Comparative taphonomy and palaeoecology of trilobite lagerstätten

Trilobite remains display a range of taphonomic properties which provide useful information regarding the distribution of environmental conditions. Particular deposits, when viewed in proper perspective, may represent specific palaeobiological and behavioural phenomena for which tenable explanations can be proposed and evaluated. Trilobite lagerstätten typically comprise thoroughly and partially disarticulated remains, and less frequently include outstretched and/or enrolled corpses and intact exuviae. Rarely, trilobite remains (carcass, moult, or disarticulated segments) compose dense, localized patches and bioclastic deposits. Taphonomic properties appear non-randomly in the stratigraphic record and, therefore, characterize taphonomic facies (or taphofacies). Comparative taphonomy of remains provides an index by which ambient sedimentary conditions can be characterized and palaeoenvironmental settings synthesized. Trilobites, like other organisms with multi-element skeletons, were particularly sensitive to disarticulation. In general, nearshore facies are characterized by an abundance of disarticulated remains. Biostratinomic details indicate that disarticulation was mediated by one or more of three processes: current agitation, shallow (surficial) bioturbation, deep (intrastratal) bioturbation. Offshore facies, in contrast, are distinguished by a greater number of articulated moults and bodies, sometimes associated with the by-products of early carbonate and/or pyrite diagenesis. The relative abundance of disarticulated tergites, outstretched carcasses, enrolled corpses, and intact exuviae provides important data that are related to specific physico-chemical phenomena associated with sedimentary events (e.g., storms, turbidity currents). As vagrant benthos, trilobites were characterized by complex behaviour which may be reflected by biostratinomic details of their articulated remains. Trilobites, like most arthropods, moulted and therefore contributed potentially fossilizable material to the sediment prior to death. Articulated remains provide the only tangible data available for understanding fossil trilobites as once living organisms with diagnostic biological and behavioural attributes. Detailed taphonomic comparisons call attention to otherwise unsuspected aspects of trilobite ecdysis, enrollment, and gregarious behaviour.