Trace fossil

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A trace fossil, also known as an ichnofossil ( /ˈɪknoʊfɒsɪl/; from Greek: ἴχνος ikhnos "trace, track"), is a fossil record of biological activity by lifeforms but not the preserved remains of the organism itself.^[1] Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or by mineralization. The study of such trace fossils is ichnology - the work of ichnologists.^[2]

Trace fossils may consist of physical impressions made on or in the substrate by an organism.^[3] For example, burrows, borings (bioerosion), urolites (erosion caused by evacuation of liquid wastes), footprints, feeding marks, and root cavities may all be trace fossils.

The term in its broadest sense also includes the remains of other organic material produced by an organism; for example coprolites (fossilized droppings) or chemical markers (sedimentological structures produced by biological means; for example, the formation of stromatolites). However, most sedimentary structures (for example those produced by empty shells rolling along the sea floor) are not produced through the behaviour of an organism and thus are not considered trace fossils.

The study of traces – ichnology – divides into paleoichnology, or the study of trace fossils, and neoichnology, the study of modern traces. Ichnological science offers many challenges, as most traces reflect the behaviour – not the biological affinity – of their makers. Accordingly, researchers classify trace fossils into form genera based on their appearance and on the implied behaviour, or ethology, of their makers.