Chapter 11 Evolution of Trace Fossil Communities

Abstract

This chapter discusses evolution of trace fossil communities. Paleontological community studies suffer from the inadequacies of the fossil record: (a) the ratio of fossilizable shell bearers to soft-bodied animals is variable and decreases with depth, (b) fossil assemblages represent time intervals of unknown duration, (c) post-mortem transport of skeletal remains has often admixed elements from alien habitats, and (d) digenetic solution tends to selectively eliminate parts of the original shell assemblages. These biases are considerably reduced in the truce fossil record, which includes the products of soft-bodied as well as shell-bearing organisms, is less affected by digenesis and not affected at all by sedimentary displacement. The structure and diversity of soft-bottom communities, as expressed in the trace-fossil record, is suggested to have evolved in the following successive phases. (1) pioneer phase with emphasis on trophic flexibility and large body size, (2) saturation phase with emphasis on trophic diversification, behavioral optimization and body size diminution to accommodate more species and increase their evenness within the limits of a given and predictable food resource, and (3) co-evolution phase with emphasis on the behavioral diversification of tropically equivalent species.