Aquatic Distributional Patterns in the Interior Low 



Plateau 



Branley Allan Branson 



Department of Biological Sciences, 

 Eastern Kentucky University, Richmond, Kentucky 40475 



ABSTRACT. — The aquatic gastropod and fish faunas of the Interior 

 Low Plateau of extreme southern Indiana, Illinois (Wabash River 

 drainage), Kentucky, Tennessee, and northern Alabama reflect the 

 interaction of tectonic changes, glaciation, eustatic stream modifica- 

 tions, piracy within the Low Plateau and in extralimital drainages 

 (particularly the Coosa-Alabama system), immigration from trans- 

 Mississippian systems, speciation within drainages that cross the Low 

 Plateau, and survivorship as relicts. Examples in the Pleuroceridae, 

 Unionidae, and several fish families are discussed, with emphasis on 

 percid darters and the catfish genus Noturus. 



INTRODUCTION 



The Interior Low Plateau of extreme southern Indiana, Illinois 

 (Wabash River drainage), Kentucky, Tennessee, and northern Alabama 

 (Fenneman 1938; Quarterman and Powell 1978) is a biological cross- 

 roads between regions that are faunistically and floristically rich. 

 Understanding of the biological importance of this unique region has 

 come very slowly, piecemeal really, mostly because of inadequate study 

 and failure in the synthesis of existing information. The present biota is 

 quite complex, consisting of mixtures of types from diverse centers of 

 origin, including a rather large number of relicts and endemics. To 

 extrapolate from knowledge of existing biotas back into the past in 

 order to understand the present is not a bad approach, particularly if 

 there are considerable supporting geologic and paleontologic data 

 available. 



MOLLUSCA 



In the discussion that follows, I have elected to retain Goodrich's 

 nomenclature (see literature cited) rather than the combinations recently 

 espoused by Burch (1982), since most readers are not familiar with the 

 resurrected combinations. Furthermore, there is still considerable dis- 

 agreement regarding some of the combinations. 



In the early part of this century, well-diggers near Henderson, Ken- 

 tucky, cut into a deposit 25.5 m below the surface. The strata were 

 determined to be of Yarmouthian Interglacial age (Baker 1920). The 

 mollusks removed from those deposits included specimens of Campe- 

 loma crassula Rafinesque, Pleurocera canaliculatum (Say), Planorbula 



Brimleyana No. 1 1 : 1 69- 1 89, October 1 985 1 69 



