Complex Trace Fossils

Complex trace fossils include large, elaborate structures that appear to indicate long occupation and control of environmental factors; structures referred to as compound ichnotaxa, which represent different kinds of functions or behaviors within the same complex system; and certain forms of composite trace fossils that record intimate, recurrent ecologic associations of two or more trace-producing organisms. Their functional interpretation can be approached by teasing out evidence of construction, operation and maintenance, and portraying the results in a stylized paleoethologic blueprint showing behavioral subroutines arranged in spatiotemporal order. Complex trace fossils do not represent a fleeting, superficial interaction with the surrounding environment, but instead appear to record sophisticated ecologic roles and interactions, ability of the producers to actively construct a special habitat for themselves, and in some cases special behavior involved in controlling food supplies or other essential life functions. From this point of view, some of these intricate structures could be considered as phenotypic extensions or physiologic projections of the trace producers—in other words, parts of the bodies of the organisms that built and utilized them.