Trace fossil Totally Explained

Everything about Trace Fossil totally explained

Trace fossils, also called ichnofossils ( meaning "trace" or "track"), are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings (bioerosion), 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 fossilised remains of parts of organisms' bodies, usually altered by later chemical activity or mineralisation.
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.

Domichnia, dwelling structures reflecting the life position of the organism that created it.
Fodinichnia, three-dimensional structures left by animals which eat their way through sediment, such as deposit feeders;
Pascichnia, feeding traces left by grazers on the surface of a soft sediment or a mineral substrate;
Cubichnia, resting traces, in the form of an impression left by an organism on a soft sediment;
Repichnia, surface traces of creeping and crawling.

Fossils are further classified into form genera, a few of which are even subdivided to a "species" level. Classification is based on shape, form, and implied behavioural mode.

Information provided by ichnofossils

Because identical fossils can be created by a range of different organisms, trace fossils can only reliably inform us of two things: the consistency of the sediment at the time of its deposition, and the energy level of the depositional environment.

Paleoecology

Trace fossils provide us with indirect evidence of life in the past, such as the footprints, tracks, burrows, borings, and feces left behind by animals, rather than the preserved remains of the body of the actual animal itself. Unlike most other fossils, which are produced only after the death of the organism concerned, trace fossils provide us with a record of the activity of an organism during its lifetime.
   Trace fossils are formed by organisms performing the functions of their everyday life, such as walking, crawling, burrowing, boring, or feeding. Tetrapod footprints, worm trails and the burrows made by clams and arthropods are all trace fossils.
   Perhaps the most spectacular trace fossils are the huge, three-toed footprints produced by dinosaurs and related archosaurs. These imprints give scientists clues as to how these animals lived. Although the skeletons of dinosaurs can be reconstructed, only their fossilized footprints can determine exactly how they stood and walked. Such tracks can tell much about the gait of the animal which made them, what its stride was, and whether or not the front limbs touched the ground.
   However, most trace fossils are rather less conspicuous, such as the trails made by segmented worms or nematodes. Some of these worm castings are the only fossil record we've of these soft-bodied creatures.

Palæoenvironment

Fossil footprints made by tetrapod vertebrates are difficult to identify to a particular species of animal, but they can provide us with valuable information such as the speed, weight, and behavior of the organism that made them. Such trace fossils are formed when amphibians, reptiles, mammals or birds walked across soft (probably wet) mud or sand which later hardened sufficiently to retain the impressions before the next layer of sediment was deposited. Some fossils can even provide details of how wet the sand was when they were being produced, and hence allow estimation of palæo-wind directions.
Assemblages of trace fossils occur at certain water depths,
The base of the Cambrian period is defined by the first appearance of the trace fossil Trichophycus pedum.
Trace fossils have a further utility as many appear before the organism thought to create them, extending their stratigraphic range.

Ichnofacies

Trace fossil assemblages are far from random; the range of fossils recorded in association is constrained by the environment in wheich the trace-making organisms dwelt. however their uneven width and tapering ends make a biological origin difficult to defend. The first evidence of burrowing which is widely accepted dates to the Ediacaran period, around . During this period, burrows are horizontal, or just below the surface. Such burrows must have been made by motile organisms with heads, which would probably have been bilateran animals. The burrows observed imply simple behaviour, and the complex, efficient feeding traces common from the start of the ensuing Cambrian period are absent. Some Ediacaran fossils, especially discs, have been interpreted tentatively as trace fossils, but this hypothesis hasn't gained widespread acceptance. As well as burrows, some trace fossils have been found directly associated with an Ediacaran fossil. Yorgia and Dickinsonia are often found at the end of long pathways of trace fossils matching their shape; the method of formation of these disconnected and overlapping fossils largely remains a mystery. The potential mollusc Kimberella is associated with scratch marks thought to have been formed by its radula, further traces from appear to imply active crawling or burrowing activity. and traces normally attributed to arthropods. These represent a “widening of the behavioural repertoire”, both in terms of abundance and complexity.
   Trace fossils are a particularly significant source of data from this period because they represent a data source that isn't directly connected to the presence of easily-fossilized hard parts, which are rare during the Cambrian. Whilst exact assignment of trace fossils to their makers is difficult, the trace fossil record seems to indicate that at the very least, large, bottom-dwelling, bilaterally symmetrical organisms were rapidly diversifying during the early Cambrian.
   Further, less rapid diversification occurred since, and many traces have been converged upon independently by unrelated groups of organisms. Bioerosion through time has produced a magnificent record of borings, gnawings, scratchings and scrapings on hard substrates. These trace fossils are usually divided into macroborings and microborings. Bioerosion intensity and diversity is punctuated by two events. One is called the Ordovician Bioerosion Revolution (see Wilson & Palmer, 2006) and the other was in the Jurassic. For a comprehensive bibliography of the bioerosion literature, please see the External links below. The oldest types of tetrapod tail-and-foot prints date back to the latter Devonian period. These vertebrate impressions have been found in Ireland, Scotland, Pennsylvania, and Australia.
   Important human trace fossils are the Laetoli (Tanzania) footprints, imprinted in volcanic ash 3.7 million years ago (mya) -- probably by an early Australopithecus.

Confusion with other types of fossils

Trace fossils shouldn't be confused with body casts. The Ediacara biota, for instance, primarily comprises the casts of organisms in sediment.
Early geologists gave the name 'fucoid' to a wide variety of markings they found on the bedding planes of sedimentary rocks. The earth scientists frequently misinterpreted these 'fucoid' marks as being the fossilized remains of seaweed. However, in more recent years, these markings have been studied with greater thoroughness. It is now apparent that the 'fucoids' and other markings have in fact been caused by a variety of plants and animals. As a result, these 'fucoid' markings are now termed trace fossils. Pseudofossils, which are not true fossils, should also not be confused with ichnofossils, which are true indications of prehistoric life. Image:FaringdonCobble.JPG|Numerous borings in a Cretaceous cobble, Faringdon, England; see Wilson (1986). Image:BoredEncrustedShell.JPG|Sponge borings and encrusters on a modern bivalve shell, North Carolina. Image:Helminthopsis01.JPG|Helminthopsis ichnosp.; a trace fossil from the Logan Formation (Lower Carboniferous) of Wooster, Ohio. Further Information

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