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Pteridiniidae
''Pteridinium'' is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota. Body plan The three-lobed body is generally flat such that only two lobes are visible. Each lobe consists of a number of parallel ribs extending back to the main axis where the three lobes come together. Even on well-preserved specimens, there is no sign of a mouth, anus, eyes, legs, antennae, or any other appendages or organs. The organism grew primarily by the addition of new units, probably at both ends, with the inflation of existing units contributing little to its growth. Ecology Specimens found in what is thought to be life positions indicate that the creature rested on — or possibly in — the sediment in shallow seas. No tracks are known that would seem to be consistent with a moving ''Pteridinium''. It is unclear whether it performed photosynthesis, or osmotically extracted nutrients from seawater. Occurrence Fossils are common in late Pre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pteridiniidae
''Pteridinium'' is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota. Body plan The three-lobed body is generally flat such that only two lobes are visible. Each lobe consists of a number of parallel ribs extending back to the main axis where the three lobes come together. Even on well-preserved specimens, there is no sign of a mouth, anus, eyes, legs, antennae, or any other appendages or organs. The organism grew primarily by the addition of new units, probably at both ends, with the inflation of existing units contributing little to its growth. Ecology Specimens found in what is thought to be life positions indicate that the creature rested on — or possibly in — the sediment in shallow seas. No tracks are known that would seem to be consistent with a moving ''Pteridinium''. It is unclear whether it performed photosynthesis, or osmotically extracted nutrients from seawater. Occurrence Fossils are common in late Pre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ediacaran
The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia. The Ediacaran Period's status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years. Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacaran biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at . The Ediacaran marks the first appearance of widespread multicellular fauna following the end of Snowball Earth glaciation events, the so-called Ediacaran biota, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Northwest Territories
The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. At a land area of approximately and a 2016 census population of 41,790, it is the second-largest and the most populous of the three territories in Northern Canada. Its estimated population as of 2022 is 45,605. Yellowknife is the capital, most populous community, and only city in the territory; its population was 19,569 as of the 2016 census. It became the territorial capital in 1967, following recommendations by the Carrothers Commission. The Northwest Territories, a portion of the old North-Western Territory, entered the Canadian Confederation on July 15, 1870. Since then, the territory has been divided four times to create new provinces and territories or enlarge existing ones. Its current borders date from April 1, 1999, when the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobozoa
''Trilobozoa'' (meaning "three-lobed animals") is a phylum of extinct mobile animals that were originally classified into the Cnidaria. The basic body plan of ''Trilobozoa'' is often a tri-radial or radial sphere-shaped form with lobes radiating from its centre. Fossils of trilobozoans are restricted to marine strata of the Late Ediacaran period. History and interpretations Originally, both Fedonkin and Runnegar presumed that there were 2-3 families within the Trilobozoa, those families being Albumaresidae Fedonkin, 1985 and Tribrachididae Runnegar, 1992. Although, affinities with the Conulariida were made because of the conulariids possessing similar three-fold symmetry. Mikhail Fedonkin later classified the Trilobozoa as a class of the Phylum Coelenterata. Most of the members of what is now the modern day classification for Trilobozoa were thought to have originally been free swimming Jellyfish. Tribrachidium was once interpreted as a Edrioasteroid Echinoderm, although wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glide Symmetry
In 2-dimensional geometry, a glide reflection (or transflection) is a symmetry operation that consists of a reflection over a line and then translation along that line, combined into a single operation. The intermediate step between reflection and translation can look different from the starting configuration, so objects with glide symmetry are in general, not symmetrical under reflection alone. In group theory, the ''glide plane'' is classified as a type of opposite isometry of the Euclidean plane. A single glide is represented as frieze group p11g. A glide reflection can be seen as a limiting rotoreflection, where the rotation becomes a translation. It can also be given a Schoenflies notation as S2∞, Coxeter notation as ˆž+,2+ and orbifold notation as ∞×. Description The combination of a reflection in a line and a translation in a perpendicular direction is a reflection in a parallel line. However, a glide reflection cannot be reduced like that. Thus the effect of a re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spriggina
