A reef is a bar of rock, coral or similar material, lying beneath the surface of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, etc.—but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae. Artificial reefs sometimes have a role in enhancing the physical complexity of featureless sand bottoms, in order to attract a diverse assemblage of organisms algae and fish. Earth's largest reef system is the Great Barrier Reef in Australia, at a length of over 2,300 kilometres. There is a variety of biotic reef types, including oyster reefs and sponge reefs, but the most massive and distributed are tropical coral reefs. Although corals are major contributors to the framework and bulk material comprising a coral reef; these biotic reef types take on additional names depending upon how the reef lies in relation to the land, if any. Reef types include fringing reefs, barrier reefs, atolls.
A fringing reef is a reef, attached to an island. A barrier reef forms a calcareous barrier around an island resulting in a lagoon between the shore and the reef. An atoll is a ring reef with no land present; the reef front is a high energy locale whereas the internal lagoon will be at a lower energy with fine grained sediments. Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth's history. In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits. Corals, including some major extinct groups Rugosa and Tabulata, have been important reef builders through much of the Phanerozoic since the Ordovician Period. However, other organism groups, such as calcifying algae members of the red algae Rhodophyta, molluscs have created massive structures at various times.
During the Cambrian Period, the conical or tubular skeletons of Archaeocyatha, an extinct group of uncertain affinities, built reefs. Other groups, such as the Bryozoa have been important interstitial organisms, living between the framework builders; the corals which build reefs today, the Scleractinia, arose after the Permian–Triassic extinction event that wiped out the earlier rugose corals, became important reef builders throughout the Mesozoic Era. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of the scleractinian corals, whose skeletons are aragonite. However, there are some unusual examples of well-preserved aragonitic rugose corals in the late Permian. In addition, calcite has been reported in the initial post-larval calcification in a few scleractinian corals. Scleractinian corals may have arisen from a non-calcifying ancestor independent of the rugosan corals. One useful definition distinguishes reefs from mounds as follows: Both are considered to be varieties of organosedimentary buildups – sedimentary features, built by the interaction of organisms and their environment, that have synoptic relief and whose biotic composition differs from that found on and beneath the surrounding sea floor.
Reefs are held up by a macroscopic skeletal framework. Coral reefs are an example of this kind. Corals and calcareous algae grow on top of one another and form a three-dimensional framework, modified in various ways by other organisms and inorganic processes. By contrast, mounds lack a macroscopic skeletal framework. Mounds are built by organisms that don't grow a skeletal framework. A microbial mound might be built or by cyanobacteria. Examples of biostromes formed by cyanobacteria occur in the Great Salt Lake in Utah, in Shark Bay on the coast of Western Australia. Cyanobacteria do not have skeletons, individuals are microscopic. Cyanobacteria can encourage the precipitation or accumulation of calcium carbonate to produce distinct sediment bodies in composition that have relief on the seafloor. Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms, but they still exist today. Bryozoans and crinoids, common contributors to marine sediments during the Mississippian, for instance, produced a different kind of mound.
Bryozoans are small and the skeletons of crinoids disintegrate. However and crinoid meadows can persist over time and produce compositionally distinct bodies of sediment with depositional relief; the Proterozoic Belt Supergroup contains evidence of possible microbial mat and dome structures similar to stromatolite reef complexes. Benjamin Kahn Coral reef Reef Hobbyist Magazine Placer Pseudo-atoll Shears N. T. Biogeography, community structure and biological habitat types of subtidal reefs on the South Island West Coast, New Zealand. Science for Conservation 281. P 53. Department of Conservation, New Zealand. Reef Rescue - Smithsonian Ocean Portal Coral Reefs of the Tropics: facts and movies from The Nature Conservancy NOAA Photo Library Reef Environmental Education Foundation NOS Data Explorer - A portal to obtain NOAA National Ocean Service data Reef formation Atoll
Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organisms in the Tethys Ocean, until their complete extinction at the close of the Cretaceous. The Late Jurassic forms were elongate, with both valves being shaped pipe or stake-shaped, while the reef-building forms of the Cretaceous had one valve that became a flat lid, with the other valve becoming an inverted spike-like cone; the size of these conical forms ranged from just a few centimeters to well over a meter in length. Their "classic" morphology consisted of a lower conical valve, attached to the seafloor or to neighboring rudists, a smaller upper valve that served as a kind of lid for the organism; the small upper valve could take a variety of interesting forms, including: a simple flat lid, a low cone, a spiral, a star-shaped form. The oldest rudists are found in late Jurassic rocks in France.
