Cephalomyidae is an extinct family of caviomorph rodents from South America. The specific relationships of the family are uncertain, and affinities to both chinchilloid and cavioid rodents have been supported (McKenna and Bell, 1997; Vucetich et al., 1999; Kramarz, 2001, 2005). Most recently, Kramarz (2005) performed a phylogenetic analysis supporting a relationship to the Cavioidea, as represented by Eocardiidae. McKenna and Bell (1997) questioned the validity of the family, placing the cephalomyid genera then known in Dasyproctidae, but Kramarz (2001) subsequently reasserted the distinctiveness of cephalomyids.