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Trace fossils, also called ichnofossils (sg. ; (ギリシア語:ιχνος) ''ikhnos'' "trace, track"), are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings (bioerosion), urolites (erosion caused by evacuation of liquid wastes), footprints and feeding marks, and root cavities. 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 — or sedimentological structures produced by biological means - for example, stromatolites. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or mineralization. Sedimentary structures, for example those produced by empty shells rolling along the sea floor, are not produced through the behaviour of an organism and not considered trace fossils. The study of traces is called ichnology, which is divided into ''paleoichnology'', or the study of trace fossils, and ''neoichnology'', the study of modern traces. This science is challenging, as most traces reflect the behaviour — not the biological affinity — of their makers. As such, trace fossils are categorised into form genera, based upon their appearance and the implied behaviour of their makers. ==Occurrence== Traces are better known in their fossilised form than in modern sediments.〔 This makes it difficult to interpret some fossils by comparing them with modern traces, even though they may be extant or even common.〔 The main difficulties in accessing extant burrows stem from finding them in consolidated sediment, and being able to access those formed in deeper water. Trace fossils are best preserved in sandstones;〔 the grain size and depositional facies both contributing to the better preservation. They may also be found in shales and limestones.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Trace fossil」の詳細全文を読む スポンサード リンク
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