The rudists became extinct at the end of the Cretaceous as a result of the Cretaceous–Paleogene extinction event. It had been thought that this group began a decline about 2.5 million years earlier which culminated in complete extinction half a million years before the end of the Cretaceous. The extinction of rudist bivalves was stepwise during the Maastrichtian; the rudists are, according to different systematic schemes, placed in the orders Hippuritida or Rudistes. Order: †Hippuritida Suborder: †Hippuritidina Superfamily: †Caprinoidea Family: †Antillocaprinidae Family: †Caprinidae Family: †Ichthyosarcolitidae Superfamily: †Radiolitoidea Family: †Caprotinidae Family: †Diceratidae Family: †Hippuritidae Family: †Plagioptychidae Family: †Polyconitidae Family: †Radiolitidae Suborder: †Requieniidina Superfamily: †Requienioidea Family: †RequieniidaeBieler, Carter & Coan in 2010 named the non-Hippuritid families Megalodontoidea and Chamoidea, of Megalodontida and Venerida as "Rudists", but this classification was not monophyletic.
The classification of rudists as true reef-builders is controversial because they would catch and trap lots of sediment between their lower conical valves. However, rudists were one of the most important constituents of reefs during the Cretaceous Period. During the Cretaceous, rudist reefs were so successful that they drove scleractinian corals out of many tropical environments, including shelves that are today the Caribbean and the Mediterranean, it is that their success as reef builders was at least due to the extreme environment of the Cretaceous. During this period tropical waters were between 6°C and 14°C warmer than today and more saline, while this may have been a suitable environment for the rudists, it was not nearly so hospitable to corals and other contemporary reef builders; these rudist reefs were sometimes hundreds of meters tall and ran for hundreds of kilometers on continental shelves. Because of their high porosity, rudist reefs are favored oil traps. Simon F. Mitchell. ""The oldest barnacle from the Caribbean is a rudist bivalve"".
Cretaceous Research. 26: 895–897. "An Introduction to the Paleontology of Rudist Bivalves". Retrieved 2 July 2006. "Rudist Reef at the Smithsonian Ocean Portal". "More about Rudists"
Caprinidae is a family of rudists, a group of unusual extinct saltwater clams, marine heterodont bivalves in the order Hippuritida. These stationary intermediate-level epifaunal suspension feeders lived in the Cretaceous period, from 140.2 to 66.043 Ma. The rudists became extinct at the end of the Cretaceous as a result of the Cretaceous–Paleogene extinction event. Fossils of this genus have been found in the sediments of Europe, Cuba, Guatemala, Japan, Oman, the Philippines, Russia, the United States and Venezuela. †Antillocaprina †Caprina †Caprinula †Caprinuloidea †Coalcomana †Conchemipora †Guzzyella †Huetamia †Jalpania †Mathesia †Mexicaprina †Muellerriedia †Neocaprina †Offneria †Orthoptychus †Pachytraga †Pacificaprina †Pantojaloria †Texicaprina †Titanosarcolites
The Triassic is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago, to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished. 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 Period; the first true mammals, themselves a specialized subgroup of therapsids evolved during this period, as well as the first flying vertebrates, the pterosaurs, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to rift into two separate landmasses, Laurasia to the north and Gondwana to the south.
