Carleton and Musser (2005) redefined rodent suborders on the basis of a host of both morphological and molecular reasons. They defined the Sciuromorpha as including three families, Sciuridae, Aplodontiidae, and Gliridae. Of these, only the Sciuridae are truly sciuromorphous. The Aplodontiidae are protrogomorphous and the Gliridae are myomorphous. The connection between Aplodontiidae and Sciuridae has been proposed numerous times in the past. The two families have been united into a common infraorder (Sciurida) or superfamily (Sciuroidea). It has long been suggested that dormice (Gliridae) are not particularly related to the Myomorpha, and their zygomasseteric structure has been termed "pseudomyomorphy". The connection between squirrels and dormice has been almost exclusively suggested through genetic studies, and to a lesser degree via the fossil rodent Reithroparamys.
Carleton, M. D. and G. G. Musser. 2005. Order Rodentia. pp745–752 in Mammal Species of the World A Taxonomic and Geographic Reference (D. E. Wilson and D. M. Reeder eds.). Baltimore, Johns Hopkins University Press.