318 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lie 



south and west (Hunt, 1956, pp. 73-86), The ranges of certain 

 widespread species undoubtedly were fragmented first by these 

 upheavals and by the climatic changes that followed. 



Dry, warm, middle Pliocene climates produced grassland and 

 subdesert environments of great extent (Axelrod, 1948). Present 

 regional adaptations such as time of egg-laying may have originated 

 then in response to increasing aridity. It is probable that ensuing 

 dry conditions permitted northward dispersal of amphibians and 

 reptUes adapted to vegetative environments of the expanding Madro- 

 Tertiary Geoflora and that montane species associated with forests 

 of the Arcto-Tertiary Geoflora simultaneously were limited. Axelrod 

 (1950, 1958) and Darrow (1961) have reviewed the history of these 

 major geo floras. 



Many neontologists, including myself, believe that present plant 

 and animal distributions were slightly to highly modified by violent 

 climatic fluctuations during the Pleistocene. Considerable modifica- 

 tion of the extent of plant communities characterized this epoch. 

 Evidence presented by Antevs (1954), Clisby and Sears (1956), 

 Leopold (1951a), Murray (1957), and Wendorf (1961) in New Mexico 

 suggests that grassland and desert species withdrew southward at 

 or about the time of glacial advance and that woodland forms then 

 dispersed across former semiarid zones. 



Periglacial deposits are extensive on Mt. Taylor (Hunt, 1956, p. 

 38) , indicating that the Zuni region was not excluded from Pleistocene 

 climatic change. Glacial deposits have been recognized along the 

 north, east, and south sides of the Colorado Plateau; these extend 

 down to 7000 or 8000 feet in some areas (Hunt, 1956, p. 35). Martin, 

 Sabels, and Shutler (1961, p. 115) postulated that during a cool- 

 moist interval the pinyon-juniper savanna was displaced downward 

 1700 feet in the Grand Canyon, Arizona, or, in terms of life zones, 

 was 2000-4000 feet below its present lower limits. If Zuni life belts 

 were uniformly lower by 4000 feet at such a time, as Antevs (1954) has 

 estimated for lowered life zones at Santa Fe, then the present Plains 

 Life Belt with its characteristic species did not exist. 



Zuni life belts probably fluctuated in a manner similar to those 

 diagramed by Martin (1961, fig. 2) ; thus, plains species like Scaphiopus 

 bombifrons and Holbrookia maculata were absent when cool-moist 

 conditions favored heavy forests or open woodland at low elevations 

 but may have been present prior to such forestation. Coincidently, 

 woodland-canyon species such as Hyla arenicolor or Eumeces multi- 

 virgatus were provided new pathways for dispersal. The opposite 

 situation existed during warm-dry intervals; hence, woodland forms 

 have had the most limited gene flow in Hypsithermal time and 

 presumably within the past century. While such "alternating 



