522 TRACE FOSSILS Figure Key concepts in the study of trace fossils (A) Preservational variants of the same ichnotaxon, reflecting emplacement in sediments of different consistency (B) Different views of the same ichnotaxon reflect slight differences in the level of burrowing relative to the clay sand interface From Ekdale AA, Bromley RG, and Pemberton SG (1984) Ichnology The Use of Trace Fossils in Sedimentology and Stratigraphy SEPM Short Course No 15 Tulsa, OK: Society of Economic Paleontologists and Mineralogists (C) A slight angular difference between the plane of bedding/weathering and that containing the trace fossil results in different two dimensional views of the trace fossil (1 3) Scale bars, mm Figure Key concepts in the study of trace fossils (A) Open J shaped dwelling burrow and excavated pelleted sand (1), trackway (2), feeding structure (3), and faecal pellets (4) produced by the fiddler crab, Uca (B) Plan view of open burrow network produced by a crab, lobster, and fish (C) Examples of Rusophycus produced by a polychaete, snail, trilobite, and notostracan From Ekdale AA, Bromley RG, and Pemberton SG (1984) Ichnology The Use of Trace Fossils in Sedimentology and Stratigraphy SEPM Short Course No 15 Tulsa, OK: Society of Economic Paleontologists and Mineralogists resolution of phylum or class) by the morphology and inferred function of the trace fossil (e.g., ‘arthropod-produced trackway’) The body fossil content of the same, or surrounding, lithologies may be suggestive; for example, the breadth of a trackway may correspond to that of one, but not other, potential candidates The potential producers of trace fossils, however, include organisms with minimal preservation potential Furthermore, the same trace fossil may be produced by a variety of animals, precluding extrapolation of the producer’s identity between case studies The resting trace Rusophycus, examples of which in Palaeozoic marine sediments are often attributed to trilobites (see Fossil Invertebrates: Trilobites), also occurs in Mesozoic strata (after trilobites became extinct) and in sediments from (non-marine) environments that were never colonized by trilobites (Figure 4C)