Castorimorpha is the suborder of rodents containing the beavers and the kangaroo rats. A 2017 study using retroposon markers indicated that they are most closely related to the Anomaluromorpha (the scaly-tailed squirrels and the springhare) and Myomorpha (mouse-like rodents).[1]
Carleton, M. D. and G. G. Musser. 2005. Order Rodentia. Pp 745–752 in Mammal Species of the World A Taxonomic and Geographic Reference. Johns Hopkins University Press, Baltimore.
McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN0-231-11013-8