. Molecular and morphological results suggest the inclusion of the Anomaluridae and Pedetidae in Hystricomorpha may be suspect. Based on , these two families are discussed here as represent

The Hystricognathi are an infraorder of rodents, distinguished from other rodents by the bone structure of their skulls. The masseter medialis (a jaw muscle) passes partially through a hole below each eye socket (called the infraorbital foramen) and connects to the bone on the opposite side. This, together with their lack of an infraorbital plate and the relative size of the infraorbital foramen, distinguishes hystricognaths from other rodent groups. The infraorder's name comes from Ancient Greek ὕστριξ (hústrix), meaning "porcupine", and γνάθος (gnáthos), meaning "jaw".

Ctenodactylomorphi is an infraorder of the rodent suborder Hystricomorpha that includes two living families, the Ctenodactylidae (gundis) and the Diatomyidae (Laotian rock rat).