The global climate during the Triassic was hot and dry, with deserts spanning much of Pangaea's interior. However, the climate became more humid as Pangaea began to drift apart; the end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias"; the Triassic is separated into Early and Late Triassic Epochs, the corresponding rocks are referred to as Lower, Middle, or Upper Triassic. The faunal stages from the youngest to oldest are: During the Triassic all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator and spanning from pole to pole, called Pangaea.
From the east, along the equator, the Tethys sea penetrated Pangaea, causing the Paleo-Tethys Ocean to be closed. In the mid-Triassic a similar sea penetrated along the equator from the west; the remaining shores were surrounded by the world-ocean known as Panthalassa. All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates; the supercontinent Pangaea was rifting during the Triassic—especially late in that period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangaea, which separated New Jersey from Morocco, are of Late Triassic age. S. these thick sediments comprise the Newark Group. Because a super-continental mass has less shoreline compared to one broken up, Triassic marine deposits are globally rare, despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west, thus Triassic stratigraphy is based on organisms that lived in lagoons and hypersaline environments, such as Estheria crustaceans.
At the beginning of the Mesozoic Era, Africa was joined with Earth's other continents in Pangaea. Africa shared the supercontinent's uniform fauna, dominated by theropods and primitive ornithischians by the close of the Triassic period. Late Triassic fossils are more common in the south than north; the time boundary separating the Permian and Triassic marks the advent of an extinction event with global impact, although African strata from this time period have not been studied. During the Triassic peneplains are thought to have formed in what is now southern Sweden. Remnants of this peneplain can be traced as a tilted summit accordance in the Swedish West Coast. In northern Norway Triassic peneplains may have been buried in sediments to be re-exposed as coastal plains called strandflats. Dating of illite clay from a strandflat of Bømlo, southern Norway, have shown that landscape there became weathered in Late Triassic times with the landscape also being shaped during that time. At Paleorrota geopark, located in Rio Grande do Sul, the Santa Maria Formation and Caturrita Formations are exposed.
In these formations, one of the earliest dinosaurs, Staurikosaurus, as well as the mammal ancestors Brasilitherium and Brasilodon have been discovered. The Triassic continental interior climate was hot and dry, so that typical deposits are red bed sandstones and evaporites. There is no evidence of glaciation near either pole. Pangaea's large size limited the moderating effect of the global ocean; the strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons. The Triassic may have been a dry period, but evidence exists that it was punctuated by several episodes of increased rainfall in tropical and subtropical latitudes of the Tethys Sea and its surrounding land. Sediments and fossils suggestive of a more humid climate are known from the Anisian to Ladinian of the Tethysian domain, from the Carnian and Rhaetian of a larger area that includes the Boreal domain, the North
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene extinction event known as the Cretaceous–Tertiary extinction, was a sudden mass extinction of some three-quarters of the plant and animal species on Earth 66 million years ago. With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms survived, it marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks; the boundary clay shows high levels of the metal iridium, rare in the Earth's crust, but abundant in asteroids. As proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter Alvarez, it is now thought that the K–Pg extinction was caused by the impact of a massive comet or asteroid 10 to 15 km wide, 66 million years ago, which devastated the global environment through a lingering impact winter which halted photosynthesis in plants and plankton.
The impact hypothesis known as the Alvarez hypothesis, was bolstered by the discovery of the 180-kilometer-wide Chicxulub crater in the Gulf of Mexico's Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred provides strong evidence that they were caused by the asteroid. A 2016 drilling project into the Chicxulub peak ring, confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain. Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions, climate change, sea level change. A wide range of species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs.
It destroyed a plethora of other terrestrial organisms, including certain mammals, birds, lizards and plants. In the oceans, the K–Pg extinction killed off plesiosaurs and the giant marine lizards and devastated fish, sharks and many species of plankton, it is estimated. Yet the extinction provided evolutionary opportunities: in its wake, many groups underwent remarkable adaptive radiation—sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the Paleogene, evolving new forms such as horses, whales and primates. Birds and lizards radiated; the K–Pg boundary represents one of the most dramatic turnovers in the fossil record for various calcareous nanoplankton that formed the calcium deposits for which the Cretaceous is named. The turnover in this group is marked at the species level. Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a sharp increase in extinctions than by a decrease in speciation.
