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  BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, researchlibraries, and research funders in the common goal of maximizing access to critical research. Ichnotaxobases for Bioerosion Trace Fossils in Bones Author(s): Cecilia A. Pirrone , Luis A. Buatois , and Richard G. BromleySource: Journal of Paleontology, 88(1):195-203. 2014.Published By: The Paleontological SocietyDOI: BioOne ( is a nonprofit, online aggregation of core research in the biological, ecological, andenvironmental sciences. BioOne provides a sustainable online platform for over 170 journals and books publishedby nonprofit societies, associations, museums, institutions, and presses.Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiriesor rights and permissions requests should be directed to the individual publisher as copyright holder.  ICHNOTAXOBASES FOR BIOEROSION TRACE FOSSILS IN BONES CECILIA A. PIRRONE, 1 LUIS A. BUATOIS, 2 AND RICHARD G. BROMLEY 3 1 Departamento de Paleontologı´a, Instituto Argentino de Nivologı´a, Glaciologı´a y Ciencias Ambientales (IANIGLA), CCT-CONICET-Mendoza, Av.Ruiz Leal s/n 5500 Mendoza, Argentina,  ,  . ;  2 Department of Geological Sciences, University of Saskatchewan,114 Science Place SK S7N 5E2 Saskatoon, Canada,  , . ; and   3 Geological Museum–SNM, Øster Voldgade 5–7 DK-1350Copenhagen, Denmark,  ,  . A BSTRACT  —Bioerosion trace fossils in bones are defined as biogenic structures that cut or destroy hard bone tissue as theresult of mechanical and/or chemical processes. Under the premise that their paleoecological potential can completely berealized only through correct taxonomic assignment, this work focuses on the methodology for naming these biogenicstructures. Thus, we propose the following ichnotaxobases in order to assist in naming trace fossils in bones: generalmorphology, bioglyphs, filling, branching, pattern of occurrence, and site of emplacement. The most common generalmorphologies are: pits and holes (borings); chambers; trails; tubes; channels (canals); grooves; striae; and furrows. Themain types of bioglyphs are grooves and scratches, which may display different arrangements, such as parallel and opposing, or arcuate paired. The nature of the fill may help recognition of the srcin, composition, and relationship with thesurrounding sediment, as well as processes of destruction or consumption of bony tissue. The structure and layout of thefilling, such as meniscate backfill or pelleted filling, offer information about the bioeroding processes. Branchingstructures on cortical bone are present in canals and furrows. Where the trace penetrates spongy bone, branching structuresare forming tunnels that may connect internal chambers. The common patterns of occurrence are individual, paired,grouped, overlapping, lined, and arcuate. The site of emplacement may be in cortical bone, spongy bone, articular surfaces,internal bone microstructures, and external bone anatomical structures. The use of substrate as an ichnotaxobase is problematic, but as biological substrate, bone itself is a valuable source of information for paleoecologic and ethologicinferences. Given the paleontological importance of bioerosion trace fossils in bones, we underscore interactions betweenichnology and other sciences, such as forensic entomology, archaeology, paleoecology, and taphonomy. INTRODUCTION D URING RECENT  years, bioerosion trace fossils in bones have been mostly used as tools to decipher aspects of theidentity and paleoecology of their producers (Cruickshank,1986; Currie and Jacobsen, 1995; Martin and West, 1995;Jacobsen, 1998; Tanke and Currie, 2000; Rogers et al., 2003;Hone and Rauhut, 2010; Xing et al., 2012). Many authors haverecognized their importance in reconstructing the taphonomic processes involved, particularly during the first stages of decay,and the implications of bioerosion in bone preservation(Behrensmeyer, 1978; Behrensmeyer et al., 2000; Laudet and Antoine, 2004; Bader et al., 2009; Huchet et al., 2011; Backwellet al., 2012). However, with the exception of a few studies(Jacobsen and Bromley, 2009; Backwell et al., 2012), little has been published on the methodology for naming