When most people think of fossils they probably focus on bones and shells but of course there is much more available to palaeontologists than just these with things like nests, coprolites and footprints also abounding. Although the split is rather one of convenience and lacking one of strict definition the former are classically termed body fossils and the latter trace fossils. Essentially, the actual remains of organisms come under the term ‘body fossil’ whether it be bone, shell, soft tissues or whatever, and marks left behind by organism (typically recording some aspect of behaviour) are termed ‘trace fossils’.
The split is of course awkward at best. While footprints or swimming traces are pretty strictly trace fossils and a typical skeleton or ammonite would be a body fossil it rapidly gets tricky. Eggs could be termed body fossils in their own right (certainly those containing embryos probably should) but as part of a nest they are closer to trace fossils as are the fragments of hatched eggs, and something like stomach contents or the fighting dinosaurs could easily be considered both. Finally there are odd, ‘unintentional’, traces like those made by old shells rolling around on a sea floor which while leaving a mark are hardly indicative of behaviour yet probably still fall under the heading of traces.
Still it’s useful to have a handle on such definitions since they do crop up and I’m aware that despite my goal to keep this blog as accessible as possible I use terms that are not in common usage or are not clearly defined. I’m trying to fill some of those gaps in where I can, but it can be very dull to write and hard to remember what I have and have not covered.
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