Late Pleistocene and HoloceneMicrotus(Pitymys) (Rodentia: Cricetidae) in New Mexico

Abstract

Microtus (Pitymys) meadensis and M. (P.) quasiater show no special relationship to each other within the subgenus, and both differ greatly from M. (P.) ochrogaster. Samples of fossil Microtus (Pitymys) from late Pleistocene sites in southeastern New Mexico differ from each other and from modern M. ochrogaster to about the same degree as do some populations of modern M. ochrogaster from one another. All the southeastern New Mexican fossils pertain to that species as do mid-Holocene specimens from northwestern New Mexico and probably a late Pleistocene specimen from the southwestern part of the state. In southeastern New Mexico, M. ochrogaster was present near Dry Cave in small numbers during the mid-Wisconsinan, becoming and remaining more common until near the onset of full-glacial conditions, at which time they disappeared from the area. The region was repopulated in latest Wisconsinan times, but was again abandoned at the end of the Pleistocene. Tentative correlations between tooth characters and Pleistocene temperatures indicate that, in southeastern New Mexico, the mid-Wisconsinan was characterized by mild winters and hot summers; that following these conditions, severe winter temperatures and cooling summer conditions obtained, followed in turn by somewhat less cold winters and very cool summers. Absent during full-glacial times, the voles returned to severe winter temperature conditions and warming summers. In northwestern New Mexico, warmer summers and winters similar to or slightly cooler than at present obtained during the mid-Holocene.