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Chordate
And see text A CHORDATE is an animal belonging to the phylum CHORDATA; chordates possess a notochord , a hollow dorsal nerve cord , pharyngeal slits , an endostyle , and a post-anal tail , for at least some period of their life cycle. Chordates are deuterostomes , as during the embryo development stage the anus forms before the mouth. They are also bilaterally symmetric coelomates with metameric segmentation and a circulatory system . In the case of vertebrate chordates, the notochord is usually replaced by a vertebral column during development. Taxonomically, the phylum includes the following subphyla: the Vertebrata , which includes fish , amphibians , reptiles , birds , and mammals ; the Tunicata , which includes salps and sea squirts ; and the Cephalochordata
Cephalochordata
, which include the lancelets . There are also additional extinct taxa such as the Vetulicolia
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Vertebral Column
The VERTEBRAL COLUMN, also known as the BACKBONE or SPINE, is part of the axial skeleton . The vertebral column is the defining characteristic of a vertebrate , in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bones —vertebrae separated by intervertebral discs . The vertebral column houses the spinal canal , a cavity that encloses and protects the spinal cord . There are about 50,000 species of animals that have a vertebral column. The human vertebral column is one of the most-studied examples
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Neogene
The NEOGENE ( /ˈniːəˌdʒiːn/ ) (informally UPPER TERTIARY or LATE TERTIARY) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago (Mya ) to the beginning of the present Quaternary Period 2.58 Mya. The Neogene
Neogene
is sub-divided into two epochs , the earlier Miocene
Miocene
and the later Pliocene
Pliocene
. Some geologists assert that the Neogene
Neogene
cannot be clearly delineated from the modern geological period, the Quaternary . During this period, mammals and birds continued to evolve into roughly modern forms, while other groups of life remained relatively unchanged. Early hominids , the ancestors of humans, appeared in Africa
Africa
near the end of the period
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Paleogene
The PALEOGENE ( /ˈpæliːədʒiːn/ or /ˈpeɪliːədʒiːn/ ; also spelled PALAEOGENE or PALæOGENE; informally LOWER TERTIARY) is a geologic period and system that spans 43 million years from the end of the Cretaceous
Cretaceous
Period 66 million years ago (Mya ) to the beginning of the Neogene
Neogene
Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic
Phanerozoic
Eon. The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event
Cretaceous–Paleogene extinction event
that ended the preceding Cretaceous
Cretaceous
Period
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Cretaceous
The CRETACEOUS ( /krɪˈteɪʃəs/ , kri-TAY-shəs ) is a geologic period and system that spans 79 million years from the end of the Jurassic
Jurassic
Period 145 million years ago (mya ) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era . The Cretaceous
Cretaceous
Period is usually abbreviated K, for its German translation Kreide (chalk). The Cretaceous
Cretaceous
was a period with a relatively warm climate , resulting in high eustatic sea levels that created numerous shallow inland seas . These oceans and seas were populated with now-extinct marine reptiles , ammonites and rudists , while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds , as well as flowering plants , appeared
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Spinal Cord
The SPINAL CORD is a long, thin, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column . The brain and spinal cord together make up the central nervous system (CNS). In humans , the spinal cord begins at the occipital bone where it passes through the foramen magnum , and meets and enters the spinal canal at the beginning of the cervical vertebrae . The spinal cord extends down to between the first and second lumbar vertebrae where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) in men and around 43 cm (17 in) long in women. Also, the spinal cord has a varying width, ranging from 13 mm (1⁄2 in) thick in the cervical and lumbar regions to 6.4 mm (1⁄4 in) thick in the thoracic area
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Taxonomy (biology)
TAXONOMY (from Ancient Greek τάξις (taxis ), meaning 'arrangement', and -νομία (-nomia), meaning 'method ') is the science of defining and naming groups of biological organisms on the basis of shared characteristics. Organisms are grouped together into taxa (singular: taxon) and these groups are given a taxonomic rank ; groups of a given rank can be aggregated to form a super-group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain , kingdom , phylum (division is sometimes used in botany in place of phylum), class , order , family , genus and species . The Swedish botanist Carl Linnaeus
Carl Linnaeus
is regarded as the father of taxonomy, as he developed a system known as Linnaean taxonomy for categorization of organisms and binomial nomenclature for naming organisms
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Coelom
The COELOM (/ˈsiːləm/ SEE-ləm , plural COELOMS or COELOMATA /siːˈloʊmətə/ see-LOH-mə-tə ) (from Greek : κοῖλος koîlos, hollow, cavity) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In developed animals , it is lined with a mesodermal epithelium . In other animals, such as molluscs , it remains undifferentiated. CONTENTS* 1 Structure * 1.1 Development * 1.2 Origins * 2 Function * 3 Coelomic fluid * 4 Classification in zoology * 4.1 Coelomates * 4.1.1 Coelomate
Coelomate
phyla * 4.2 Pseudocoelomates * 4.2.1 Pseudocoelomate phyla * 4.3 Acoelomates * 4.3.1 Acoelomate
Acoelomate
phyla * 5 See also * 6 References * 7 Further reading STRUCTUREDEVELOPMENT Coelom
Coelom
formation begins in the gastrula stage
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Bilateral Symmetry
SYMMETRY IN BIOLOGY is the balanced distribution of duplicate body parts or shapes within the body of an organism. In nature and biology, symmetry is always approximate: for example plant leaves, while considered symmetrical, rarely match up exactly when folded in half. Symmetry
