A new subfamily of geomyoid rodents (Mammalia) and a possible origin of Geomyidae

Two new species, Mojavemys galushai and Phelosaccomys neomexicanus are desc ribed from the Barstovian of New Mexico. Both of these species are assigned to a new subfamily, the Mojavemyinae. It is uncertain as to whether this n ew subfamily should be referred to the Heteromyidae or Geomyidae. Both Mojavemys an Phelosaccomys retain some heteromyid characteristics whil e developing advanced traits of geomyids. It is possible that these genera represent transitional forms between a heteromyid ancestor and advanced geo myines, thus deriving the Geomyidae directly from the Heteromyidae sometime in the middle Tertiary. It is also possible that the Mojavemyinae are a su bfamily of heteromyids only convergent with geomyids. A third possibility i s that the mojavemyines are among a group of middle Tertiary geomyoids from which both Recent heteromyids and geomyids were derived.