The Caribbean is a region of The Americas that consists of the Caribbean Sea, its islands and the surrounding coasts. The region is southeast of the Gulf of Mexico and the North American mainland, east of Central America, north of South America. Situated on the Caribbean Plate, the region comprises more than 700 islands, islets and cays; these islands form island arcs that delineate the eastern and northern edges of the Caribbean Sea. The Caribbean islands, consisting of the Greater Antilles on the north and the Lesser Antilles on the south and east, are part of the somewhat larger West Indies grouping, which includes the Lucayan Archipelago; the Lucayans and, less Bermuda, are sometimes considered Caribbean despite the fact that none of these islands border the Caribbean Sea. In a wider sense, the mainland countries and territories of Belize, the Caribbean region of Colombia, the Yucatán Peninsula, Margarita Island, the Guyanas, are included due to their political and cultural ties with the region.
Geopolitically, the Caribbean islands are regarded as a subregion of North America and are organized into 30 territories including sovereign states, overseas departments, dependencies. From December 15, 1954, to October 10, 2010, there was a country known as the Netherlands Antilles composed of five states, all of which were Dutch dependencies. From January 3, 1958, to May 31, 1962, there was a short-lived political union called the West Indies Federation composed of ten English-speaking Caribbean territories, all of which were British dependencies; the West Indies cricket team continues to represent many of those nations. The region takes its name from that of the Caribs, an ethnic group present in the Lesser Antilles and parts of adjacent South America at the time of the Spanish conquest of the Americas; the two most prevalent pronunciations of "Caribbean" outside the Caribbean are, with the primary stress on the third syllable, with the stress on the second. Most authorities of the last century preferred the stress on the third syllable.
This is the older of the two pronunciations, but the stressed-second-syllable variant has been established for over 75 years. It has been suggested that speakers of British English prefer while North American speakers more use, but major American dictionaries and other sources list the stress on the third syllable as more common in American English too. According to the American version of Oxford Online Dictionaries, the stress on the second syllable is becoming more common in UK English and is considered "by some" to be more up to date and more "correct"; the Oxford Online Dictionaries claim that the stress on the second syllable is the most common pronunciation in the Caribbean itself, but according to the Dictionary of Caribbean English Usage, the most common pronunciation in Caribbean English stresses the first syllable instead. The word "Caribbean" has multiple uses, its principal ones are political. The Caribbean can be expanded to include territories with strong cultural and historical connections to slavery, European colonisation and the plantation system.
The United Nations geoscheme for the Americas presents the Caribbean as a distinct region within the Americas. Physiographically, the Caribbean region is a chain of islands surrounding the Caribbean Sea. To the north, the region is bordered by the Gulf of Mexico, the Straits of Florida and the Northern Atlantic Ocean, which lies to the east and northeast. To the south lies the coastline of the continent of South America. Politically, the "Caribbean" may be centred on socio-economic groupings found in the region. For example, the bloc known as the Caribbean Community contains the Co-operative Republic of Guyana, the Republic of Suriname in South America and Belize in Central America as full members. Bermuda and the Turks and Caicos Islands, which are in the Atlantic Ocean, are associate members of the Caribbean Community; the Commonwealth of the Bahamas is in the Atlantic and is a full member of the Caribbean Community. Alternatively, the organisation called the Association of Caribbean States consists of every nation in the surrounding regions that lie on the Caribbean, plus El Salvador, which lies on the Pacific Ocean.
