S. George Pemberton

CHAPTER 4 – The Ichnofacies Paradigm: A Fifty-Year Retrospective

: The ichnofacies paradigm endures as the elegant, unifying framework within which accurate ichnological observations and reliable environmental interpretations can be derived from the rock record. These temporally and geographically recurring, strongly facies-controlled groupings of trace fossils reflect specific combinations of organism behavior (ethology), and constitute the benchmark animal-sediment responses to optimum environmental conditions. Seilacherian ichnofacies are distinctive, archetypal associations of traces. Ichnofacies are part of the total aspect of the rock, and consist of primary biogenic structures imparted by organisms responding in predictable ways to variations in energy conditions, deposition rates, food resource types, substrate consistency, water salinity, oxygenation, subaerial exposure, substrate moisture, and temperature, among others. Like lithofacies, ichnofacies are subject to Walthers Law, have lateral continuity, display predictable vertical successions, and lead to mappable constructs. Like all facies analyses, interpretations of ichnofaunas are improved substantially when evaluated in the context of the host rocks and their sedimentologic and stratigraphic implications.

Uses of Trace Fossils in Genetic Stratigraphy

SUMMARY: Trace fossils represent both sedimentological and paleontological entities and as such, constitute a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition and genetic interpretation of various discontinuity types. Ichnology may be employed to resolve surfaces of stratigraphic significance in two main ways: (1) through the identification of discontinuities using omission suites, comprising substrate-controlled ichnofacies (i.e., firmground Glossifungites Ichnofacies, hardground Trypanites Ichnofacies, and woodground Teredolites Ichnofacies) or palimpsest softground suites; and (2) through careful analysis of vertical softground ichnologic successions (analogous to facies successions). Integrating data derived from omission suites with paleoecological data from vertically and laterally juxtaposed softground ichnological suites greatly enhances the recognition and interpretation of potentially significant stratigraphic surfaces.

The Antecedents of Invertebrate Ichnology in North America: The Canadian and Cincinnati Schools

SUMMARY: The development of ichnology in North America radiated from two independent centers: the Canadian School, consisting of professional geologists generally associated with the Geological Survey of Canada, and the Cincinnati School, consisting predominantly of amateur paleontologists. Both schools had considerable impact but worked somewhat in isolation from the active European ichnological centers in Germany, France, and England. North American researchers were quick to realize that many of the markings described as fucoids were not seaweeds, but were, in fact, produced by animals.

Edward Hitchcock and Roland Bird: Two Early Titans of Vertebrate Ichnology in North America

SUMMARY: Vertebrate ichnology in North America has a long and distinguished history, starting with the remarkable discoveries by Edward Hitchcock of dinosaur footprints and trackways from the Connecticut River Valley. Hitchcock assembled a unique collection that is currently housed in the Pratt Museum, Amherst College, and his work essentially constituted the beginnings of ichnology as a viable sub-discipline of paleontology. Although his original interpretation that these Late Triassic repichnia were bird tracks was incorrect, he indirectly linked birds and dinosaurs. In the southwest, the gifted American Museum of Natural History collector Roland T. Bird discovered the first sauropod tracks from Cretaceous strata near Glen Rose, Texas. These tracks gave paleontologists a means of assessing the behavior of sauropods, compared to the inaccuracies of preconceived popular conception, and fledgling skeletal reconstructions. The observations of trackways, recording the activity of the organisms while they were alive, ultimately led to the recognition that sauropods actually walked on land and could support their weight rather than requiring water to buoy them, possessed an upright posture with limbs directly beneath them, held their tails above the ground rather than dragging them, and that some forms had adopted herd behavior.