Symmetry
creates a class of patterns in nature , where the near-repetition of the pattern element is by reflection or rotation. The body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical. A small minority, notably among the sponges , exhibit no symmetry (i.e., are asymmetric). CONTENTS* 1 Radial symmetry * 1.1 Special
Special
forms of radial symmetry * 2 Spherical symmetry * 3 Bilateral symmetry * 4 Biradial symmetry * 5 Asymmetry * 6 References * 7 Sources RADIAL SYMMETRY These sea anemones have been painted to emphasize their radial symmetry
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Tail
The TAIL is the section at the rear end of an animal 's body; in general, the term refers to a distinct, flexible appendage to the torso . It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals , reptiles , and birds . While tails are primarily a feature of vertebrates , some invertebrates including scorpions and springtails , as well as snails and slugs , have tail-like appendages that are sometimes referred to as tails. Tailed objects are sometimes referred to as "caudate" and the part of the body associated with or proximal to the tail are given the adjective "caudal". CONTENTS * 1 Function * 2 Human tails * 3 Gallery * 4 See also * 5 References * 6 External links FUNCTION Vulpes lagopus (Arctic fox) sleeping with its tail wrapped as a blanket. Animal tails are used in a variety of ways. They provide a source of locomotion for fish and some other forms of marine life
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Palaeospondylus
PALAEOSPONDYLUS GUNNI ("Gunn's Ancient Vertebrae") is a mysterious, fish -like fossil vertebrate . Its fossils are described from Achannaras slate quarry in Caithness, Scotland
Scotland
. The fossil as preserved is carbonized, and indicates an eel -shaped animal of up to 6 centimetres (2 in) in length. The skull, which must have consisted of hardened cartilage, exhibits pairs of nasal and auditory capsules, with a gill-apparatus below its hinder part, but no indications of ordinary jaws. The phylogeny of this bizarre fossil has puzzled scientists since its discovery in 1890, and many taxonomies have been suggested. In 2004, researchers proposed that Palaeospondylus
Palaeospondylus
was a larval lungfish. Previously it had been classified as a larval tetrapod , unarmored placoderm , an agnathan , and a chimera
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Jurassic
The JURASSIC ( /dʒʊˈræsɪk/ ; from Jura Mountains
Jura Mountains
) was a geologic period and system that spanned 56 million years from the end of the Triassic
Triassic
Period 201.3 million years ago (Mya ) to the beginning of the Cretaceous
Cretaceous
Period 145 Mya. The Jurassic
Jurassic
constituted the middle period of the Mesozoic Era , also known as the Age of Reptiles. The start of the period was marked by the major Triassic–Jurassic extinction event . Two other extinction events occurred during the period: the Pliensbachian/ Toarcian event in the Early Jurassic, and the Tithonian event at the end; however, neither event ranks among the "Big Five" mass extinctions
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Ernst Haeckel
ERNST HEINRICH PHILIPP AUGUST HAECKEL (German: ; 16 February 1834 – 9 August 1919 ) was a German biologist , naturalist , philosopher, physician, professor, marine biologist, and artist who discovered, described and named thousands of new species , mapped a genealogical tree relating all life forms, and coined many terms in biology , including anthropogeny , ecology , phylum , phylogeny , stem cell , and Protista
Protista
. Haeckel promoted and popularised Charles Darwin
Charles Darwin
's work in Germany and developed the influential but no longer widely held recapitulation theory ("ontogeny recapitulates phylogeny") claiming that an individual organism's biological development, or ontogeny , parallels and summarises its species' evolutionary development, or phylogeny
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Cambrian
The CAMBRIAN Period ( /ˈkæmbriən/ or /ˈkeɪmbriən/ ) was the first geological period of the Paleozoic Era, of the Phanerozoic
Phanerozoic
Eon. 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. Its subdivisions, and its base, are somewhat in flux. The period was established (as “Cambrian series”) by Adam Sedgwick , who named it after Cambria , the Latinised form of Cymru, the Welsh name for Wales
Wales
, where Britain's Cambrian
Cambrian
rocks are best exposed
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Megaannum
A YEAR is the orbital period of the Earth
Earth
moving in its orbit around the Sun
Sun
. Due to the Earth's axial tilt , the course of a year sees the passing of the seasons , marked by changes in weather , the hours of daylight , and, consequently, vegetation and soil fertility . In temperate and subpolar regions around the planet, four seasons are generally recognized: spring , summer , autumn and winter . In tropical and subtropical regions several geographical sectors do not present defined seasons; but in the seasonal tropics , the annual wet and dry seasons are recognized and tracked. The current year is 2018. A calendar year is an approximation of the number of days of the Earth's orbital period as counted in a given calendar . The Gregorian, or modern, calendar , presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars ; see below
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Triassic
The TRIASSIC ( /traɪˈæsɪk/ ) is a geologic period and system which spans 50.9 million years from the end of the Permian
Permian
Period 251.902 million years ago (Mya ), to the beginning of the Jurassic Period 201.3 Mya . The Triassic
Triassic
is the first period of the Mesozoic Era . Both the start and end of the period are marked by major extinction events . The Triassic
Triassic
began in the wake of the Permian– Triassic
Triassic
extinction event , which left the earth's biosphere impoverished; it would take well into the middle of this period for life to recover its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs , first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic
Jurassic
Period
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