Ichnology

A trace fossil, also ichnofossil ( /ˈɪknoʊfɒsɪl/; from Greek: ἴχνος ikhnos 'trace, track'), is a geological record of biological activity. Ichnology is the study of such traces, and is the work of ichnologists. Trace fossils may consist of impressions made on or in 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.Numerous borings in a Cretaceous cobble, Faringdon, England; see Wilson (1986).Sponge borings (Entobia) and encrusters on a modern bivalve shell, North Carolina.Entobia from the Prairie Bluff Chalk Formation (Upper Cretaceous). Preserved as a cast of the excavations.Helminthopsis ichnosp.; a trace fossil from the Logan Formation (Lower Carboniferous) of Wooster, Ohio.Gigandipus, a dinosaur footprint in the Lower Jurassic Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm, southwestern Utah.Lockeia from the Dakota Formation (Upper Cretaceous).Lockeia from the Chagrin Shale (Upper Devonian) of northeastern Ohio. This is an example of the trace fossil ethological group Fugichnia.Gnathichnus pentax echinoid trace fossil on an oyster from the Cenomanian of Hamakhtesh Hagadol, southern Israel.Naticid boring in Stewartia from the Calvert Formation, Zone 10, Calvert Co., MD (Miocene).Trace fossils as convex hyporeliefs on bottom of bed; Bull Fork Formation (Upper Ordovician); Caesar Creek, Ohio.Inverted trace fossil of an unidentified tridactyl ornithopod A trace fossil, also ichnofossil ( /ˈɪknoʊfɒsɪl/; from Greek: ἴχνος ikhnos 'trace, track'), is a geological record of biological activity. Ichnology is the study of such traces, and is the work of ichnologists. Trace fossils may consist of impressions made on or in 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 - 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. 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. Trace fossils are generally difficult or impossible to assign to a specific maker. Only in very rare occasions are the makers found in association with their tracks. Further, entirely different organisms may produce identical tracks. Therefore, conventional taxonomy is not applicable, and a comprehensive form of taxonomy has been erected. At the highest level of the classification, five behavioral modes are recognized: