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Craniata
A craniate is a member of the Craniata (sometimes called the Craniota), a proposed clade of chordate animals with a skull of hard bone or cartilage. Living representatives are the Myxini
Myxini
(hagfishes), Hyperoartia
Hyperoartia
(including lampreys), and the much more numerous Gnathostomata
Gnathostomata
(jawed vertebrates).[2][3] The clade was conceived largely on the basis of the Hyperoartia (lampreys and kin) being more closely related to the Gnathostomata (jawed vertebrates) than the Myxini
Myxini
(hagfishes)
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Class (biology)
In biological classification, class (Latin: classis) is:a taxonomic rank. 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. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the prefix sub-: subclass (Latin: subclassis). a taxonomic unit, a taxon, in that rank. In that case the plural is classes (Latin classes)Example: Dogs are in the class Mammalia.The composition of each class is determined by a taxonomist. Often there is no exact agreement, with different taxonomists taking different positions. There are no hard rules that a taxonomist needs to follow in describing a class, but for well-known animals there is likely to be consensus. In botany, classes are now rarely discussed
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Keratin
Keratin
Keratin
(/ˈkɛrətɪn/[1][2]) is one of a family of fibrous structural proteins. It is the key structural material making up hair, horns, claws, hooves, and the outer layer of human skin. Keratin
Keratin
is also the protein that protects epithelial cells from damage or stress. Keratin
Keratin
is extremely insoluble in water and organic solvents
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Skull
The skull is a bony structure that forms the head in most vertebrates. It supports the structures of the face and provides a protective cavity for the brain.[1] The skull is composed of two parts: the cranium and the mandible. In the human these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone. The skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth.[2] In humans these sensory structures are part of the facial skeleton. Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, and fixing the position of the ears to enable sound localisation of the direction and distance of sounds
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Bone
A bone is a rigid organ that constitutes part of the vertebrate skeleton. Bones support and protect the various organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have a complex internal and external structure. They are lightweight yet strong and hard, and serve multiple functions. Bone
Bone
tissue (osseous tissue) is a hard tissue, a type of dense connective tissue. It has a honeycomb-like matrix internally, which helps to give the bone rigidity. Bone
Bone
tissue is made up of different types of bone cells. Osteoblasts and osteocytes are involved in the formation and mineralization of bone; osteoclasts are involved in the resorption of bone tissue. Modified (flattened) osteoblasts become the lining cells that form a protective layer on the bone surface
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Cartilage
Cartilage
Cartilage
is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bones at the joints, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components. It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. Because of its rigidity, cartilage often serves the purpose of holding tubes open in the body
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Molecular Phylogenetics
Molecular phylogenetics (/məˈlɛkjʊlər ˌfaɪloʊdʒəˈnɛtɪks, mɒ-, moʊ-/[1][2]) is the branch of phylogeny that analyses hereditary molecular differences, mainly in DNA
DNA
sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree. Molecular phylogenetics is one aspect of molecular systematics, a broader term that also includes the use of molecular data in taxonomy and biogeography.Contents1 History 2 Techniques and applications 3 Theoretical background 4 Limitations of molecular systematics 5 See also 6 Notes and references 7 Further reading 8 External linksHistory[edit] Further information: History of molecular evolution The theoretical frameworks for molecular systematics were laid in the 1960s in the works of Emile Zuckerkandl, Emanuel Margoliash, Linus Pauling, and Walter M
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Monophyly
In cladistics, a monophyletic group is a group of organisms that forms a clade, which consists of all the descendants of a common ancestor. Monophyletic groups are typically characterised by shared derived characteristics (synapomorphies), which distinguish organisms in the clade from other organisms. The arrangement of the members of a monophyletic group is called a monophyly. Monophyly
Monophyly
