The Pre-Pliocene Tennessee River and Its Bearing on 

 Crawfish Distribution (Decapoda: Cambaridae) 



J. F. Fitzpatrick, Jr. 



Department of Biological Sciences, 

 University of South Alabama, Mobile, Alabama 36688 



ABSTRACT.— Recent demand for fossil fuels has provided oppor- 

 tunities for extensive and detailed examination of surface and subsur- 

 face unfossiliferous clastic deposits of the Coastal Plain of the Gulf of 

 Mexico. Among the new discoveries is an ancient outlet directly into 

 the Gulf for the upper Tennessee River more than once during mid- 

 and late Tertiary times. Also discovered is evidence that the intrusion 

 of the Mississippi Embayment apparently occurred much later than 

 implied by surface outcrops in Mississippi and Alabama. Many Cam- 

 baridae distribution patterns show close associations with these Ter- 

 tiary deposits; included are Cambarellus , Fallicambarus, Faxonella, 

 Hobbseus, Procambarus (Acucauda), P. {Girardiella), P. (Leconticam- 

 barus), P. (Pennides), and P. (Scapulicambarus). Some possible inter- 

 pretations relating to these distributions are discussed, as is the pattern 

 of Orconectes and Cambarus invasion. Much detailed study is badly 

 needed, and potentially fruitful areas for investigation are indicated. 



The earliest attempts to explain the population of North America 

 by cambarid crawfishes were based on the assumption of a Mexican 

 epicenter, from which the major groups radiated to invade the United 

 States and Canada, east of the continental divide. This was probably 

 best articulated by Ortmann (1905). Subsequently, however, Hobbs has 

 presented a cogent and compelling series of arguments in favor of an 

 origin in the southeastern United States (1958, 1962a, 1967, 1969, 1981, 

 1984; Hobbs and Barr 1972). Probably his best statements appeared in 

 his treatment of the Pictus Group of Procambarus (1958) and his mas- 

 terly analysis of Cambarus (1969). He continued his strong contentions 

 in a monograph of Georgia species (1981) and an analysis of the distri- 

 bution of Procambarus (1984). 



Although a detailed analysis of phylogenetic relationships is inap- 

 propriate here, it does seem worthwhile to review some of the major 

 trends. Most of these are based on Hobbs. A ProcambarusAike ancestor 

 is generally accepted, and indeed no one has taken issue with Hobbs's 

 contention that the Pictus Group of the subgenus Ortmannicus, of all 

 extant species, is most like the ancestral form (1958). He has, however, 

 recently (1981, 1984) added that certain members of the subgenus Pen- 

 nides are among the most primitive. Although he has somewhat revised 

 his concepts of relationships (1972, 1981, 1984), Hobbs has retained 



Brimleyana No. 12:123-146, September 1986 123 



