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El Paso Group
The El Paso Formation is a geologic formation that is exposed from the Permian Basin of New Mexico and Texas to southeastern Arizona. It preserves fossils dating back to the Ordovician period. Description The formation is composed of gray cherty dolomite, limestone, and smaller amounts of siltstone. The formation often has a mottled appearance. Total thickness is . It lies unconformably on the Bliss Formation, the Coronado Sandstone, or (in the Florida Mountains) Precambrian basement, and is overlain by the Montoya Group or Portal Formation. Fossils The formation is only sparsely fossiliferous, but contains fossils of echinoderms, gastropods, trilobites, sponge spicules, and ''Nuia''. Rare ostracods, cephalopods, and brachiopods are also found, as is the trace fossil ''Planolites''. Bioherms up to high are found in the McKelligon Member, built up of siliceous sponges and receptaculitid '' Calathium''. History of investigation The formation was first named by George Burr Ri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Formation (stratigraphy)
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exposed in a geographical region (the stratigraphic column). It is the fundamental unit of lithostratigraphy, the study of strata or rock layers. A formation must be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by the thickness (geology), thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of a geologic formation goes back to the beginnings of modern scientific geology. The term was used by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Period (geology)
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (scientific branch of geology that aims to determine the age of rocks). It is used primarily by Earth scientists (including geologists, paleontologists, geophysicists, geochemists, and paleoclimatologists) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardized international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Receptaculites
''Receptaculites'' is the name-bearing genus for an extinct group of conspicuous benthic marine genera, the receptaculitids (formally Receptaculitaceae or Receptaculitidae), that lived from the Early Ordovician through the Permian period, peaking in the Middle Ordovician. The group's phylogenetic origin has long been obscure, with some arguing that they were calcareous algae, probably of the order Dasycladales.Byrnes, J.G. 1968. Notes on the nature and environmental significance of the Receptaculitaceae. Lethaia, vol. 1, p. 368-381. Receptaculitids lived in warm, shallow seas, but consensus disagreeing. They have been described from all continents except Antarctica. In some areas they were important reef-formers, and they also occur as isolated specimens. ''Receptaculites'' and its relatives have a double-spiral, radiating pattern of rhombus-shaped plates supported by spindle-like objects called meroms. Fossils can usually be identified by the intersecting patterns of clockwise ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siliceous Sponge
The siliceous sponges form a major group of the phylum Porifera, consisting of classes Demospongiae and Hexactinellida. They are characterized by spicules made out of silicon dioxide, unlike calcareous sponges. Individual siliachoates (silica skeleton scaffolding) can be arranged tightly within the sponginocyte or crosshatched and fused together. Siliceous spicules come in two sizes called megascleres and microscleres. Systematics Most studies support the monophyly of siliceous sponges. The group, as a part of the phylum Porifera, has been named ''Silicispongia'' Schmidt, 1862 and ''Silicea'' Bowerbank, 1864. ''Silicarea'' is a proposed new phylum based on molecular studies of the phylum Porifera. It consists of the Poriferan classes Demospongiae and Hexactinellida. Some scientists believe that Porifera is polyphyletic/paraphyletic, and that some sponges, the Calcarea, are a separate phylum which was the first to diverge from the main line of kingdom Animalia. Silicarea is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bioherm
A reef knoll is a land-based landform that comprises an immense pile of calcareous material that accumulated on a previously existing ancient sea floor. At the time of its accumulation it may have had enough structure from organisms such as sponges to have been free-standing and to withstand the sea currents as material accumulated, and was likely an atoll. Another possibility is the remains of deep water coral. Such structures are thus often fossil-rich. A bioherm is a sedimentary rocky landform enclosed or surrounded by rock of different origin. A biostrome is a distinctly bedded or broadly lenticular sedimentary rocky landform. Krumbein defines these terms as types of stromatolites: "Distinctly bedded, widely extensive, blanketlike build-ups are biostromes. Nodular, biscuit-like, dome-shaped or columnar stromatolites are also referred to as bioherms". England Examples on the Derbyshire/Staffordshire border include Thorpe Cloud and Bunster Hill in southern Dovedale, and also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planolites
''Planolites'' is an ichnogenus found throughout the Ediacaran and the Phanerozoic that is made during the feeding process of worm-like animals. The traces are generally small, , unlined, and rarely branched, with fill that differs from the host rock. Distribution ''Planolites'' fossils have been found in Africa, Asia, Europe, Antarctica, and the Americas (though many more specimens have been found in North America). Ichnospecies Ichnospecies in ''Planolites'' include: *''P. annularis'' Walcott, 1890 *''P. annularius'' Walcott, 1890 *''P. ballandus'' Webby, 1970 *''P. beverleyensis'' Billings, 1862 *''P. incipiens'' (Billings, 1861) *''P. montanus'' Richter, 1937 *''P. reticulatus'' Alpert, 1975 *''P. serpens'' Webby, 1970 *''P. striatus'' ( Hall, 1852) *''P. terraenovae'' Fillion and Pickerill, 1990 *''P. virgatus'' (Hall, 1847) See also List of Ediacaran genera This is a list of all described Ediacaran genera, including the Ediacaran biota. It contains 227 genera. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brachiopod
Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major categories are traditionally recognized, articulate and inarticulate brachiopods. The word "articulate" is used to describe the tooth-and-groove structures of the valve-hinge which is present in the articulate group, and absent from the inarticulate group. This is the leading diagnostic skeletal feature, by which the two main groups can be readily distinguished as fossils. Articulate brachiopods have toothed hinges and simple, vertically-oriented opening and closing muscles. Conversely, inarticulate brachiopods have weak, untoothed hinges and a more complex system of vertical and oblique (diagonal) muscles used to keep the two valves aligned. In many brachiopods, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by ''Nautilus'' and ''Allonautilus''. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been ident ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ostracod
Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typically around in size, but varying from in the case of ''Gigantocypris''. Their bodies are flattened from side to side and protected by a bivalve-like, chitinous or calcareous valve or "shell". The hinge of the two valves is in the upper (dorsal) region of the body. Ostracods are grouped together based on gross morphology. While early work indicated the group may not be monophyletic and early molecular phylogeny was ambiguous on this front, recent combined analyses of molecular and morphological data found support for monophyly in analyses with broadest taxon sampling. Ecologically, marine ostracods can be part of the zooplankton or (most commonly) are part of the benthos, living on or inside the upper layer of the sea floor. While Myodoc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobite
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 stu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gastropod
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. There are many thousands of species of sea snails and slugs, as well as freshwater snails, freshwater limpets, and land snails and slugs. The class Gastropoda contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian. , 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without a fossil record. Gastropoda (previously known as univalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversified class in the phylum, with 65,000 to 80,000 living snail and slug species. The anatomy, behavior, feeding, and re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echinoderm
An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Adult echinoderms are found on the sea bed at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7,000 living species, making it the second-largest grouping of deuterostomes, after the chordates. Echinoderms are the largest entirely marine phylum. The first definitive echinoderms appeared near the start of the Cambrian. The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to reproduce asexually and regenerate tissue, organs, and limbs; in some cases, they can undergo complete regeneration from a single limb. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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