Rodent Suborders

For two hundred years the status of rodent suborders has been unstable. What are the natural groupings of extant rodent families? The formal recognition of rodent suborders has remained challenging and consensus has been elusive. Classically conceived rodent suborders are widely viewed as artificial, but no universally accepted classification has emerged to reflect the major features of rodent evolution. Over the last two decades molecular studies have established that extant rodents comprise three monophyletic clades. We review the molecular basis for these groups and recognize them as taxonomic units: Suborder Ctenohystrica Huchon et al., 2000, Suborder Supramyomorpha D’Elía et al., 2019, and a group of families clustered with Sciuridae. The latter differs from Sciuromorpha as traditionally conceived because the suborder includes Aplodontiidae but excludes Castoridae. We review morphological character complexes that are distributed broadly within these three clades, name the third group Eusciurida, new suborder, and find this three-fold division of extant Rodentia to reflect well the major features of rodent phylogeny. That some morphological features do not characterize all families within suborders, or are not unique to individual suborders, indicates major parallel innovations and reversals in rodent evolution. These incongruent morphologies invite future study.