Over the years, we've participated in several different workshops and short courses on trace fossils. So why this one? Our intention in bringing together these papers for the Trace Fossil Short Course is to give an overview of how trace fossils can be used in paleontology. Historically, trace fossil research has centered on paleoenvironmental and depositional reconstructions—areas where trace fossils have much to tell. Indeed, the use of trace fossils by sedimentologists has flourished and is experiencing another burst of activity through the use of ichnofabrics in sequence stratigraphic studies. But trace fossils have paleontological stories to tell as well. Their use in uncovering the first occurrences of life in different parts of the stratigraphic column is well documented (e.g., the classic example of trace fossils occurring before body fossils in Precambrian/Cambrian transitional strata) as is their use in detailing different morphological details of unpreserved taxa or body parts.

Ichnotaxonomy is a formal, hierarchical classification system for trace fossils (=ichnofossils, the fossilized results of behavior). It includes a binomial nomenclature similar to the zoological taxonomic hierarchy applied to organisms. A common observation from non-ichnologists is that a formal system of classification and nomenclature for footprints, burrows, and other holes in the ground seems a bit excessive. Surely a burrow by any other name is still a burrow? However, ichnology has a real need of formal classification and names. There is a great diversity of both trace fossils and of processes that affect their form. Understanding and making use of this diversity requires an effective and generally agreed upon means of classification and nomenclature. To show that this is the case, one must understand both the principles of classification and how they are applied to trace fossils.

The study of fossil footprints began soon after the birth of vertebrate paleontology. The Reverend Henry Duncan started a study of footprints from the New Red Sandstone (Permian) of Scotland in 1824 (Sarjeant, 1987). Even earlier reports of footprints are known, but the fossils were not studied until later (Sarjeant, 1975). The first experiment in making trackways occurred around 1830, when the Reverend William Buckland walked a turtle across pie crust, wet sand, and soft clay. Chirotherium, one of the most famous ichnogenera, was described by J. F. Kaup in 1835. In 1836, Edward Hitchcock published the first of many papers describing dinosaur and other footprints from the Triassic and Jurassic of the Connecticut Valley (Sarjeant, 1987). The first Carboniferous footprints were discovered in 1841 in Nova Scotia by William Logan, and provided the first evidence of terrestrial vertebrate life older than the New Red Sandstone (Sarjeant and Mossman, 1978). Tertiary footprints were described by Jules Desnoyers in 1859 (Sarjeant, 1987). Studies continued through the nineteenth and the first three decades of the twentieth centuries. Permian trackways from the Grand Canyon were found in 1915 and extensively described by Gilmore (Gilmore, 1926, 1927, 1928; Spamer, 1984). Soon after this, however, the study of vertebrate trace fossils fell into disrepute. In the last decade or two, a resurgence of interest has occurred, primarily spurred by an interest in using dinosaur footprints to learn more about these animals (Sarjeant, 1987).

The purpose of this chapter is to evoke new concepts, provide guidelines and new frontiers for future research, and demonstrate that invertebrate traces actually comprise the “backbone” of continental (as well as marine) ichnology. Invertebrate organisms that inhabit the continental, nonmarine realm include some of the most diverse and populous classes in the animal kingdom. For example, both the Insecta and Crustacea exhibit burrowing behaviors unique to subaqueous freshwater and subaerial systems. Because of the sheer biomass of burrowing pupae, larvae, juvenile, and adult stages of these organisms, invertebrates dependent on the position of the water table form the basis for ecological niche-partitioning of depositional systems within all of the continental realm. A distinction must be made here between continental and marine ichnocoenoses because they represent distinctly different styles of living. These in turn dictate different behavioral and genetic responses of the organisms that inhabit them. Burrow architectures that occur in both continental and marine ichnocoenoses can be differentiated by subtle differences in morphology that are due to convergence of the burrowing mechanisms of the respective organisms.

Tracemaking organisms are common and diverse components of the fauna and flora of tropical, shallow-marine and coastal carbonate environments. In the shallow subtidal zone, the burrowing activity of callianassid shrimp commonly is the dominant process in the modification of original depositional fabrics (Tudhope and Scoffin, 1984; Tedesco and Wanless, 1991). Both borers and burrowers have great potential to leave their mark in tropical carbonate sediments and rocks and to become part of the fossil record.

“Bioerosion” was coined by Neumann (1966) as an abbreviation of “biologic erosion”, and describes every form of biologic penetration into hard substrates, i.e., lithic (including skeletal) and woody. An extremely wide range of organisms causes bioerosion (see Bromley, 1970; Warme, 1970, 1975; Ekdale et al., 1984, p. 108–139). The work of these organisms produces trace fossils at all scales, from microscopic to gigantic. Minute scars etched by brachiopod pedicles have a paleoecologic story to tell; at another scale, cliff sapping by communities of boring bivalves and rasping limpets can cause major geographic changes. For example, the work of pholad bivalves played a leading role in the separation of England from the European continent; and had the great armada, sent against England by Philip II of Spain in 1588, not been annihilated by wood-boring shipworms (bivalves), the language of this short-course would have been Spanish.

In the mid-twentieth century much of the impetus for paleoecological research was from the need for the fossil record to provide paleoenvironmental information. At that time earth scientists trying to understand the environmental context in which sedimentary rocks were deposited began extensive utilization of fossil components and sedimentary structures to make their interpretations. Towards this end, paleontologists and biologists catalogued the environmental preferences and depth distributions of modern organisms, and these modern distributions have been utilized in paleoenvironmental reconstructions by means of taxonomic uniformitarianism. Physical sedimentary structures have also been studied extensively in modern environments and laboratory simulations so that their occurrence in rocks can provide detailed information on ancient environments.

Trace fossils, as everyone knows by now, provide us with direct information about fossil behavior, and they offer us a wide variety of mysteries to solve in the area of paleoethology (literally, “the study of ancient behavior”). Chief among these mysteries are “what?”, “who?”, “why?” and “where?”. What we especially want to know is what a given trace fossil looks like in three dimensions, what type of organism(s) created it, for what reason(s) they made it, and under what type of environmental conditions the trace was made.

The general theme of this chapter is the relationships between trace fossils and benthic oxygen availability in marine environments. Discussion is organized into three sections, which correspond to related yet distinct approaches to the analysis of ichnofossil/oxygen relationships.

An examination of any modern terrestrial ecosystem will reveal a vast array of arthropod (particularly insect) — plant interactions. It has been calculated that there are more than one million extant insect species, more than 400,000 plant species, and that the total number of their interactions exceeds their combined total. Studies of the co-evolution of insects and plants have indicated that the development of these interactions must have taken considerable time (Southwood, 1973, 1985; Strong et al., 1984). For example, the evolution of the angiosperms (flowering plants) and insects are seen to be closely interlinked (Friis et al., 1987).

Nobody knows exactly when and where Lady Ichnology was born; but everybody would agree that she is coming of age. There are unmistakable signs of this: social acceptance, for instance, or its own journal, and a progeny that can only be estimated from the yearly flow of publications and from a regular newsletter sent out in numbers that make book publishers greedy.