Escape Burrowing of Modern Freshwater Bivalves as a Paradigm for Escape Behavior in the Devonian Bivalve Archanodon catskillensis

Abstract

Many freshwater bivalves restore themselves to the sediment water interface after burial by upward escape burrowing. We studied the escape burrowing capacity of two modern unionoids, Elliptio complanata and Pyganodon cataracta and the invasive freshwater venerid Corbicula fluminea, in a controlled laboratory setting varying sediment grain size and burial depth. We found that the relatively streamlined E. complanata is a better escape burrower than the more obese P. cataracta. E. complanata is more likely to escape burial in both fine and coarse sand, and at faster rates than P. cataracta. However, successful escape from 10 cm burial, especially in fine sand, is unlikely for both unionoids. The comparatively small and obese C. fluminea outperforms both unionoids in terms of escape probability and escape time, especially when body size is taken into consideration. C. fluminea can escape burial depths many times its own size, while the two unionoids rarely escape from burial equivalent to the length of their shells. E. complanata, and particularly P. cataracta, are morphological paradigms for the extinct Devonian unionoid bivalve Archanodon catskillensis, common in riverine facies of the Devonian Catskill Delta Complex of the eastern United States. Our observations suggest that the escape burrowing capability of A. catskillensis was no better than that of P. cataracta. Archanodon catskillensis was likely unable to escape burial of more than a few centimeters of anastrophically deposited sediment. The long (up to 1 meter), vertical burrows that are associated with A. catskillensis, and interpreted to be its escape burrows, represent a response to episodic, small-scale sedimentation events due to patterns of repetitive hydrologic or weather-related phenomena. They are not a response to a single anastrophic event involving the influx of massive volumes of sediment.