bioerosion tracefossils in bones. An ichnotaxobase is a distinctive morphologicfeature of a trace fossil that displays significant and readilydetectable variability and, therefore, is commonly used inichnotaxonomic classifications (Bromley, 1996; Buatois and Ma´ngano, 2011). Given the growing literature on trace fossils in bones, we consider that their potential can only be realized through correct taxonomic assignment and ethologic interpreta-tion. Therefore, the aims of this work are to: 1) define what isconsidered a bioerosion trace in a bony substrate, 2) defineichnotaxobases for bioerosion trace fossils in bones, and 3)discuss a set of criteria that may help distinguish these structuresfrom other kinds of non-biogenic marks commonly present on bone surfaces. In addressing these problems, we discuss thecontroversies surrounding the use of substrate as an ichnotax-obase. Abbreviations used in this paper are RTMP (RoyalTyrrell Museum of Palaeontology), MPM-Pv (Museo PadreMolina Paleontologı´a de Vertebrados, Rı´o Gallegos, SantaCruz), and IANIGLA-Icn (Instituto Argentino de Nivologı´a,Glaciologı´a y Ciencias Ambientales, Colecci ´o n de Icnologı´a,Mendoza, Argentina). DEFINING BIOEROSION TRACE FOSSILS IN BONES Bioerosion was defined as every form of biologic penetrationinto hard substrates (Neumann, 1966). When traces are related to bones, it is important to determine whether the trace fossilrepresents a true bioerosion structure rather than a bioturbationstructure in contact with the bone surface or in the associated substrate. In this paper, bioerosion trace fossils in bones aredefined as biogenic structures that cut or destroy hard osseoustissue structures as the result of mechanical and/or chemical processes (Fig. 1). On the other hand, bioturbation structures produced in the sandy substrate attached to the bone surfacemay be misidentified as bioerosion structures. Analysis of thin-section shows examples of trace fossils preserved in full relief,in host sediment, but not eroding the bone surface.  NAMING BIOEROSION TRACE FOSSILS IN BONES Although many studies have described trace fossils in bones,only a few provide a taxonomic treatment (Cruickshank, 1986;Thenius, 1988; Mikula´ ˇs  et al., 2006; Roberts et al., 2007;Jacobsen and Bromley, 2009; Mu ˜n iz et al., 2010) (Fig. 2).Regardless of its pitfalls, the ichnotaxonomic classification provides the best common ground on which to base moretheoretical elaborations and practical applications (Bromley,1996; Buatois and Ma´ngano, 2011). As stated by Bromley(1996, p. 166),  ‘‘ in the final analysis, it is the morphology of thetrace as an expression of animal behavior that is the basis of thename. ’’  In practice, it is difficult to adopt a strictly descriptive procedure for naming ichnotaxa because while morphology is195  Journal of Paleontology , 88(1), 2014, p. 195–203Copyright    2014, The Paleontological Society0022-3360/14/0088-0195$03.00DOI: 10.1666/11-058  observed, behavior is inferred (Ma´ngano et al., 2002; Buatoisand Ma´ngano, 2011 ) .In any case, a number of characteristics are frequently used for naming ichnotaxa (Bromley, 1996). Pickerill (1994) noted that the relative importance of some taxonomic characteristicsvaries widely among different types of ichnofossils. This is based on the fact that one characteristic that is used to define anichnogenus, may be in other instances used at ichnospecificlevel, or not used at all.Bioerosion structures in bones show some marked departureswith respect to some of the most common bioturbationstructures and even to the most typical bioerosion structures inother substrates. The first issue to address is why it is necessaryto propose specific characters that should be considered in thedescription and taxonomic classification of bioerosion tracefossils in bones. In the field of bioerosion, there is presently noichnotaxonomy specifically designed to accommodate tracefossils in bones. Therefore, we propose ichnotaxobases for describing bioerosion trace fossils in bones. These ichnotax-obases are not that different from the srcinal ones proposed for trace fossils in general (Bromley, 1996), but they focus on somerelevant aspects directly related to development and mecha-nisms of bioerosion. These ichnotaxobases are thought to beapplied to both vertebrate and invertebrate trace fossils. ICHNOTAXOBASES FOR BIOEROSION TRACES IN BONES The following ichnotaxobases are proposed in order to assistin naming traces in bones: 1) general morphology; 2) bioglyphs;3) filling; 4) branching; 5) pattern of occurrence; and 6) site of emplacement (Fig. 3). General morphology .