Continental trace fossils and museum exhibits - Geological Curators ...

‘forgotten’. The Natural History Museum in London(BMNH) has a good collection of trace fossils and yetfor years these specimens were in a state which wasless than user-friendly. Only when resources wereavailable, in the form of unpaid volunteers supervisedby hard-pressed museum staff, did the curatoriallevel of the collection rise and improve to a moreusable state. The collection is small relative to manyother taxa in the department, only occupying about1.6 % of the storage area of one floor, not includinglarger traces like dinosaur tracks/trackways whichhave to be stored elsewhere within the Museumcomplex, nor other smaller traces which are keptalongside their known and recognised formingorganisms.A further consequence of ‘Cinderella’ groups liketrace fossils is that a good collection made by anenthusiast is unlikely to be received with muchenthusiasm by a museum whose storage space islimited. This may lead to the collection being lost toscience.However, trace fossils, especially when placed intheir sedimentological and palaeobiological context,are important environmental and ecologicalindicators. They are useful for trying to determinesuch things as the mode of life, even if the organismitself was either not preserved or unknown. Forexample, the carpoid Rhenocystis from the Devonianof Bundenbach in Germany belongs to a group thathave been the subject of debate concerning theirfunctional morphology and mode of life; even suchbasic characteristics as life orientation are contended.Jefferies (1984) provided detailed descriptions of hisinterpretation of the movement of the organism thatis now supported by the discovery of severalspecimens of Rhenocystis at the end of their trails(Sutcliffe et al. 2000). Even when the ichnotaxa arewell documented and their relationships are known,e.g., the Diplichnites-Cruziana-Rusophycussequence, the evidence of the actual producers isscanty. Although the producing organism may befound at the end of the trail (for example, a trilobite),there are other organisms in entirely separatetaxonomic groups that produce very similar tracefossils (see discussion in Whittington 1992, p. 39).Correlating the two is very difficult, but the interestand benefits of doing so are great. So why is thereonly limited interest in trace fossils? The reasonsmight include any or all of the following.• Collections failure - people do not recognisethem or they cannot be extracted from theirlocalities (Donovan et al. 2006).• Too big to collect and/or store.• Not aesthetic - trace fossils are generallyconsidered unattractive, although ichnotaxa suchas Zoophycos and Paleodictyon, for example, arenonetheless pleasing to the eye.• Not identifiable - they require a good deal ofexpertise to appreciate their importance (althoughthis may be said for many fossil groups).Suggestions for organising trace fossilcollectionsTrace fossils are morphological and functional entitieswith the overlay of a Linnean style of classification,distinguished from true biological taxonomy by theprefix ‘ichno’ - ichnogenus or ichnospecies. They arenot body fossils in the biological sense, but are thetraces produced by the organisms in the course ofliving, that is, sedimentary structures. In order that acollection can be useful some form of organisationneeds to be imposed upon the specimens. Variousalternatives are possible.• Alphabetical (commonly by ichnogenus) – Thesimplest organisation and one that enables aconstant layout to be made of ichnogenera.Revision of the interpretation of the traces wouldnot lead to major problems of reorganisation forcurators, unless an ichnogenus is ‘split’ orsynonymised. This is currently the way in whichspecimens are organised in the BMNH. It has theadvantage of not requiring constant reorganisationaccording to differing interpretations,and is usable by expert and novice alike.• Stratigraphical – Trace fossils can be restrictedto certain stratigraphic levels, so that astratigraphical organisation will reflect theirdifferent morphologies and likely producers, ormay occur at many horizons (some taxa occurthroughout the Phanerozoic).• Geographical – Organisation according tolocation will show similarities and groupingsover large areas, may help to correlate stratigraphichorizons and will support ichnofaunal studies.• Ethological – Organisation follows a functionalinterpretation of ichnotaxa. Similar modes ofproduction are grouped together, such as feedingtraces, dwelling traces, locomotion traces, etc.Problems may arise when interpretations ofbehaviour change, which will probably give acurator problems of reorganisation.• Combination – An assembly of these can also beused, though this will inevitably increase the-256-