Prehistoric Biogeography and Conservation Status of Threatened Freshwater Mussels (Mollusca:Unionidae) in the Upper Trinity River Drainage.

In Texas, fifteen freshwater mussel (Unionidae) species are listed as threatened, of which nine are being considered for protection under the Endangered Species Act (ESA). Two threatened species are thought to occur in the upper Trinity River drainage of north central Texas: Potamilus amphichaenus and Pleurobema riddellii. The magnitude of decline of these species is unknown given the dearth of historical surveys. Using zooarchaeological remains, we provide evidence suggesting that P. riddellii was more widely distributed during the late Holocene (600 to 2500 B.P.) than it is today. Potamilus amphchaenus is absent from archaeological sites in this drainage but this is likely due to underlying taphonomic factors related to preservation. In addition, we document Lampsilis satura, which is outside of its modern range. Comparisons between zooarchaeological and modern / historical records for P. riddellii and L. satura indicate these species are good candidates for protection under the ESA.