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Halkieriids
The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is ''Halkieria'' , which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the small shelly fossil assemblages. The best known species is ''Halkieria evangelista'', from the North Greenland Sirius Passet Lagerstätte, in which complete specimens were collected on an expedition in 1989. The fossils were described by Simon Conway Morris and John Peel in a short paper in 1990 in the journal ''Nature''. Later a more thorough description was undertaken in 1995 in the journal ''Philosophical Transactions of the Royal Society of London'' and wider evolutionary implications were posed. The group is sometimes equated to Sachitida, although as originally envisaged, this group includes the wiwaxiids and is thus equivalent to the Halwaxiida. History of discovery Armor plates called "sclerites" had long been known as elements of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halwaxiid
Halwaxiida or halwaxiids is a proposed clade equivalent to the older orders Sachitida He 1980 and Thambetolepidea Jell 1981, loosely uniting scale-bearing Cambrian animals, which may lie in the Crown group#Stem groups, stem group to molluscs or lophotrochozoa. Some palaeontologists question the validity of the Halwaxiida clade. Definition and members The name "halwaxiid" was formed by combining the names of two members of the proposed group, ''Halkieria'' and ''Wiwaxia''. The group was defined as a set of Early to Mid Cambrian animals that had: a "chain mail" coat of three concentric bands of small armor plates that are called sclerites; in some cases, a small cap-like shell at the front end and in some cases both ends. Some scientists are unhappy with this loose definition, arguing that such traits may have arisen convergent evolution, convergently rather than being inherited from a common ancestor. This objection implies that the group may not be monophyletic, and that their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Small Shelly Fossils
The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span. Some of the fossils represent the entire skeletons of small organisms, including the mysterious '' Cloudina'' and some snail-like molluscs. However, the bulk of the fossils are fragments or disarticulated remains of larger organisms, including sponges, molluscs, slug-like halkieri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Small Shelly Fossil
The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are biomineralization, mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian period (geology), Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span. Some of the fossils represent the entire skeletons of small organisms, including the mysterious ''Cloudina'' and some snail-like molluscs. However, the bulk of the fossils are fragments or disarticulated remains of larger organisms, including spo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Growth Ring
Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed in a tree. As well as dating them, this can give data for dendroclimatology, the study of climate and atmospheric conditions during different periods in history from the wood of old trees. Dendrochronology derives from the Ancient Greek (), meaning "tree", (), meaning "time", and (), "the study of". Dendrochronology is useful for determining the precise age of samples, especially those that are too recent for radiocarbon dating, which always produces a range rather than an exact date. However, for a precise date of the death of the tree a full sample to the edge is needed, which most trimmed timber will not provide. It also gives data on the timing of events and rates of change in the environment (most prominently climate) and also in wood found in archaeology or works of art and architecture, such as old panel paintings. It is als ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sclerites
A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly to the hardened parts of arthropod exoskeletons and the internal spicules of invertebrates such as certain sponges and soft corals. In paleontology, a scleritome is the complete set of sclerites of an organism, often all that is known from fossil invertebrates. Sclerites in combination Sclerites may occur practically isolated in an organism, such as the sting of a cone shell. Also, they can be more or less scattered, such as tufts of defensive sharp, mineralised bristles as in many marine polychaetes. Or, they can occur as structured, but unconnected or loosely connected arrays, such as the mineral "teeth" in the radula of many Mollusca, the valves of chitons, the beak of a cephalopod, or the articulated exoskeletons of Arthropoda. Wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Philosophical Transactions Of The Royal Society B
''Philosophical Transactions of the Royal Society B: Biological Sciences'' is a biweekly peer-reviewed scientific journal published by the Royal Society. The editor-in-chief is Richard Dixon (UNT). Overview Each issue covers a specific area of the biological sciences. Each issue aims to create an original and authoritative synthesis, often bridging traditional disciplines, which showcases current developments and provides a foundation for future research, applications and policy decisions. Each issue is edited by one or more expert guest editors. The themes fall into one of four general categories: * Cell and Development * Health and Disease * Environment and Evolution * Neuroscience and Cognition All articles become freely accessible one year after their publication date. History ''Philosophical Transactions of the Royal Society'' was established in 1665 by the Royal Society and is the oldest scientific journal in the English-speaking world. Henry Oldenburg was appoint ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calcium Carbonate
