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COLLECTING INVERTEBRATE TRACE FOSSILSby Stephen K. Donovan, Ron K. Pickerill and Donovan J. BlissettDonovan, S.K., Pickerill, R.K. and Blissett, D.J. 2006. Collecting invertebrate tracefossils. The Geological Curator 8(5): 205-210.Trace fossils result from the behavioural activities between organisms and variablesubstrates. They form an integral part of the collections of many natural historymuseums, providing exciting specimens for display and important material for scientificresearch. Ichnofossils preserved parallel to stratification in sedimentary rocks can becollected in large slabs either from float or liberated by hammering or rock saw. Laterallyextensive specimens commonly have a repetitive morphology, so a fragment mayprovide ample data for identification and description. The morphology of an ichnofossilthat cross-cuts stratification will be more difficult to recognise in the field and mayrequire laboratory preparation of slabs using a rock saw. Bioerosive structures in or onlitho- or bioclasts may be easy to collect, but care must be taken to collect data relatingto provenance, that is, whether the clasts are autochthonous or allochthonous.Stephen K. Donovan, Department of Palaeontology, Nationaal Natuurhistorisch Museum,Postbus 9517, NL-2300 RA Leiden, The Netherlands; e-mail: donovan@naturalis.nnm.nl,Ron K. Pickerill and Donovan J. Blissett, Department of Geology, University of NewBrunswick, Fredericton, New Brunswick, Canada E3B 5A3; e-mail: rpickeri@unb.ca.Received 5th July 2005.IntroductionWhy collect trace fossils? After all, they are notfossils in the ‘true’ sense, but sedimentary structuresof one sort or another, generated by organic activity.Nevertheless, they are treated as palaeontologicalobjects and have a scientific value equivalent to thatof other geological specimens. Natural historymuseums should acquire specimens of trace fossilsfor all the reasons that they want body fossils (Knell1999; Allmon 2005), including the accumulation ofexceptional examples for display and the preservationof name-bearing types (see also Pickerill 1994;International Commission on ZoologicalNomenclature 1999).The trace fossils considered in this contribution arethose macroscopic structures generated byinvertebrates and not, for example, microscopicarthropod coprolites (e.g., Blau et al. 1997) ormicroborings (e.g., Radtke 1991). The specimens ofinterest are those that are commonly formed either ator subsequent to the time of sedimentary depositionor lithification, either parallel to (trails, tracks, someburrows) or cross-cutting stratification (manyburrows); and borings and other bioerosive structuresin hard substrates (commonly rock (particularlylimestone), shells and bones).-205-Invertebrate trace fossils, as discussed herein, can bedivided into two broad groups: those preserved inwhat was originally ‘soft’ (unlithified) sediment (or,rarely, weathered rock; P.J. Orr, writtencommunication), but which is now a lithifiedsedimentary rock, such as burrows, tracks and trails;and bioerosive structures in what were hard substratesat the time of trace formation, principally boringsinto limestones, shells and bones. Both groups caninclude trace fossils preserved in analogous spatialrelationships to substrate, such as tracks, trails andburrows parallel to bedding, and borings on or withinancient hardgrounds or other lithic substrates, suchas unconformities. Herein, we adopt the artificial‘convention’ of considering trace fossils with respectto their orientation to stratification, parallel and nonparallel, to which is added bioerosive structures inlitho- and bioclasts.Useful general references for understanding theterminology of trace fossils include Häntzschel(1975), Frey (1975), Maples and West (1992),Donovan (1994), Bromley (1996) and McIlroy (2004).Terminology of trace fossil morphology used hereinfollows these references and generally accepteddescriptive criteria used throughout palaeontology.We do not discuss the many methodologies that aregenerally applicable to palaeontological and
Figure 1. Field photograph of an outcrop in the Miocene Pelleu Island Formation, White Limestone Group, Jamaicadepicting pronounced overhang of bedding plane surfaces (see Blissett and Pickerill 2004 for details on the ichnotaxa).geological collecting, and which are adequatelydescribed elsewhere (e.g., Rixon 1976). Further, werecommend Feldmann et al. (1989) for techniques ofpreparation, which are not discussed herein. Illustratedspecimens are deposited in the collections of theNationaal Natuurhistorisch Museum, Leiden, TheNetherlands (RGM), and the Geology Museum,University of the West Indies, Mona, Kingston,Jamaica (UWIGM).Collecting specimens oriented parallel ornear-parallel to stratificationThis group embraces surface tracks and trails, certainburrows and burrow systems, and surface etchings,borings, etc., on hardground surfaces. It also includesopen infaunal burrow systems cast on the sole of thesucceeding bed in turbidites and tempestites,commonly found in, for example, Paleodictyon. Suchtraces are best seen at sites where extensive beddingplanes are exposed (tops of beds, except where theyhave been inverted by tectonic activity) or in extensivevertical sections with more or less pronouncedoverhangs (e.g., Figure 1). In many cases these arethe easiest of trace fossils to recognise, yet they arenot necessarily the easiest to collect, such as wherethe trace fossil is situated in the centre of a surface orthe bed is more than a few tens of mm in thickness. Anextensive bedding surface (e.g., Figure 2) with avariety of traces and other sedimentary structures canbe a spectacular display specimen, even if it has to becollected as a jigsaw of separate fragments for reassembly,broken up in the field by heavy hammeringor perhaps even a rock saw; a less destructivemethodology would be to cast the surface in the field.Important data, apart from that normally collected inthe field (Tucker 1982), includes labelling the topand bottom of the slab(s) (there may be differentassemblages of traces on each surface), compassorientation, and numbering the separate pieces of a‘jigsaw’ that can be related to an explanatory sketch(for suggestions of how to glue a rock ‘jigsaw’ backtogether, see Wolberg 1989). The parts of a ‘jigsaw’may include pieces of burrow infill which have‘popped off’ of a bedding plane.Collecting in situ specimens from bedding planes islikely to involve intensive labour, using a heavyhammer and/or a rocksaw. It is easier (and lessdestructive to an exposure) to look for loose slabs at-206-
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TRACE FOSSILS - THE POOR RELATIONS
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amount of space needed to accommoda
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DONOVAN, S.K., PICKERILL, R.K. and
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TRACE FOSSILS IN TWO NORTH AMERICAN
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One time was by a biology student w
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eggs, are displayed just above, nex
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Figure 8. This Early Cretaceous tra
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