?Oryzomys pliocaenicus is a fossil rodent from the Hemphillian (late Miocene) of Kansas, central United States. It is known from a single mandible (lower jaw) with the back part missing. All three molars are present, but very worn. Together, the molars are 3.6 mm long. The fossil was discovered in 1935 and described in 1939 as a possible species of Oryzomys (in open nomenclature). Later authors doubted this allocation and suggested that it may instead belong in Bensonomys or Jacobsomys, but the material may not allow a definite identification.