''Spriggina'' is a genus of early bilaterian animals whose relationship to living animals is unclear. Fossils of ''Spriggina'' are known from the late Ediacaran period in what is now South Australia. ''Spriggina floundersi'' is the official fossil emblem of South Australia. It has been found nowhere else. The organism reached about in length and may have been predatory. Its bottom was covered with two rows of tough interlocking plates, while one row covered its top; its front few segments fused to form a "head." ''Spriggina'' affinity is currently unknown; it has been variously classified as an annelid worm, a rangeomorph-like frond, a variant of ''Charniodiscus'', a proarticulatan, or an arthropod perhaps related to the trilobites, or even an extinct phylum. Lack of known segmented legs or limbs, and glide reflection instead of symmetric segments, suggest an arthropod classification is unlikely despite some superficial resemblance. The genus ''Spriggina'' may have originally co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dickinsonia
''Dickinsonia'' is an extinct genus of basal animal that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine. The individual ''Dickinsonia'' typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth is consistent with a stem-group bilaterian affinity, though some have suggested that it belongs to the fungi, or even an "extinct kingdom". It lived during the late Ediacaran (part of Precambrian). The discovery of cholesterol molecules in fossils of ''Dickinsonia'' lends support to the idea that ''Dickinsonia'' was an animal. Description ''Dickinsonia'' fossils are known only in the form of imprints and casts in sandstone beds. The specimens found range from a few millimetres to about in length, and from a fraction of a millimetre to a few millimetres thick. They are nearly bilaterally symmetric, segmented, round or oval in outline, slightly expanded to one end (i.e. egg-shaped out ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cnidaria
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Cnidarians mostly have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both (hence they are trimorphic). Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming species of Cubozoa and Scyphozo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paradoxides
''Paradoxides'' is a genus of large to very large trilobite found throughout the world during the Middle Cambrian period. One record-breaking specimen of ''Paradoxides davidis'', described by John William Salter in 1863, is . The cephalon was semicircular with free cheeks ending in long, narrow, recurved spines. Eyes were crescent shaped providing an almost 360° view, but only in the horizontal plane. Its elongate thorax was composed of 19-21 segments and adorned with longish, recurved pleural spines. Its pygidium was comparatively small. ''Paradoxides'' is a characteristic Middle-Cambrian trilobite of the 'Atlantic' (Avalonian) fauna. Avalonian rocks were deposited near a small continent called Avalonia in the Paleozoic Iapetus Ocean. Avalonian beds are now in a narrow strip along the East Coast of North America, and in Europe. Description The exoskeleton of ''Paradoxides'' is large to very large, relatively flat, and about one and a half times longer than wide, with greate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobites
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period () and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described. By the time trilobites first appeared in the fossil record, they were already highly diversified and geographically dispersed. Because trilobites had wide diversity and an easily fossilized exoskeleton, they left an extensive fossil record. The stud ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambrian
The Cambrian Period ( ; sometimes symbolized C with bar, êž’) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago (mya) to the beginning of the Ordovician Period 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 Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed. Sedgwick identified the layer as part of his task, along with Roderick Murchison, to subdivide the large "Transition Series", although the two geologists disagreed for a while on the appropriate categorization. The Cambrian is unique in its unusually high proportion of sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University Of North Carolina At Chapel Hill
A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, the designation is reserved for colleges that have a graduate school. The word ''university'' is derived from the Latin ''universitas magistrorum et scholarium'', which roughly means "community of teachers and scholars". The first universities were created in Europe by Catholic Church monks. The University of Bologna (''Università di Bologna''), founded in 1088, is the first university in the sense of: *Being a high degree-awarding institute. *Having independence from the ecclesiastic schools, although conducted by both clergy and non-clergy. *Using the word ''universitas'' (which was coined at its foundation). *Issuing secular and non-secular degrees: grammar, rhetoric, logic, theology, canon law, notarial law.Hunt Janin: "The unive ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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