Predators and predation in the Cambrian period : quantitative methods in taphonomy and paleoecology

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The onset of predation profoundly affected early metazoan communities, likely triggering new biological innovations, such as an evolutionary arms race of prey defenses and predatory attacks, ultimately culminating in the geologically drastic radiation of major phyletic stem groups during the "Cambrian Explosion". Predation is understood primarily from two different means of interpreting the fossil record: either inferred from functional morphologies of organisms and interpreted based on those specializations, or from rare instances where predatorprey interactions, or their traces, are directly preserved. We first taphonomically analyzed the different disarticulated anatomies of the Middle Cambrian predator, Anomalocaris using microchemical analyses. From these analyses the samples appear to be preserved through typical Burgess Shale-type carbonaceous compression, with possible preservational influence of both pyritization and aluminosilicification. In a second study, we examine direct evidence of predatory ichnofossils from recurring associations of the arthropod ichnogenera Rusophycus and Cruziana (most commonly attributed to trilobites) with burrows of vermiform animals, interpreted to represent direct feeding behavior of the arthropod tracemaker on the burrowing worm. Here, we examine the Upper Cambrian Davis Formation, near Leadwood, southeastern Missouri. From our investigation of this material, we observe both size selectivity and possibly orientation of attack of the predatory traces, indicating a likely predator-prey interaction