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Elasmobranchii
Elasmobranchii
Elasmobranchii
(/ɪˌlæzməˈbræŋkiaɪ/[8]) is a subclass of Chondrichthyes
Chondrichthyes
or cartilaginous fish, including the sharks (superorder Selachii) and the rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm
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Precambrian
The Precambrian
Precambrian
(or Pre-Cambrian, sometimes abbreviated pЄ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic
Phanerozoic
Eon. The Precambrian
Precambrian
is so named because it preceded the Cambrian, the first period of the Phanerozoic
Phanerozoic
eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian
Precambrian
accounts for 88% of the Earth's geologic time. The Precambrian
Precambrian
(colored green in the timeline figure) is an informal unit of geologic time,[1] subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale
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Placoid Scale
The skin of most fishes is covered with scales, which, in many cases, are animal reflectors or produce animal coloration. Scales vary enormously in size, shape, structure, and extent, ranging from strong and rigid armour plates in fishes such as shrimpfishes and boxfishes, to microscopic or absent in fishes such as eels and anglerfishes. The morphology of a scale can be used to identify the species of fish it came from. Cartilaginous fishes (sharks and rays) are covered with placoid scales. Most bony fishes are covered with the cycloid scales of salmon and carp, or the ctenoid scales of perch, or the ganoid scales of sturgeons and gars
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Cambrian
The Cambrian
Cambrian
Period ( /ˈkæmbriən/ or /ˈkeɪmbriən/) was the first geological period of the Paleozoic
Paleozoic
Era, and of the Phanerozoic Eon.[6] The Cambrian
Cambrian
lasted 55.6 million years from the end of the preceding Ediacaran
Ediacaran
Period 541 million years ago (mya) to the beginning of the Ordovician
Ordovician
Period 485.4 mya.[7] Its subdivisions, and its base, are somewhat in flux
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Vulnerable Species
A vulnerable species is one which has been categorized by the International Union for Conservation of Nature
International Union for Conservation of Nature
as likely to become endangered unless the circumstances that are threatening its survival and reproduction improve. Vulnerability is mainly caused by habitat loss or destruction of the species home. Vulnerable habitat or species are monitored and can become increasingly threatened
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Overfishing
Overfishing
Overfishing
is a form of overexploitation where fish stocks are reduced to below acceptable levels. Overfishing
Overfishing
can occur in water bodies of any sizes, such as ponds, rivers, lakes or oceans, and can result in resource depletion, reduced biological growth rates and low biomass levels. Sustained overfishing can lead to critical depensation, where the fish population is no longer able to sustain itself. Some forms of overfishing, for example the overfishing of sharks, has led to the upset of entire marine ecosystems.[1] The ability of a fishery to recover from overfishing depends on whether the ecosystem's conditions are suitable for the recovery. Dramatic changes in species composition can result in an ecosystem shift, where other equilibrium energy flows involve species compositions different from those that had been present before the depletion of the original fish stock
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Michael Benton
Michael James "Mike" Benton[5] FRS[3] (born 8 April 1956) is a British palaeontologist, and professor of vertebrate palaeontology in the School of Earth Sciences at the University of Bristol.[6] His published work has mostly concentrated on the evolution of Triassic reptiles but he has also worked on extinction events and faunal changes in the fossil record.[4][7][8]Contents1 Education 2 Research 3 Awards and honours 4 Publications 5 References 6 External linksEducation[edit] Benton was educated at the University of Aberdeen
University of Aberdeen
and Newcastle University where he was awarded a PhD in 1981. Research[edit] Benton's research investigates palaeobiology, palaeontology, and macroevolution.[4][9][10] Benton is the author of several palaeontology text books (e.g
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Class (biology)
In biological classification, class (Latin: classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank.[a] Other well-known ranks in descending order of size are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order. Contents1 Definition 2 Hierarchy of ranks below and above the level of class 3 See also 4 Notes 5 ReferencesDefinition[edit] The class as a distinct rank of biological classification having its own distinctive name (and not just called a top-level genus (genus summum)) was first introduced by the French botanist Joseph Pitton de Tournefort in his classification of plants that appeared in his Eléments de botanique, 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct grade of organization -- i.e
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Gill
