|
Helicoplacus
''Helicoplacus'' (often misspelled ''Helioplacus'') is the earliest well-studied fossil echinoderm. Fossil plates are known from several regions. Complete specimens were found in Lower Cambrian strata of the White Mountains of California. The animal was a cigar-shaped creature up to long that stood upright on one end. Unlike more typical echinoderms such as sea stars, ''Helicoplacus'' does not have fivefold symmetry. Instead, there is a spiral food groove on the outside along which food was moved to a mouth that is thought to be on the side. The respiratory system appears to be primitive. Although the animal does not look like a typical echinoderm, the plates are composed of the characteristic calcareous plates known as '' stereom'' that are common to all echinoderms. The ambulacrum is similar to that of the Edrioasteroidea; as a result, ''Helicoplacus'' may belong to Pelmatozoa. Other contemporaneous echinoderms are known to have existed from their dissociated plates, but other ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicoplacoidea
Helicoplacoidea is an extinct class within the Echinodermata. All known taxa were discovered in sediments dating back to the Cambrian.Fossilworks: Helicoplacoidea ''fossilworks.org''. Retrieved 2021-01-13. Description Helicoplacoid skeletons consist of small platelets arranged like those of , lacking fused skeletons as inechinoids
Sea urchins () are spine (zoology), spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every dept ...
[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Echinodermata Orders
This List of echinoderm orders concerns the various classes and orders into which taxonomists categorize the roughly 7000 extant species as well as the extinct species of the exclusively marine phylum Echinodermata. Subphylum Crinozoa Class Crinoidea * Subclass Articulata (540 species) ** Order Bourgueticrinida ** Order Comatulida ** Order Cyrtocrinida ** Order Hyocrinida ** Order Isocrinida ** Order Millericrinida * Subclass †Flexibilia * Subclass † Camerata * Subclass †Disparida Image:Comaster schlegelii.JPG, ''Comaster schlegelii'' (Comatulida) Image:Holopus 2.jpg, ''Holopus sp.'' (Cyrtocrinida) Image:Encrinus liliiformis 4.JPG, '' Encrinus liliiformis'' ( Encrinida) Image:Calamocrinus diomedæ (Plate XXVIII) BHL4232451.jpg, '' Calamocrinus diomedae'' (Hyocrinida) Image:Proisocrinus ruberrimus.jpg, ''Proisocrinus ruberrimus'' (Isocrinida) Image:Liliocrinus polydactylus MHNT.jpg, '' Liliocrinus polydactylus'' (Millericrinida) Class Paracrinoidea † No or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Prehistoric Echinoderms
This list of prehistoric echinoderms is an attempt to create a comprehensive listing of all genera that have ever been included in the Echinoderms that have been preserved as fossils. This list excludes purely vernacular terms. It includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (''nomina dubia''), or were not formally published (''nomina nuda''), as well as junior synonyms of more established names, and genera that are no longer considered echinoderms. The list includes thousands of genera. *Extinct genera are marked with a dagger ( †). *Extant genera are bolded. Naming conventions and terminology Naming conventions and terminology follow the International Code of Zoological Nomenclature. Technical terms used include: * Junior synonym: A name which describes the same taxon as a previously published name. If two or more genera are formally designated and the type specimens are later assigned to the same genus, the first to be pub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Early Cambrian
The Cambrian Period ( ; sometimes symbolized Ꞓ) 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 Cambrian bi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stem Group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade, a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as a crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants. The concept was developed by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen. Contents of the crown gr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cambrian Echinoderms
The Cambrian Period ( ; sometimes symbolized Ꞓ) 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 Cambrian bio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prehistoric Echinozoa Genera
Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of symbols, marks, and images appears very early among humans, but the earliest known writing systems appeared 5000 years ago. It took thousands of years for writing systems to be widely adopted, with writing spreading to almost all cultures by the 19th century. The end of prehistory therefore came at very different times in different places, and the term is less often used in discussing societies where prehistory ended relatively recently. In the early Bronze Age, Sumer in Mesopotamia, the Indus Valley Civilisation, and ancient Egypt were the first civilizations to develop their own scripts and to keep historical records, with their neighbors following. Most other civilizations reached the end of prehistory during the following Iron Age. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicocystis
''Helicocystis'' is a stalked, spiralling pentaradial echinoderm known from the Cambrian Jbel Wawrmast Formation JBEL may refer to: * A variation on the name Jabal * ''Journal of Business, Entrepreneurship and the Law'' (JBEL), a publication of Pepperdine University School of Law See also * * Jabal (other) Jabal, Jabel, Jebel or Jibal may refer t .... References Prehistoric echinoderm genera Helicoplacoidea {{Paleo-echinoderm-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, . ''Magnesian limestone'' is an obsolete and poorly-defined term used variously for dolomite, for limes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions. Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.Blatt, Harvey and Robert J. Tracy (1996) ''Petrology: Igneous, Sedimentary and Metamorphic'', 2nd ed., Freeman, pp. 281–292 Shale is characterized by its tendency to split into thin layers ( laminae) less than one centimeter in thickness. This property is called '' fissility''. Shale is the most common sedimentary rock. The term ''shale'' is sometimes applied more broadly, as essentially a synonym for mudrock, rather than in the more narrow sense of clay-rich fissile mudrock. Texture Shale typically exhibits varying degrees of fissility. Because of the parallel orientation of clay mineral flakes in shale, it breaks into thin layers, often splintery and usually parallel to the otherwise indistinguishable beddin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arkarua
''Arkarua adami'' is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of five small dots from the middle of the disk center. Fossils range from 3 to 10 mm in diameter. ''Arkarua'' is known only from the Ediacaran beds of the Flinders Ranges in South Australia. The generic name refers to Arkaroo, a giant snake from the Dreaming of the local Aboriginal people. Classification All known specimens of ''Arkarua'' are casts that give no clue to the internal structure, making classification problematic. Because of ''Arkaruas pentamerous symmetry, it is tentatively placed within phylum Echinodermata. Because of its flattened disk- or button-shape, coupled with its pentamerous symmetry, some claim that it can be further classified into the Edrioasteroidea, a class of the echinoderms. This identification remains suspect, as the fossils do not appear to have either madrep ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.jpg "Click for more on -> List Of Prehistoric Echinoderms")
Saunders_Quarry-1.jpg "Click for more on -> Sandstone")
