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Towards a Renaissance in Tetrapod Ichnology: Florence 2004

This volume developed around many of the contributions made by the participants (Fig. 1) in the Terrestrial Tetrapod Ichnofacies and Ichnotaxonomy special symposium held at the 32nd International Geological Congress, Florence, Italy, on August 23, 2004 (see review of the symposium by Lucas, 2005). The symposium and its poster session covered a broad spectrum of topics spanning much of the Phanerozoic (Devonian to Recent) and a wide variety of tetrapods (amphibians to hominids). This compilation highlights a significant polarity between studies that focus on very specific ichnotaxonomic problems that are of primary interest to specialists, and very broad issues that pertain to the philosophical underpinnings of global scale ichnofacies definitions and implications. These areas of investigation, while touched on in the symposium and informal discussion, are explored in much greater detail in the present volume. Indeed, the editors asked authors to address the symposium theme wherever possible. One could argue that detailed ichnotaxonomy is a prerequisite for the introduction of general ichnofacies terminology. Thus, it might be considered logical to present the contributions in order of increasing generality, beginning with detailed ichnotaxonomy and culminated by the global ichnofacies discussion. However, this is the reverse of the organization ordained by the symposium title. Thus, we prefer to have an overview of the wood before we get too distracted by the individual trees. Our overview is initiated by Spencer Lucas, who reviews the entire Phanerozoic record of tetrapod footprints under the title of Tetrapod Footprint Biostratigraphy and Biochronology. His conclusions are that tetrapod track biochrons (time intervals based on the duration of tetrapod ichnotaxa) have long temporal durations and are of continental if not global spatial extent, at least from the Early Jurassic onwards, and so allow only a broad-scale palichnostratigraphy (sensu Haubold and Katsung, 1978). This may disappoint some specialists who have attempted fine scale palichostratigraphic zonations, but convincing evidence that such track-based resolution is robust, on either ichnotaxonomic or stratigraphic grounds, is generally lacking. So, the conclusions may be somewhat noncontroversial given the present state of knowledge, and the trend away from oversplit ichnotaxonomies. Thus, we can only speculate on how these tetrapod track biochrons, the first proposed for the entire tetrapod track record (Devonian–Neogene) may be refined in the future. We also contend that this symposium (like Ichnia 2004) was a stimulus to global thinking on these subjects, so we present the more general and provocative papers first in order to provide context for the more specific contributions that follow. In doing this we quickly discovered that there are at least two contrasting ichnofacies philosophies that in large measure draw their different tenets from the different traditions and conventions employed in vertebrate and invertebrate ichnology. These contrasting views are expressed in papers by Lockley on the one hand, and Hunt and Lucas on the other. From the early days of tetrapod ichnofacies study (Lockley et al., 1994) until recently (Hunt and Lucas, 2005), essentially similar tetrapod ichnofacies definitions have been employed: this is the original or “old paradigm.” However, in this volume Hunt and Lucas have explored the perhaps provocative “new paradigm” idea that existing tetrapod ichnofacies can be pooled into a small number of archetypal vertebrate ichnofacies that mirror terrestrial invertebrate ichnofacies. This view, according to Lockley (this volume), masks the fact that tetrapod ichnofacies are inherently more differentiated than invertebrate ichnofacies, and that the history of trace fossil research is more “a tale of two ichnologies” than an integration of two closely related subdisciplines. On the other hand, the establishment of a finite number of tetrapod ichnofacies may, as it did in invertebrate ichnology, stimulate a wider use and testing of ichnofacies concepts than is occurring at present. We stress that neither the old or new paradigms are sufficiently well-established to have attracted widespread acceptance and that each likely has its inherent strengths and weaknesses, both in theory and in practice. It is, however, useful to step back for an objective overview and realize that one model (the new paradigm) seeks to standardize all ichnology according to the traditions of invertebrate ichnology, whereas the other (the old paradigm) stresses inherent differences in the nature of invertebrate and vertebrates and the ichnologies they produce.