Incisor enamel microstructure analysis does not support a rodent suborder Sciuravida (most recent common ancestor of Ivanantoniidae, Sciuravidae, Chapattimyidae, Cylindrodontidae, Ctenodactylidae and all its descendants) as proposed by McKenna and Bell (1997). Early to middle Eocene Ivanantonia, Sciuravidae, and Prolapsus have the plesiomorphic rodent schmelzmuster with pauciserial Hunter-Schreger bands (HSB). Within the Cylindrodontidae a schmelzmuster with uniserial HSB evolved: early Eocene Dawsonomys and middle Eocene Jaywilsonomyinae possess a schmelzmuster with pauciserial HSB, and middle to late Eocene Cylindrodontinae have more derived schmelzmuster with uniserial HSB. Chapattimyidae and Ctenodactylidae represent a clade with the potential to evolve multiserial schmelzmuster. Early Eocene Chapattimyinae, Yuomyinae, and Cocomyinae have plesiomorphic schmelzmuster with pauciserial HSB, whereas middle Eocene Cocomyinae, Yuomyinae, late Eocene Protophiomys, early Miocene Baluchimyinae, and the Ctenodactylidae possess derived schmelzmuster with multiserial HSB. Uniserial and multiserial HSB are derived but represent different pathways of evolution. Schmelzmuster distribution supports the hypothesis of a basal dichotomy of Rodentia suggested by Luckett and Hartenberger (1985) characterized by an ischyromyoid clade with the potential to evolve schmelzmuster with uniserial HSB and a ctenodactyloid plus hystricognath clade with the potential to evolve schmelzmuster with multiserial HSB.