136 J. F. Fitzpatrick, Jr. 



less susceptible to weathering, were present in expected amounts. This, 

 plus other mineralogical considerations, led to an hypothesis that the 

 period was characterized by a warm, moist climate. A similar suite in 

 the comparable Pascagoula-Hattiesburg Formation indicates that this 

 area, too, was far from arid (Isphording 1983). Florida presents a 

 somewhat different and contradictory picture, but it is outside the con- 

 siderations of this paper; presumably Florida conditions influenced Alt's 

 thinking. The conclusions of Isphording, however, are compatible with 

 the position of Dorf (1960) who envisioned a subtropical or tropical 

 climate on the Gulf Coast throughout the Tertiary and during intergla- 

 cial stages of the Pleistocene. 



ZOOGEOGRAPHIC IMPLICATIONS 



Turning now to animal distribution, we find certain enigmatic fea- 

 tures. One of these is the Cambarellinae. Every evidence indicates an 

 early divergence from cambarine stock. Yet the more primitive members 

 of the genus are found associated with the marginal areas of the Gulf 

 Coastal Plain. Fitzpatrick (1983) noted that almost every site from 

 which the genus has been collected in Mississippi (and Florida/ Georgia) 

 is south and east of Brown's (1967) ridges or on the Mississippi River 

 flood plain (Fig. 7). Although not as pertinent to this discussion, a sim- 

 ilar restriction to geologically recent areas of the Coastal Plain in Loui- 

 siana and Texas exists, with deep inland areas being invaded only in 

 Mexico. 



Fitzpatrick (1983) believed the ancestral cambarellid was most like 

 Cambarellus puer Hobbs and its relatives; but among the species he 

 considered as candidates for this status, all are outside the site of origin 

 for the Cambaridae proposed by Hobbs. Quite clearly, the dwarf craw- 

 fishes arose from a stock that became established in the lower Missis- 

 sippi River lowlands shortly after the emergence of the subfamily and 

 before much diversification of populations began. A temporal assign- 

 ment of this event is difficult, but it could easily have occurred when 

 proposed by Hobbs (late Cretaceous or early Cenozoic). Their subse- 

 quent diversification and expansion east of the Mississippi River delta, 

 however, could not have occurred before Miocene times. If, as proposed 

 by Isphording and Flowers (1983), Brown's (1967) ridges represent a 

 reworking of Miocene deposits, rather than primary deposits, then the 

 eastward expansion is post-Miocene, probably late Pliocene. Further, 

 their distributions give a relatively clear indication that no easy access to 

 lentic habitats of the upper Coastal Plain existed. 



On the lower Gulf Coastal Plain, the temporary bodies of water are 

 dominated by Cambarellus, Faxonella, Procambarus (Capillicambarus), 

 P. (Scapulicambarus) clarkii, and the ubiquitous, probably multi-species 

 taxon, P. (Ortmannicus) acutus acutus. All are tertiary burrowers. They 

 are complemented, often sympatrically, by primary burrowers of Falli- 

 cambarus, Cambarus (Lacunicambarus), Procambarus (Acucauda), and 

 P. {Hagenides). The upper Coastal Plain and inland areas have an 