is contrasted with paraphyly and polyphyly as shown in the second diagram. A paraphyletic group consists of all of the descendants of a common ancestor minus one or more monophyletic groups. A polyphyletic group is characterized by convergent features or habits of scientific interest (for example, night-active primates, fruit trees, aquatic insects). The features by which a polyphyletic group is differentiated from others are not inherited from a common ancestor. These definitions have taken some time to be accepted
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Placodermi
Antiarchi † Arthrodira † Brindabellaspida † Petalichthyida † Phyllolepida † Ptyctodontida † Rhenanida † Acanthothoraci † ?Pseudopetalichthyida † ?Stensioellida †Placodermi (from the Greek πλάξ = plate and δέρμα = skin, literally "plate-skinned") is an extinct class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian Period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches. Placoderms are paraphyletic, and consist of several distinct outgroups or sister taxa to all living jawed vertebrates, which originated among their ranks. This is illustrated by a 419-million-year-old fossil, Entelognathus, from China, which is the only known placoderm with a type of bony jaw like that found in modern bony fishes
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Lamprey
† = extinctMouth of a sea lamprey, Petromyzon
Petromyzon
marinusMicroscopic cross section through the pharynx of a larva from an unknown lamprey speciesLampreys (sometimes also called, inaccurately, lamprey eels) are any jawless fish of the order Petromyzontiformes, placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like sucking mouth
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Teleostomi
Teleostomi
Teleostomi
is an obsolete clade of jawed vertebrates that supposedly includes the tetrapods, bony fish, and the wholly extinct acanthodian fish. Key characters of this group include an operculum and a single pair of respiratory openings, features which were lost or modified in some later representatives. The teleostomes include all jawed vertebrates except the chondrichthyans and the extinct class Placodermi. Recent studies indicate that Osteichthyes
Osteichthyes
evolved from placoderms like Entelognathus, while acanthodians are more closely related to modern chondrichthyes
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Acanthodii
Climatiiformes Ischnacanthiformes Acanthodiformes Acanthodii
Acanthodii
or acanthodians (sometimes called spiny sharks) is a paraphyletic class of extinct teleostome fish, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans (gars, bowfins). They represent several independent phylogenetic branch of fishes leading to the still-extant Chondrichthyes.[1] The popular name "spiny sharks" is a partial misnomer for these early jawed fishes. The name was coined because they were superficially shark-shaped, with a streamlined body, paired fins, and a strongly upturned tail; stout, largely immovable bony spines supporting all the fins except the tail - hence, "spiny sharks"; in retrospect, however, their close relation to modern cartilaginous fish can lead them to be considered "stem-sharks"
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Temnospondyli
See belowTemnospondyli (from Greek τέμνειν (temnein, "to cut") and σπόνδυλος (spondylos, "vertebra")) is a diverse subclass of extinct small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Cretaceous. Fossils have been found on every continent. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including fresh water, 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
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Parareptiles
Parareptilia ("at the side of reptiles") is a subclass or clade of reptiles which is variously defined as an extinct group of primitive anapsids, or a more cladistically correct alternative to Anapsida. Whether the term is valid depends on the phylogenetic position of turtles, whose relationships to other reptilian groups are still uncertain. History of classification[edit] The name Parareptilia was coined by Olson in 1947 to refer to an extinct group of Paleozoic reptiles, as opposed to the rest of the reptiles or Eureptilia ("true reptiles").Life restoration of Nyctiphruretus acudensThe name fell into disuse until it was revived by cladistic studies, to refer to those anapsids that were thought to be unrelated to turtles. Gauthier et al
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Brain
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head, usually close to the sensory organs for senses such as vision. The brain is the most complex organ in a vertebrate's body. In a human, the cerebral cortex contains approximately 15–33 billion neurons,[1] each connected by synapses to several thousand other neurons. These neurons communicate with one another by means of long protoplasmic fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells. Physiologically, the function of the brain is to exert centralized control over the other organs of the body. The brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows rapid and coordinated responses to changes in the environment
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