—Jacobsen and Bromley (2009) noted that  ‘‘ application of ichnotaxa to trace fossils is a procedure thatmust vary according to the group of trace fossils under study. ’’ They differentiated a group of trace fossils that display relativelyconstant morphology, such as invertebrate burrows (e.g., Uch-man, 1999) and insect nests (e.g., Genise, 2004), from another group of structures that tend to show extreme variation inmorphology, such as tracks of tetrapods (e.g., Manning, 2004;Mila´n and Bromley, 2006), due to preservational or behavioraldifferences or because of variations in substrate consistency (e.g.,Bromley, 2001; Forn ´o s et al., 2002).Britt et al. (2008) proposed morphotypes and some generalmorphological categories to group trace fossils in bones attributed to insects in continental settings. Roberts et al. (2007) proposed togroup the most commonly recorded trace-fossil morphologies intofive general categories: ovoid chambers (e.g.,  Cubiculum  isp.);shallow circular to elliptical pits; star-shaped pit traces; surfacetrails (e.g.,  Osteocallis  isp.); and tunnels and subcortical cavities.The recognition of a pattern based on the shape of the biogenicstructure could be very useful for interpreting the ethology and toidentify an ichnotaxon (Fig. 4). This approach follows the view of morphology as an expression of behavior, as recommended byBromley (1996). In addition, traces produced by predation of vertebrates (e.g., tooth traces) are usually described by comparingsize and disposition of carnivorous fossil mandibles (Mikula´ ˇs  etal., 2006; Noriega et al., 2007; Jacobsen and Bromley, 2009).In this paper, we encourage the use of morphology in thediagnosis of bone bioerosion ichnotaxa, and we recommend differentiating between morphologic description and ethologicinterpretation wherever possible. The latter is vital to illuminateour understanding on the genesis of the structure, but it is notadvisable to include this in the description of an ichnotaxon. Themost common morphologic types to be considered are: pits and holes (borings); chambers; trails; tubes; channels (canals);grooves; striae; and furrows. Each of these may present differentorientation with respect to the substrate surface.  Bioglyphs .—As mentioned by Mikula´ ˇs  (1998) and Ekdale and Gibert (2010), morphologic features interpreted as bioglyphs have been used as valid ichnotaxobases for bioerosion in bones (e.g.,Hasiotis et al., 1999; Tapanila et al., 2004; Roberts et al., 2007;West and Hasiotis, 2007; Bader et al., 2009) and bioerosion inother substrates (Kelly and Bromley, 1984; Gibert and Ekdale,2010; Donovan, 2002, 2011). They provide evidence of how thetrace fossil was produced. They also can provide informationabout substrate characteristics. Ekdale and Gibert (2010) proposed revising the term bioglyph  ‘‘ to encompass only carvingsor engravings that are inscribed into the wall of a burrow or  boring. ’’  We follow their definition in our study.Because of the characteristics of bone as hard substrate and as aresult of animal activity, bioglyphs represent the clue tounderstanding specific methods and strategies of bioerosion in bones. They also can supply detailed information for interpretinganatomy and identify the producer. For these reasons, theyconstitute an important ichnotaxobase. Despite the importance of  bioglyphs as a distinctive character in ichnotaxonomy, fewichnotaxa have been erected using them as ichnotaxobase. Cubiculum ornatus  and   Osteocallis mandibulus  Roberts et al.2007 are notable exceptions. In both cases, bioglyphs wereinterpreted as the result of insect mandibles scratching or gnawing.The under-utilization of bioglyphs as an ichnotaxobase is probably due to difficulties in their recognition, especially in thecase of tunnels that penetrate