Stratinomical description of trace fossils

For a precise interpretation of trace fossils it is of utter importance to know their original orientation. Because the orientation is described in comparison of the strata, it is also called stratinomy (sometimes also called stratonomy, see explanation) The most used scheme for stratinomic classification was created by Seilacher (1953) and modified by Martinsson (1970). Both schemes are compared with each other in Fig. 1. Seilacher’s classification-approach was based on strata that have a higher resistence against erosion (e.g. a sandstone or limestone bed) and therefore are preserved more often. Traces or trace fossils that are preserved as reliefs (so called “semirelief”) on the top-surface of the (more erosion resistent) stratum are called epirelief (Seilacher 1953) or epichnia (Martinsson 1970) and the ones on the lower surface hyporelief (Seilacher 1953) or hypichnia (Martinsson 1970). Further divisions are made if a trace (fossil) is preserved as a bulge (“positve” after Seilacher; “convex” after Martinsson) or as a notch (“negative” after Seilacher; “concave” after Martinsson) in a sediment surface.


Fig. 1: Stratinomy of trace fossils in the classifications by Seilacher (1953) and Martinsson (1970). Modified from Rindsberg (2012).

Fully, three-dimensionally preserved traces with clear outlines were called “full reliefs” by Seilacher. They can be preserved as “originals” or as  casts of the original cavity. In contrast to Martinsson (1970), Seilacher did not distinguish between full-form traces inside or outside the more resistent stratum. Traces inside the more resistent bed are called endichnia and the ones outside exichnia in the Martinsson-classification (they then usually are filled with a more resistent sediment).
Amongst trace fossils, the ones that were made inside the sediment (endogenic) are more abundant because normal sedimentation processes and bioturbation (movement of sediment particles by organisms) usually erase all kinds of surface traces at the water/air-sediment boundary. These endogenic traces also include some that were produced on contact-surfaces between two different lithologies (e.g. claystone and sandstone). After weathering and erosion of an underlying claystone, the traces originally produced inside the ground at the contact-surface between the clay- and sandstone, will now appear to be a surface trace on the claystone but casted as a hypichnion in sandstone (just to give an example in how difficult the interpretation of a trace fossil can be and most of the time is...) However, that is exactly the reason why we need to be very precise in describing the trace fossils! Wrong or lacking description will lead to wrong interpretation and then the trace fossil has no value any more).
Endogenic forms dominate in the fossil record they usually show sharper outlines and internal structures. In the neoichnology (Ichnology of Recent times), however, exogenic traces dominate that only rarely are preserved as fossils. These are usually much more vague and softer in their outlines.
If Recent and fossil traces are compared, the fossil ones usually show sharper outlines and clearer defined internal structures. This is one of the reasons why the International Code for Zoological Nomenclature does not allow to erect new ichnotaxa on the basis of Recent traces.

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Stratinomy vs. stratonomy
"Stratinomy" is the more commonly used form and is in its word-creation analogous with stratigraphy, but "stratonomy" is said to be technically and grammatically more correct. The latter being analogous with astronomy, synonymy, taxonomy, etc. An added complication is the fact that  "stratonomy" is also used in business. Both terms are bastard  compounds of Latin strat- and Greek -nomy, and in my opinion stratinomy is the more correct form because the Latin strat- (= "covering"), takes an -i- as bridge (as in  "stratigraphy"). There is a Greek stem strat- but it means "army" (as in strategy, stratography, the latter referring to  the way armies are managed). Connecting vowels are treated in ICZN (3rd  edition, 1985, appendix D.VII - I don't have the 4th edition at hand). Latin compounds take an -i-, Greek compounds an -o-. What is  "stratinomy"? Well, in the words used above, taxonomy, astronomy,  synonymy are all Greek. Stratigraphy is a bastard but it is put together the way that a Roman would have done. So it is correct enough, and so  is stratonomy.

[Andrew K. Rindsberg, written communication, August 2013]

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