Steneofibers are among the earliest known members of the subfamily Castorinae, which includes beavers more closely related to the two living species than to the recently extinct giant beaver. It is probably directly descended from the earliest known castorine, Propalaeocastor.
Steneofibers belong to a group of early beavers called Castorinae, which are closer relatives to modern beavers than to the extinct giant beaver. They likely evolved from the first known member of this family, Propalaeocastor.