The K–Pg boundary record of dinoflagellates is not so well understood because only microbial cysts provide a fossil record, not all dinoflagellate species have cyst-forming stages, which causes diversity to be underestimated. Recent studies indicate that there were no major shifts in dinoflagellates through the boundary layer; the K–Pg extinction event was severe, global and selective, eliminating a vast number of species. Based on marine fossils, it is estimated; the event appears to have affected all continents at the same time. Non-avian dinosaurs, for example, are known from the Maastrichtian of North America, Asia, South America, Antarctica, but are unknown from the Cenozoic anywhere in the world. Fossil pollen shows devastation of the plant communities in areas as far apart as New Mexico, Alaska and New Zealand. Despite the event's severity, there was significant variability in the rate of extinction between and within different clades. Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked sunlight and reduced the solar energy reaching the ground.
This plant extinction caused a major reshuffling of the dominant plant groups. Omnivores and carrion-eaters survived the extinction event because of the increased availability of their food sources. No purely herbivorous or carnivorous mammals seem to have survived. Rather, the surviving mammals and birds fed on insects and snails, which in turn fed on detritus. In stream communities, few animal groups became extinct because such communities rely less directly on food from living plants and more on detritus washed in from the land, protecting them from extinction. Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the water column than among animals living on or in the sea floor. Animals in the water column are entirely dependent on primary production from living phytoplankton, while animals on the ocean floor always or sometimes feed on detritus. Coccolithophorids and mollusks, those organisms whose food chain included these shell builders, became extinct or suffered heavy losses.
For example, it is thought that
North America is a continent within the Northern Hemisphere and all within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16.5% of the earth's land area and about 4.8% of its total surface. North America is the third largest continent by area, following Asia and Africa, the fourth by population after Asia and Europe. In 2013, its population was estimated at nearly 579 million people in 23 independent states, or about 7.5% of the world's population, if nearby islands are included. North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge 40,000 to 17,000 years ago; the so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago. The Classic stage spans the 6th to 13th centuries.
The Pre-Columbian era ended in 1492, the transatlantic migrations—the arrival of European settlers during the Age of Discovery and the Early Modern period. Present-day cultural and ethnic patterns reflect interactions between European colonists, indigenous peoples, African slaves and their descendants. Owing to the European colonization of the Americas, most North Americans speak English, Spanish or French, their culture reflects Western traditions; the Americas are accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass unknown by Europeans. In 1507, Waldseemüller produced a world map, in which he placed the word "America" on the continent of South America, in the middle of what is today Brazil, he explained the rationale for the name in the accompanying book Cosmographiae Introductio:... ab Americo inventore... quasi Americi terram sive Americam.
For Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespucci's name, but in its feminine form "America", following the examples of "Europa", "Asia" and "Africa". Other mapmakers extended the name America to the northern continent, In 1538, Gerard Mercator used America on his map of the world for all the Western Hemisphere; some argue that because the convention is to use the surname for naming discoveries, the derivation from "Amerigo Vespucci" could be put in question. In 1874, Thomas Belt proposed a derivation from the Amerrique mountains of Central America. Marcou corresponded with Augustus Le Plongeon, who wrote: "The name AMERICA or AMERRIQUE in the Mayan language means, a country of perpetually strong wind, or the Land of the Wind, and... the can mean... a spirit that breathes, life itself." The United Nations formally recognizes "North America" as comprising three areas: Northern America, Central America, The Caribbean.