A gill (/ɡɪl/ ( listen)) is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a large surface area to the external environment. Branchia (pl. branchiae) is the zoologists' name for gills. With the exception of some aquatic insects, the filaments and lamellae (folds) contain blood or coelomic fluid, from which gases are exchanged through the thin walls. The blood carries oxygen to other parts of the body. Carbon dioxide
Carbon dioxide
passes from the blood through the thin gill tissue into the water. Gills or gill-like organs, located in different parts of the body, are found in various groups of aquatic animals, including mollusks, crustaceans, insects, fish, and amphibians
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Dorsal Fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates such as fishes, cetaceans (whales, dolphins, and porpoises), and the (extinct) ichthyosaur. Most species have only one dorsal fin, but some have two or three. Wildlife biologists often use the distinctive nicks and wear patterns which develop on the dorsal fins of large cetaceans to identify individuals in the field. The bony or cartilaginous bones that support the base of the dorsal fin in fish are called pterygiophores.Contents1 Functions 2 Structure 3 See also 4 NotesFunctions[edit] The main purpose of the dorsal fin is to stabilize the animal against rolling and to assist in sudden turns. Some species have further adapted their dorsal fins to other uses. The sunfish uses the dorsal fin (and the anal fin) for propulsion. In anglerfish, the anterior of the dorsal fin is modified into a biological equivalent to a fishing pole and a lure known as illicium or esca
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Clade
A clade (from Ancient Greek: κλάδος, klados, "branch"), also known as monophyletic group, is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single "branch" on the "tree of life".[1] The common ancestor may be an individual, a population, a species (extinct or extant), and so on right up to a kingdom and further. Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms.[2] Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic
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Shark Liver Oil
Shark
Shark
liver oil is an oil obtained from the livers of sharks. It has been used for centuries as a folk remedy to promote the healing of wounds and as a remedy for respiratory tract and digestive system problems.[5][6] It is still promoted as a dietary supplement, and additional claims have been made that it can treat other maladies such as cancer, HIV, radiation illness, swine flu and the common cold.[5][7] To date, none of these claims has been medically validated and shark liver oil (alone) is not a medication prescribed or utilized by American physicians.[7] However, it is a component of some moisturizing skin lotions,[6] and some hemorrhoid medications.[8][9]Contents1 Function in the Shark 2 Composition 3 Medicinal use 4 Shark
Shark
oil barometers 5 ReferencesFunction in the Shark[edit] Many fish maintain buoyancy with swim bladders
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Clasper
In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating.A close up ventral view of a chimaera clasper (Hydrolagus collie). Note the many small tooth-like projections covering the exterior surface. Male
Male
cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve as intromittent organs used to channel semen into the female's cloaca during mating. The act of mating in some fish including sharks usually includes one of the claspers raised to allow water into the siphon through a specific orifice. The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position
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Order (biology)
In biological classification, the order (Latin: ordo) isa taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family. An immediately higher rank, superorder, may be added directly above order, while suborder would be a lower rank. a taxonomic unit, a taxon, in that rank. In that case the plural is orders (Latin ordines). Example: All owls belong to the order Strigiformes What does and does not belong to each order is determined by a taxonomist, as is whether a particular order should be recognized at all. Often there is no exact agreement, with different taxonomists each taking a different position. There are no hard rules that a taxonomist needs to follow in describing or recognizing an order
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Adaptive Radiation
In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches.[1][2] Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits
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Swim Bladders
The swim bladder, gas bladder, fish maw or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish[1]) to control their buoyancy, and thus to stay at their current water depth without having to waste energy in swimming.[2] Also, the dorsal position of the swim bladder means the center of mass is below the center of volume, allowing it to act as a stabilizing agent. Additionally, the swim bladder functions as a resonating chamber, to produce or receive sound. The swim bladder is evolutionarily homologous to the lungs
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