Chapter 33 - Ecological and Evolutionary Controls on the Composition of Marine and Lake Ichnofacies

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The usefulness of trace fossils and patterns of bioturbation in interpreting ancient sedimentary has been well known, but their potential for answering paleobiological questions has not been fully explored. The use of trace fossils as environmental indicators is rooted in the concept that animals use optimal behaviors that are controlled by environmental and evolutionary parameters. Extensive study of modern benthic communities in the mid-twentieth century provided the uniformitarian basis for this ichnofacies paradigm. In the past thirty-five years, the paradigm has been modified and the level of resolution of trace-fossil based environmental interpretation has increased primarily through careful documentation of ichnofossils, ichnofabric, and ichnofacies in well-studied sedimentary sequences rather than by integration of information about modern animal–sediment relations. Application of marine-based ichnofacies paradigms to lake deposits is problematic because freshwater macrobenthos are dominated by relatively few infaunal groups whose body plans, evolutionary histories, and life cycles limit burrowing behavior to producing small, shallow, and simple traces. The ultimate causes of the comparatively taxonomically poor lake infauna and ichnofauna probably include the efficacy of the estuarine filter, the temporal and spatial variability of key lake environmental conditions, the geographic isolation of lakes, and the commonly short geological duration of individual lake ecosystems.