This has been formally defined by the UN Statistics Division. The term North America maintains various definitions in accordance with context. In Canadian English, North America refers to the land mass as a whole consisting of Mexico, the United States, Canada, although it is ambiguous which other countries are included, is defined by context. In the United States of America, usage of the term may refer only to Canada and the US, sometimes includes Greenland and Mexico, as well as offshore islands. In France, Portugal, Romania and the countries of Latin America, the cognates of North America designate a subcontinent of the Americas comprising Canada, the United States, Mexico, Greenland, Saint Pierre et Miquelon, Bermuda. North America has been referred to by other names. Spanish North America was referred to as Northern America, this was the first official name given to Mexico. Geographically the North American continent has many subregions; these include cultural and geographic regions. Economic regions included those formed by trade blocs, such as the North American Trade Agreement bloc and Central American Trade Agreement.
Linguistically and culturally, the continent could be divided into Latin America. Anglo-America includes most of Northern America and Caribbean islands with English-speaking populations; the southern North American continent is composed of two regions. These are the Caribbean; the north of the continent maintains recognized regions as well. In contrast to the common definition of "North America", which encompasses the whole continent, the term "North America" is sometimes used to refer only to Mexico, the United States, Greenland; the term Northern America refers to the northern-most countries and territories of North America: the United States, Bermuda, St. Pierre and Miquelon and Greenland. Although the term does not refer to a unifie
Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features. This includes aspects of the outward appearance, i.e. external morphology, as well as the form and structure of the internal parts like bones and organs, i.e. internal morphology. This is in contrast to physiology, which deals with function. Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts; the word "morphology" is from the Ancient Greek μορφή, morphé, meaning "form", λόγος, lógos, meaning "word, research". While the concept of form in biology, opposed to function, dates back to Aristotle, the field of morphology was developed by Johann Wolfgang von Goethe and independently by the German anatomist and physiologist Karl Friedrich Burdach. Among other important theorists of morphology are Lorenz Oken, Georges Cuvier, Étienne Geoffroy Saint-Hilaire, Richard Owen, Karl Gegenbaur and Ernst Haeckel.
In 1830, Cuvier and E. G. Saint-Hilaire engaged in a famous debate, said to exemplify the two major deviations in biological thinking at the time – whether animal structure was due to function or evolution. Comparative morphology is analysis of the patterns of the locus of structures within the body plan of an organism, forms the basis of taxonomical categorization. Functional morphology is the study of the relationship between the structure and function of morphological features. Experimental morphology is the study of the effects of external factors upon the morphology of organisms under experimental conditions, such as the effect of genetic mutation. "Anatomy" is a "branch of morphology that deals with the structure of organisms". Molecular Morphology is a term used in English-speaking countries for describing the structure of compound molecules, such as polymers and ribonucleic acid. Gross Morphology refers to the collective structures of an organism as a whole as a general description of the form and structure of an organism, taking into account all of its structures without specifying an individual structure.
Most taxa differ morphologically from other taxa. Related taxa differ much less than more distantly related ones, but there are exceptions to this. Cryptic species are species which look similar, or even outwardly identical, but are reproductively isolated. Conversely, sometimes unrelated taxa acquire a similar appearance as a result of convergent evolution or mimicry. In addition, there can be morphological differences within a species, such as in Apoica flavissima where queens are smaller than workers. A further problem with relying on morphological data is that what may appear, morphologically speaking, to be two distinct species, may in fact be shown by DNA analysis to be a single species; the significance of these differences can be examined through the use of allometric engineering in which one or both species are manipulated to phenocopy the other species. A step relevant to the evaluation of morphology between traits/features within species, includes an assessment of the terms: homology and homoplasy.
Homology between features indicate. Alternatively, homoplasy between features describes those that can resemble each other, but derive independently via parallel or convergent evolution. Invention and development of microscopy enable the observation of 3-D cell morphology with both high spatial and temporal resolution; the dynamic processes of these cell morphology which are controlled by a complex system play an important role in varied important biological process, such as immune and invasive responses. Comparative anatomy Insect morphology Morphometrics Neuromorphology Phenetics Phenotype Phenotypic plasticity Plant morphology Media related to Morphology at Wikimedia Commons