| Conostichus Temporal range: | |
|---|---|
Trace fossil classification  | |
| Ichnogenus: | † Conostichus Lesquereux, 1876 |
| Type ichnospecies | |
| Conostichus omatus Lesquereux, 1876 | |
| Ichnospecies [2] | |
| |
Conostichus is an ichnogenus of cnidarian trace fossil. [3] [4] They are nowadays considered to represent a burrow structure serving as a holdfast for an anemone-like organism. [1]
Conostichus is a plug-shaped vertical trace fossil, with a diameter varying from half to double the height. [1] Transverse constrictions and longitudinal fluting may be present, while the burrow fills occasionally show concentric laminae. The apex bears a twelve-fold symmetry, with the apical disc varying from small in C. broadheadi to broad and flat in C. typicus. [5]
The fossils display a wide variety of preservation modes, with well-preserved specimens being found alongside poorly preserved ones. The former are believed to be the result of rapid infilling with fine-grained carbonate particles, while the latter would have been passively filled with coarser carbonate sediments. [6]
Before being identified as a trace fossil, Conostichus was variously interpreted as a calcareous algae, or as a body fossil that decayed after being covered in sediment, and was later filled by another type of sediment. [7] Branson (1961) classified Conostichus as part of Scyphomedusae, interpreting the fossils as representing a basal disk and lappets corresponding to the strobilation stage of modern scyphozoans. [3] This hypothesis was later criticized, as it could not explain why the successive cones observed in Conostichus fossils did not share the same center and size, and were separated by layers of clay. [8]
They are now believed to be trace fossils made by relatives of Actinaria, possibly close to the Halcampoididae. [1]
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.
A trace fossil, also known as an ichnofossil, is a fossil record of biological activity by lifeforms but not the preserved remains of the organism 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. The study of such trace fossils is ichnology and is the work of ichnologists.
Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and fish; it can occur on coastlines, on coral reefs, and on ships; its mechanisms include biotic boring, drilling, rasping, and scraping. On dry land, bioerosion is typically performed by pioneer plants or plant-like organisms such as lichen, and mostly chemical or mechanical in nature.
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.
Paleodictyon is a trace fossil, usually interpreted to be a burrow, which appears in the geologic marine record beginning in the Precambrian/Early Cambrian and in modern ocean environments. Paleodictyon were first described by Giuseppe Meneghini in 1850. The origin of the trace fossil is enigmatic and numerous candidates have been proposed.
Cruziana is a trace fossil consisting of elongate, bilobed, approximately bilaterally symmetrical burrows, usually preserved along bedding planes, with a sculpture of repeated striations that are mostly oblique to the long dimension. It is found in marine and freshwater sediments. It first appears in upper Fortunian rocks of northern Iran and northern Norway. Cruziana has been extensively studied because it has uses in biostratigraphy, and because the traces can reveal many aspects of their makers' behavior.
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.
Skolithos is a common trace fossil ichnogenus that is, or was originally, an approximately vertical cylindrical burrow with a distinct lining. It was produced globally by a variety of organisms, mostly in shallow marine environments, and appears as linear features in sedimentary rocks.
An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited.
Arenicolites is a U-shaped ichnotaxon dating from Ediacaran times onwards in South Australia. The trace shown by this fossil, is a pair of closely spaced circles on a bedding plane. In vertical section the traces are U- or J-shaped. They appear to be burrows made by a kind of worm.
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 nodules 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.
Conichnus is an ichnogenus of trace fossil.
Shallow water marine environment refers to the area between the shore and deeper water, such as a reef wall or a shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below. The water in this environment is shallow and clear, allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.
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.
Anthony J. Martin is a paleontologist who has taught at Emory University since the early 1990s. He is best known for his books, An Introduction to the Study of Dinosaurs, Life Traces of the Georgia Coast, Dinosaurs without Bones, and Life Sculpted: Tales of the Animals, Plants, and Fungi that Drill, Break, and Scrape to Shape Earth. He is married to artist Ruth Schowalter.
Pholad borings are tubular burrows in firm clay and soft rock that have been created by bivalve molluscs in the family Pholadidae. The common names of clams in this family are "pholads", "piddocks", and "angel wings"; the latter because their shells are white, elongated and tend to be shaped like a wing and have sculpture somewhat reminiscent of a wing.
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.
Muensteria is the ichnogenus of a type of trace fossil that is found in sedimentary rocks, and is thought to represent the horizontal burrow of a marine invertebrate organism. It is a horizontal, non-branching, unlined, tube-like burrow characterized by menisci, which are concave to flat laminae within the burrow created as the organism packs sediment and fecal material behind it when moving forward in the burrow. Muensteria is one example of a meniscate burrow.
Solecurtus strigilatus, also known as the rosy razor clam, is a species of saltwater clam, a marine bivalve mollusc in the family Solecurtidae. This mollusc is a suspension feeder and can burrow with great rapidity to escape predators. It is an unusual bivalve in that its shell valves are too small to contain all the soft tissue, and the animal is unable to retreat into its shell.
Bergaueria is an Ediacaran–Silurian trace fossil believed to represent the dwelling trace of Cnidarians. It likely caused mixing and fluid exchange into the sediment (bioirrigation). Similar traces (Cheiichnus) can be made by rotational movement of arthropods.