AMERICAN BATS — HANDLEY 215 



be accepted, then the morphological sunilarities between Old and New- 

 World Plecotus must be characters that were shared before dispersal 

 occurred. 



The primitive Corynorhinus-like Plecotus crassidens may have 

 reached Eurasia in a secondary Pliocene invasion, bringing it into 

 contact with the already widespread and firmly established P. auritus. 

 Apparently it did not persist beyond the early Pleistocene and left 

 no derivatives. 



Subgenus Corynorhinus 



The group of species that form the American subgenus Corynorhinus 

 seem to represent the stem of the evolutionary line that has developed 

 Barhastella, Euderma, and Plecotus. The present center of differentia- 

 tion of this division appears to be in the arid southwestern portion of 

 the United States. This area is presently inhabited by Plecotus town- 

 sendii, a form that is actively differentiating today. It is the most 

 abundant and widespread member of the subgenus, there is much 

 regional variation within its large geographic range, and its range is 

 fringed with derivatives from it or from its inmiediate ancestors. 



The evolution and present distribution of the Recent species of the 

 subgenus Corynorhinus can possibly be related to glacial disturbances 

 during the Pleistocene (fig. 26) . The picture presented in this figure 

 reduces the problem to its barest essentials and is almost certainly 

 oversimplified. Forms that occurred earlier in the Pleistocene 

 (Nebraskan, Aftonian, and Kansan ages) cannot be accounted for, 

 and it is very likely that other, now extinct, species existed within 

 the time represented in this diagram. For example, Plecotus tetra- 

 lophodon lived perhaps as recently as late Wisconsin glacial age. It 

 was closely related to P. toumsendii but probably was not ancestral 

 to it. P. alleganiensis probably lived as recently as the Sangamon 

 interglacial age. It was closely related to P. townsendii and P. 

 rafinesquii and may have been a direct ancestor of either of these 

 Recent species. 



The Pleistocene epoch was characterized by an alternation of 

 periods of warmth and cold. During the warm interglacial ages, 

 forms such as the species of Plecotus conceivably could have been 

 distributed across the continent from coast to coast, provided trees 

 or caves were present. During glacial times distribution patterns 

 were shifted southward, contracted, and may have been split into 

 isolated segments as icecaps moved southward toward the Gulf of 

 Mexico and through the Rocky Mountain range. The most southerly 

 advance of the ice brought it within 500 miles of the present Gulf 

 Coast. Adjacent to the ice front was a belt of treeless tundra of 

 unknown width. Faunas and floras were compressed southward 



