A trace fossil, also ichnofossil, is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or mineralization. Ichnology is the study of such trace fossils and is the work of ichnologists.
Trace fossils are classified in various ways for different purposes. Traces can be classified taxonomically, ethologically, and toponomically, that is, according to their relationship to the surrounding sedimentary layers. Except in the rare cases where the original maker of a trace fossil can be identified with confidence, phylogenetic classification of trace fossils is an unreasonable proposition.
The Kaili Formation is a stratigraphic formation which was deposited during the Lower and Middle Cambrian. The formation is approximately 200 metres (660 ft) thick and was named after the city Kaili in the Guizhou province of southwest China.
Diplichnites are arthropod trackways with two parallel rows of blunt to elongate, closely spaced tracks oriented approximately perpendicularly to the mid-line of the trackway. The term is more often used for the ichnofossils of this description; however, similar trackways from recent arthropods are sometimes given this name as well.
Skolithos is a common trace fossil ichnogenus that is, or was originally, an approximately vertical cylindrical burrow. It is produced by a variety of organisms in shallow marine environments globally and appear as lineated features in sedimentary rocks.
Asteriacites is the name given to five-rayed trace fossils found in marine sedimentary rocks. They record the burrows of ophiuroid and asteroid sea stars on the sea floor. Asteriacites are found in European and American rocks, from the Ordovician period onwards, and are especially numerous in the Triassic and Jurassic systems.
An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited.
The "Cambrian substrate revolution" or "Agronomic revolution", evidenced in trace fossils, is the diversification of animal burrowing during the early Cambrian period.
Oldhamia is an ichnogenus describing burrows produced by worm-like organisms mining underneath microbial mats. It was common from the Early Cambrian deep-water deposits.
Diplocraterion is an ichnogenus describing vertical U-shaped burrows having a spreite between the two limbs of the U. The spreite of an individual Diplocraterion trace can be either protrusive or retrusive. Some ichnospecies have both types. The presence/absence of funnel-shaped openings should not be used as an ichnotaxobase due to the high probability that the upper portions of the trace may have been eroded away. Observation of the orientation of Diplocraterion in the field is frequently used to determine the way up of rock strata at outcrop.
Gordia marina is a lower Cambrian ichnofossil, and is the most common trace fossil in the Kaili biota displaying "smooth, cylindrical or subcylindrical, non-branching, winding and irregularly curving burrows, commonly self-overcrossing". Probably made by a worm-like creature displaying fodinichnial behaviour. It takes the form of unlined, curving parallel-walled burrows that often end with a nub, probably created as the creature probed the over- or under-lying sediment. It resembles Helminthopsis and Haplotichnus.
Ophiomorpha is an ichnotaxon, usually interpreted as a burrow of an organism living in the near-shore environment. The burrow lining is more or less smooth on the inside, and densely to strongly mammalated or nodose on the outside, due to the packing of fecal pellets for support of the burrow. Branching is irregular but Y-shaped where present. It is often considered part of the Skolithos ichnofacies, where it has occurred since the early Permian, though it has also occurred in deep water settings since the Late Jurassic, such as well-oxygenated turbidites.
Macaronichnus is an ichnogenus of trace fossil.
Haplotichnus is an ichnogenus of invertebrate trace fossil that was erected by S.A. Miller in 1889. Buatois et al. (1998) proposed that Haplotichnus should be synonymized with Gordia because both exhibit a looping course with self-crossing. Other researchers, such as Wang et al. (2009), have maintained the distinction between the two ichnogenera because Haplotichnus has sharp bends, whereas those of Gordia are not sharp. Most recently, Getty and Bush (2016) synonymized Haplotichnus with Treptichnus due to the presence of bifurcating projections at the bends. Other features, such as the looping course of the trace, thought to distinguish Haplotichnus from Treptichnus, are actually seen in one of the syntypes of Treptichnus, further supporting Getty and Bush's (2016) synonymy.
Chondrites is a trace fossil ichnogenus, preserved as small branching burrows of the same diameter that superficially resemble the roots of a plant. The origin of these structures is currently unknown. Chondrites is found in marine sediments from the Cambrian period of the Paleozoic onwards. It is especially common in sediments that were deposited in reduced-oxygen environments.
Blackberry Hill is a Konservat-Lagerstätte of Cambrian age located within the Elk Mound Group in Marathon County, Wisconsin. It is found in a series of quarries and outcrops that are notable for their large concentration of exceptionally preserved trace fossils in Cambrian tidal flats. One quarry in particular also has the distinction of preserving some of the first land animals. These are preserved as three-dimensional casts, which is unusual for Cambrian animals that are only lightly biomineralized. Additionally, Blackberry Hill is the first occurrence recognized to include Cambrian mass strandings of scyphozoans (jellyfish).
Nereites is a genus of trace fossil. Modern tracemakers of incipient Nereites include worm-like organisms, horseshoe crabs and hermit crabs. Traditionally, two models have been proposed for Nereites:
- in the ‘worm model’, Nereites is a feeding burrow produced by wormlike organisms, probing and backfilling laterally
- in the ‘arthropod model’, the characteristic lobes are pressure-release structures made by arthropod legs. According to this interpretation, Nereites is a locomotion trail
Spreite, meaning leaf-blade in German is a stacked, curved, layered structure that is characteristic of certain trace fossils. They are formed by invertebrate organisms tunneling back and forth through sediment in search of food. The organism moves perpendicularly just enough at the start of each back-and-forth pass so that it avoids reworking a previously tunneled area, thereby ensuring that it only makes feeding passes through fresh, unworked sediment.
Mesón Group is a Cambrian to Early Ordovician sedimentary formation located in the Argentine Northwest and nearby parts of Bolivia. The group members rest unconformably on top of the Ediacaran–Cambrian Puncoviscana Formation. According to G.F. Aceñolaza, the Mesón Basin – the sedimentary basin in which the Méson Group was deposited – was located between the Arequipa and Río de la Plata Cratons.
This article records new taxa of trace fossils of every kind that are scheduled to be described during the year 2019, as well as other significant discoveries and events related to trace fossil paleontology that are scheduled to occur in the year 2019.