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Materials containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is produced when calcium ions in hard water react with carbonate ions to form limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues. Chemistry Calcium carbonate shares the typical properties of other carbonates. Notably, it: *reacts with acids, releasing carbonic acid which quickly disintegrates into carbon dioxide and water: : *releases carbon dioxide upon heating, called a thermal decomposition reaction, or calcination (to above 840 °C in the case of ), t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobite
Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, existing in oceans for almost 270million years, with over 22,000 species having been described. Because trilobites had wide diversity and an easily fossilized mineralised exoskeleton made of calcite, they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy, paleontology, evolution, evolutionary biology, and plate tectonics. Trilobites are placed within the clade Artiopoda, which includes many organisms that are morphologically similar to trilobites, but are largely unmineralised. The relationship of Artiopoda to other arthropods is uncertain. Trilobites evolved into many ecological niches; some moved over the seabed as predators, scavengers, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambrian
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovician Period 486.85 Ma. Most of the continents lay in the southern hemisphere surrounded by the vast Panthalassa Ocean. The assembly of Gondwana during the Ediacaran and early Cambrian led to the development of new convergent plate boundaries and continental-margin arc magmatism along its margins that helped drive up global temperatures. Laurentia lay across the equator, separated from Gondwana by the opening Iapetus Ocean. The Cambrian marked a profound change in life on Earth; prior to the Period, the majority of living organisms were small, unicellular and poorly preserved. Complex, multicellular organisms gradually became more common during the Ediacaran, but it was not until the Cambrian that fossil diversity seems to rapidly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyolith
Hyoliths are animals with small conical shells, known from fossils from the Palaeozoic era. They are at least considered as being lophotrochozoan, and possibly being lophophorates, a group which includes the brachiopods (hyoliths may even be brachiopods themselves), while others consider them as being basal lophotrochozoans, or even molluscs. Morphology The shell of a hyolith is typically one to four centimeters in length, triangular or elliptical in cross section. Some species have rings or stripes. It comprises two parts: the main conical shell (previously referred to as a ‘conch’) and a cap-like operculum. Some also had two curved supports known as ''helens'' They are calcareous – probably aragonitic All of these structures grew by marginal accretion. Shell microstructure The orthothecid shell has an internal layer with a microstructure of transverse bundles, and an external layer comprising longitudinal bundles. Helens Some hyoliths had helens, long struc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain Mail
Mail (sometimes spelled maille and, since the 18th century, colloquially referred to as chain mail, chainmail or chain-mail) is a type of armour consisting of small metal rings linked together in a pattern to form a mesh. It was in common military use between the 3rd century BC and the 16th century AD in Europe, while it continued to be used militarily in Asia, Africa, and the Middle East as late as the 18th century. Even today it is still in use in industries such as Butcher, butchery and as protection against the powerful bites of creatures such as sharks. A coat of this armour is often called a hauberk or sometimes a byrnie. History The earliest examples of surviving mail were found in the Carpathian Basin at a burial in Horný Jatov, Slovakia dated in the 3rd century BC, and in a chieftain's burial located in Ciumești, Romania. Its invention is commonly credited to the Celts, [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pillbug
Armadillidiidae is a family of woodlice, a terrestrial crustacean group in the order Isopoda. Unlike members of some other woodlice families, members of this family can roll into a ball, an ability they share with the outwardly similar but unrelated pill millipedes and other animals. This ability gives woodlice in this family their common names of pill bugs or roly polies. Other common names include slaters, potato bugs, curly bugs, butchy boys, and doodle bugs. Most species are native to the Mediterranean Basin, while a few species have wider European distributions. The best-known species, ''Armadillidium vulgare'', was introduced to New England in the early 19th century and has become widespread throughout North America. Common names Ecology and behavior Pill bugs in the family Armadillidiidae are able to form their bodies into a ball shape, in a process known as '' conglobation''. Conglobation has evolved independently in several families; this behaviour is shared with p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
