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Heterastridium
''Heterastridium'' is an extinct genus of marine hydrozoan. It is the only accepted genus in the monotypic family Heterastridiidae. The fossils date from the Upper Triassic. They are mostly discoid or spherical and some forms found in the Karakorum mountains are called Karakorum stones.Erik Flügel (1960) Heterastridium conglobatum conglobatum Reuss, an Upper Triassic Hydrozoan from the Petra-Tou-Roumiou Limestone of Pendakomo, Cyprus. Journal of Paleontology 34(1):127-132 They vary in diameter from 1 to 35 cm and appear to follow Cope's rule Cope's rule, named after American paleontologist Edward Drinker Cope, postulates that population lineages tend to increase in body size over evolutionary time. It was never actually stated by Cope, although he favoured the occurrence of linear e ... for the prehistoric climate. References Anthoathecata Prehistoric cnidarian genera {{paleo-anthoathecata-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus. :E.g. '' Panthera leo'' (lion) and '' Panthera onca'' (jaguar) are two species within the genus ''Panthera''. ''Panthera'' is a genus within the family Felidae. The composition of a genus is determined by taxonomists. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful: # monophyly – all descendants of an ancestral taxon are grouped together (i.e. phylogenetic analysis should c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrozoa
Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in freshwater habitats. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria. Some examples of hydrozoans are the freshwater jelly ('' Craspedacusta sowerbyi''), freshwater polyps (''Hydra''), '' Obelia'', Portuguese man o' war (''Physalia physalis''), chondrophores (Porpitidae), " air fern" (''Sertularia argentea''), and pink-hearted hydroids ('' Tubularia''). Anatomy Most hydrozoan species include both a polypoid and a medusoid stage in their lifecycles, although a number of them have only one or the other. For example, ''Hydra'' has no medusoid stage, while '' Liriope'' lacks the polypoid stage. Polyps The hydro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. The Triassic Period is subdivided into three epochs: Early Triassic, Middle Triassic and Late Triassic. The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished; it was well into the middle of the Triassic before life recovered its former diversity. Three categories of organisms can be distinguished in the Triassic record: survivors from the extinction event, new groups that flourished briefly, and other new groups that went on to dominate the Mesozoic Era. Reptiles, especially archosaurs, were the chief terrestrial vertebrates during this time. A specialized subgroup of arch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Karakorum
Karakorum ( Khalkha Mongolian: Хархорум, ''Kharkhorum''; Mongolian Script:, ''Qaraqorum''; ) was the capital of the Mongol Empire between 1235 and 1260 and of the Northern Yuan dynasty in the 14–15th centuries. Its ruins lie in the northwestern corner of the Övörkhangai Province of modern-day Mongolia, near today's town of Kharkhorin and adjacent to the Erdene Zuu Monastery, the probably earliest surviving Buddhist monastery in Mongolia. They are part of the upper part of the World Heritage Site Orkhon Valley. History Foundation of empires The Orkhon valley was a center of the Xiongnu, Göktürk, and Uyghur empires. To the Göktürks, the nearby Khangai Mountains had been the location of the Ötüken (the locus of power), and the Uyghur capital Karabalgasun was located close to where later Karakorum would be erected (downstream the Orkhon River 27 km north–west from Karakorum). This area is probably also one of the oldest farming areas in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cope's Rule
Cope's rule, named after American paleontologist Edward Drinker Cope, postulates that population lineages tend to increase in body size over evolutionary time. It was never actually stated by Cope, although he favoured the occurrence of linear evolutionary trends. It is sometimes also known as the Cope–Depéret rule, because Charles Depéret explicitly advocated the idea. Theodor Eimer had also done so earlier. The term "Cope's rule" was apparently coined by Bernhard Rensch, based on the fact that Depéret had "lionized Cope" in his book. While the rule has been demonstrated in many instances, it does not hold true at all taxonomic levels, or in all clades. Larger body size is associated with increased fitness for a number of reasons, although there are also some disadvantages both on an individual and on a clade level: clades comprising larger individuals are more prone to extinction, which may act to limit the maximum size of organisms. Function Effects of growth Direct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anthoathecata
Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed, and spectacular group. It has also been called Gymnoblastea and (with or without an emended ending ''-ae''), Anthomedusa, Athecata, Hydromedusa, and Stylasterina. There are about 1,200 species worldwide.Schuchert, P. (2014). Anthoathecata. Accessed through: Schuchert, P. (2014) World Hydrozoa database at http://www.marinespecies.org/hydrozoa/aphia.php?p=taxdetails&id=13551 on 2014-10-31 These hydrozoans always have a polyp stage. Their hydranths grow either solitary or in colonies. There is no firm perisarc around the polyp body. The medusae, or jellyfish, are solitary animals, with tentacles arising from the bell margin, lacking statocysts but possessing radial canals. Their gonads are on the manubrium ("handle").Bouillon, J.; Gravili, C.; Pagès, F.; Gili, J.-M.; Boero, F. (2006). An in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
