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Xenacanthida
Xenacanthida (or Xenacanthiformes) is an order or superorder of extinct shark-like chondrichthyans (cartilaginous fish) known from the Carboniferous to Triassic. They were native to freshwater, marginal marine and shallow marine habitats. Some xenacanths may have grown to lengths of . Most xenacanths died out at the end of the Permian in the End-Permian Mass Extinction, with only a few forms surviving into the Triassic. Description The foundation of the tooth is prolonged lingually with a circlet button and a basal tubercle on the oral and aboral surfaces individually. The family Xenacanthidae consists of five genera: ''Xenacanthus'', '' Triodus'', '' Plicatodus'', '' Mooreodontus'' and '' Wurdigneria''; all of these are distinguished by cross sections of the points, crown center, length of the median edge, type of vertical cristae, and microscopic anatomy. Xenacanths are divided into two groups based on dental characteristics. Group one has tricuspid crowns containing two sto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xenacanthus
''Xenacanthus'' (from Ancient Greek wikt:ξένος, ξένος, xénos, 'foreign, alien' + wikt:ἄκανθος, ἄκανθος, akanthos, 'spine') is an extinct genus of Xenacanthida, xenacanth cartilaginous fish. It lived in freshwater environments, and fossils of various species have been found worldwide. Description ''Xenacanthus'' is a relatively small member of its order. ''X. decheni'' reached about , ''X. meisenheimensis'' reached up to , ''X''. (''Expleuracanthus'') ''gaudryi'' reached . ''X. parallelus'' is one of the smallest xenacanths, males reached and females reached , both are fully grown. The dorsal fin was ribbonlike and ran the entire length of the back and round the tail, where it joined with the anal fin. This arrangement resembles that of modern conger eels, and ''Xenacanthus'' probably swam in a similar manner. A distinctive spine projected from the back of the head and gave the genus its name. The spike has even been speculated to have been venomous, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catadromous
Fish migration is animal migration, mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear. Fish migrations involve movements of school of fish, schools of fish on a scale and duration larger than those arising during normal daily activities. Some particular types of migration are ''anadromous'', in which adult fish live in the sea and migrate into fresh water to spawn (biology), spawn; and ''catadromous'', in which adult fish live in fresh water and migrate into salt water to spawn. Marine forage fish often make large migrations between their spawning, feeding and nursery grounds. Their movements are associated with ocean currents and with the availability of food in different area ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Filter Feeder
Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specialized filtering organ that sieves out and/or traps solids. Filter feeders can play an important role in condensing biomass and removing excess nutrients (such as nitrogen and phosphate) from the local waterbody, and are therefore considered water-cleaning ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms. Filter feeders can be sessile, planktonic, nektonic or even neustonic (in the case of the buoy barnacle) depending on the species and the niches they have evolved to occupy. Extant species that rely on such method of feeding encompass numerous phyla, including poriferans ( sponges), cnidarians (jellyfish, sea pens and corals), arthropods ( krill, mysids and barna ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saar–Nahe Basin
Saar–Nahe Basin is a molasse basin in southwest Germany. The basin is located south of the Hunsrück mountains between the rivers Nahe and the Saar. The aggregation of sediments in the basin started in the late Carboniferous and Early Permian as part of the Variscan orogeny The Variscan orogeny, or Hercynian orogeny, was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Varis .... See also * Saar-Nahe Hills Further reading * * * * * * * * * * * * * * * {{DEFAULTSORT:Saar-Nahe Basin Structural geology Sedimentology Geology of Germany Basins of Europe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apex Predator
An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic levels. Food chains are often far shorter on land, usually limited to being secondary consumers – for example, Gray wolf, wolves prey mostly upon large herbivores (primary consumers), which eat plants (primary producers). The apex predator concept is applied in wildlife management, conservation biology, conservation, and ecotourism. Apex predators have a long evolutionary history, dating at least to the Cambrian period when animals such as ''Anomalocaris'' and ''Timorebestia'' dominated the seas. Humans have for many centuries interacted with other apex predators including the wolf, Bird of prey, birds of prey, and cormorants to hunt game animals, birds, and fish respectively. More recently, humans have started interacting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acanthodians
Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes). They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and chimaeras. Acanthodians possess a mosaic of features shared with both osteichthyans (bony fish) and chondrichthyans (cartilaginous fish). In general body shape, they were similar to modern sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteians ( gars, bowfins). The popular name "spiny sharks" is because they were superficially shark-shaped, with a streamlined body, paired fins, a strongly upturned tail, and stout, largely immovable bony spines supporting all the fins except the tail—hence, "spiny sharks". However, acanthodians are not true sharks; their close relation to modern cartilaginous fish can lead them to be considered "stem-sharks". Acanthodians had a cartilaginous skeleton, but their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palaeonisciformes
The Palaeonisciformes, commonly known as "palaeoniscoids" (also spelled "paleoniscoid", or alternatively "paleoniscids") are an extinct grouping of primitive ray-finned fish (Actinopterygii), spanning from the Silurian/Devonian to the Cretaceous. They are generally considered paraphyletic, but their exact relationships to living ray-finned fish are uncertain. While some and perhaps most palaeoniscoids likely belong to the stem-group of Actinopteryii, it has been suggested that some may belong to the crown group, with some of these possibly related to Cladistia (containing bichirs) and/or Chondrostei (which contains sturgeons and paddlefish). Many palaeoniscoids share a conservative body shape and a similar arrangement of skull bones, though paleoniscoids as a whole exhibit considerable diversity in body shape. Historic background The systematics of fossil and extant fishes has puzzled ichthyologists since the time of Louis Agassiz, who first grouped all Palaeozoic ray-finned f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Temnospondyl
Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphibians—that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent. A few species continued into the Jurassic and Early Cretaceous periods, but all had gone extinct by the Late Cretaceous. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including freshwater, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ambush Predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture their prey via stealth, luring or by (typically instinctive) strategies utilizing an element of surprise. Unlike pursuit predators, who chase to capture prey using sheer speed or endurance, ambush predators avoid fatigue by staying in concealment, waiting patiently for the prey to get near, before launching a sudden overwhelming attack that quickly incapacitates and captures the prey. The ambush is often opportunistic, and may be set by hiding in a burrow, by camouflage, by aggressive mimicry, or by the use of a trap (e.g. a web). The predator then uses a combination of senses to detect and assess the prey, and to time the strike. Nocturnal ambush predators such as cats and snakes have vertical slit pupils helping them to judge the distance to prey in dim light. Different ambush predators use a variety of means to capture their prey, from the long sticky tongues of chameleons to the expand ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scyliorhinidae
Scyliorhinidae is a Family (biology), family of sharks, one of a few families whose members share the common name catsharks, belonging to the Order (biology), order Carcharhiniformes, the ground sharks. Although they are generally known as catsharks, some species can also be called dogfish due to previous naming. However, a dogfish may generally be distinguished from a catshark as catsharks lay eggs while dogfish have live young. Like most bottom feeders, catsharks feed on benthic invertebrates and smaller fish. They are not harmful to humans. The family is paraphyletic, containing several distinct lineages that do not form a monophyletic group. Genera Scyliorhinidae includes the following genera: * ''Cephaloscyllium'' Theodore Gill, T. N. Gill, 1862 * ''Poroderma'' Andrew Smith (zoologist), A. Smith, 1838 * ''Scyliorhinus'' Henri Marie Ducrotay de Blainville, Blainville, 1816 Anatomy and appearance Scyliorhinidae catsharks may be distinguished by their elongated, cat- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". Organisms living in this zone are called benthos and include microorganisms (e.g., bacteria and fungi) as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here, known as bottom dwellers, generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud. Description Oceans The benthic region of the ocean begins at the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bransonella
''Bransonella'' is an extinct genus of marine xenacanth which lived during the Paleozoic era. It is known only from teeth which are easily distinguished from related genera by ornamentation on the cusp shaped like an inverted "V" and fin spines Teeth attributed to this genus are small, no greater than 2 millimeters. This suggests a small body size likely not exceeding a meter in length. It has been suggested their lifestyle was similar to modern Catsharks. It was used to erect a new order along with '' Barbclabornia'' based on ornamentation. There are four species currently attributed to this genus. The first species described was ''B. tridentata'' in 1933, which was erroneously identified as a conodont. ''B. nebraskensis'' was described from the late Pennsylvanian of Nebraska and later recognized from the middle Mississippian to the early Permian of Kansas, the Urals, Poland, Belgium, Russia, and England. ''B. lingulata'' is known from Serpukhovian of Russia. ''B. tribula'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