into bone. Part of the problem lies inthe physical structure of certain types of bone tissues, such astrabecular and cortical. Trabecular bone is a light, porous materialenclosing numerous large spaces that give a spongy appearance.The bone matrix is organized into a three-dimensional network of  Figure  1  —The concept of bioerosion for trace fossils in bones;  1 , schematicrepresentation of different bone tissues (cortical and spongy) and theassociated trace fossils;  a–c  indicate bioerosion trace fossils affecting bonetissues at different levels (cortical and spongy bone) whereas  d   shows a bioturbation trace fossil associated with the bone surface but not eroding the bone tissue;  2 , close-up of a polished surface showing a transversal view of a bioerosion trace fossil in dinosaur cortical bone tissue; IANIGLA-Icn 11, Rı´o Neuqu ´e n Subgroup, late Turonian–late Coniacian, Mendoza Province,Argentina. 196  JOURNAL OF PALEONTOLOGY, V. 88, NO. 1, 2014  Figure  2  —List of ichnotaxa defined for bioerosion traces in bones and schematic representation of their general morphology. Trace fossils appear in black, bone-substrate in gray.  PIRRONE ET AL.—BONE BIOEROSION   197  trabeculae (plates and rods). Spaces between are commonly filled with marrow (soft tissue). In contrast to cortical bone, at amicroarchitectural scale, trabecular bone does not have a plainhard surface that allows recording of the pattern of bioglyphsresulting from macrobioerosion. Examples discussed in this paper, such as  Cubiculum ornatus,  are all emplaced in cortical bone, which can be eroded in such a way that bioglyphs arerecorded and commonly recognized. Modern technologies, suchas SEM studies (e.g., Britt et al., 2008, fig. 1, p. 63), are provinguseful in assisting recognition of bioglyphs. The main types of  bioglyphs on the walls of bioerosion trace fossils on bones aregrooves and scratches. These bioglyphs may present differentarrangements, such as parallel and opposing or arcuately paired.  Filling  .—Recognition of the presence of filling and distin-guishing passive from active filling constitutes an important toolfor reconstructing taphonomic histories and ethologic signifi-cance of biogenic structures. As active filling represents the resultof animal handling of the substrate, it usually contrasts with thesurrounding sediment and possesses a typical structure (Bromley,1996). Because of its highest significance, this ichnotaxobase has been used in the diagnosis of many bioturbation ichnotaxa(Clifton and Thompson, 1978; Pemberton and Frey, 1982).Actively filled traces, eroded into bone substrate, involve a set of complex processes that imply destruction of superficial and internal bone structures, consumption of organic matter, process-ing of waste material, and locally mixing with surrounding softsediment, especially when part of the fill resembles the hostsediment or part of bone structure is drawn out into the sediment(Paik, 2000). Therefore, analysis of the nature of the fill may helprecognition of the srcin, composition, and relationship with thesurrounding sediment, as well as processes of destruction or consumption of bony tissue. On the other hand, the structure and layout of the filling, such as meniscate backfill or pelleted filling,offer much information about the bioeroding processes, com-monly related to insect and microfauna feeding behavior. In bioerosion traces in bones, meniscate backfill could result fromthe alternation of organic matter (derived from the bone) and sediment ingestion and backfilling by the producer (Fig. 5). Bonefragments have been reported as part of the composition of filling(Paik, 2000). The presence of bone fragments in the filling, arecognizable pattern of their distribution, as well as bonefragment shape, could be also considered an ichnotaxobase, if these characteristics are interpreted as the result of a specific and recurrent behavior, namely selection or destruction of bone based  Figure  3  —Diagram illustrating the most common attributes of ichnotaxobases for bioerosion trace fossils in bones and their terminology. 198  JOURNAL OF PALEONTOLOGY, V. 88, NO. 1, 2014

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