In 1877, Marsh named two species of Nanosaurus in separate publications, based on partial remains from the Morrison Formation of Garden Park, Colorado.
Most recently, in 2007 Galton reevaluated Morrison Formation ornithischians and concluded that the femur on which "Nanosaurus" rex (and by extension Othnielia) is based is not diagnostic, and reassigned the BYU skeleton to Laosaurus consors, which is based on more diagnostic material.