1986] Porter — Sonoran genus Compsocryptus 15 
of the Tertiary somewhere in southwestern North America. Cer- 
tainly, its xerophilous species would have adapted well to the 
increasingly drier climates of post-Oligocene times and to the 
microphyll and sclerophyll Madro-Tertiary Geoflora which then 
overspread the ever-rising Sierra Madre and Rocky Mountains. On 
the other hand, Compsocryptus may have originated in western and 
southern South America, where so many of its relatives are centered 
today. Here, the Miocene climate paralleled that of the Sonoran 
region. By the end of the Miocene the Argentine pampas had 
become well developed, composites and other dry-adapted plants of 
open habitats were radiating vigorously, and long dry seasons began 
to characterize the middle latitudes as a result of the reduced rainfall 
and “the ever-increasing rain-shadow effect of the rising Andes” 
(Solbrig 1976:22-3). Thus arose the Chaco, an austral Sonora. 
Whatever may have been its genesis, Compsocryptus today is 
centered in the western United States and northern Mexico (15 
species). It also has 3 remarkable disjuncts: C. fasciipennis in tropi- 
cal Florida and Cuba, C. fuscofasciatus in the Peruvian Coastal 
Desert, and C. melanostigma in north Argentina and nearby areas 
in Paraguay and Brazil. 
Even the most geographically remote species of Compsocryptus 
differ only in apparently minor features of color and sculpture. This 
fact may suggest that the disjunctions noted above arose in compar- 
atively recent times. Both the increasing aridity of the later Tertiary 
and xerothermic episodes within the Pleistocene probably allowed 
semiarid communities (Thorn Scrub, Subtropical Deciduous Forest, 
etc.) to range almost uninterruptedly from the southeastern United 
States to Argentina. Wet periods during the Pleistocene (glacial 
maxima at higher latitudes) would have favored the expansion of 
forests and probably caused the fragmented distribution that is 
observed among modern Compsocryptus species. 
For example, “during a past period of low rainfall a prairie type 
flora, such as is found today in Texas and Arizona, was able to 
extend its range into the eastern United States, and remnants of this 
flora reflecting dry conditions still exist on parts of the west coast of 
Florida and on Big Pine Key” and other lower Florida Keys 
(Spencer and Stegmaier 1973:13). Such dry periods occurred both in 
the Pleistocene and in the climatically unsettled late Tertiary. They 