According to the ACS, the total population of its member states is 227 million people. The geography and climate in the Caribbean region varies: Some islands in the region have flat terrain of non-volcanic origin; these islands include Aruba, Curaçao, Bonaire, the Cayman Islands, Saint Croix, the Bahamas, Antigua. Others possess rugged towering mountain-ranges like the islands of Saint Martin, Hispaniola, Puerto Rico, Dominica, Saba, Sint Eustatius, Saint Kitts, Saint Lucia, Saint Thomas, Saint John, Grenada, Saint Vincent, Guadeloupe and Trinidad and Tobago. Definitions of the terms Greater Antilles and Lesser Antilles vary; the Virgin Islands as part of the Puerto Rican bank are sometimes included with the Greater Antilles. The term Lesser Antilles is used to define an island arc that includes Grenada but excludes Trinidad and Tobago and the Leeward Antilles; the waters of the Caribbean Sea host large, migratory schools of fish and coral reef
The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, named after Cambria, the Latinised name for Wales, where rocks from this age were first studied; the Precambrian accounts for 88% of the Earth's geologic time. The Precambrian is an informal unit of geologic time, subdivided into three eons of the geologic time scale, it spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, when hard-shelled creatures first appeared in abundance. Little is known about the Precambrian, despite it making up seven-eighths of the Earth's history, what is known has been discovered from the 1960s onwards; the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, fossils from the Precambrian are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain buried beneath Phanerozoic strata.
It is thought that the Earth coalesced from material in orbit around the Sun at 4,543 Ma, may have been struck by a large planetesimal shortly after it formed, splitting off material that formed the Moon. A stable crust was in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma; the term "Precambrian" is recognized by the International Commission on Stratigraphy as the only "supereon" in geologic time. "Precambrian" is still used by geologists and paleontologists for general discussions not requiring the more specific eon names. As of 2010, the United States Geological Survey considers the term informal, lacking a stratigraphic rank. A specific date for the origin of life has not been determined. Carbon found in 3.8 billion-year-old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have been found in Western Australia. Probable fossils 100 million years older have been found in the same area.
However, there is evidence. There is a solid record of bacterial life throughout the remainder of the Precambrian. Excluding a few contested reports of much older forms from North America and India, the first complex multicellular life forms seem to have appeared at 1500 Ma, in the Mesoproterozoic era of the Proterozoic eon. Fossil evidence from the Ediacaran period of such complex life comes from the Lantian formation, at least 580 million years ago. A diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma; these are referred to as Vendian biota. Hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic eon. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale, including some which may represent stem groups of modern taxa; the increase in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life. While land seems to have been devoid of plants and animals and other microbes formed prokaryotic mats that covered terrestrial areas.
Tracks from an animal with leg like appendages have been found in what was mud 551 million years ago. Evidence of the details of plate motions and other tectonic activity in the Precambrian has been poorly preserved, it is believed that small proto-continents existed prior to 4280 Ma, that most of the Earth's landmasses collected into a single supercontinent around 1130 Ma. The supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch 2400–2100 Ma. One of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a "Snowball Earth"; the atmosphere of the early Earth is not well understood. Most geologists believe it was composed of nitrogen, carbon dioxide, other inert gases, was lacking in free oxygen. There is, evidence that an oxygen-rich atmosphere existed since the early Archean. At present, it is still believed that molecular oxygen was not a significant fraction of Earth's atmosphere until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism.
This radical shift from a chemically inert to an oxidizing atmosphere caused an ecological crisis, sometimes called the oxygen catastrophe. At first, oxygen would have combined with other elements in Earth's crust iron, removing it from the atmosphere. After the supply of oxidizable surfaces ran out, oxygen would have begun to accumulate in the atmosphere, the modern high-oxygen atmosphere would have developed. Evidence for this lies in older rocks that contain massive banded iron formations that were laid down as iron oxides. A terminology has evolved covering the early years of the Earth's existence, as radiometric dating has allowed real dates to be assigned to specific formations and features; the Precambrian is divided into
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
A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
In anatomy, the term rostrum is used for a number of phylogenetically unrelated structures in different groups of animals. In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes, it is a rigid structure, but can be connected by a hinged joint, as seen in Leptostraca. Among insects, the rostrum is the name for the piercing mouthparts of the order Hemiptera; the long snout of weevils may be called a rostrum. Gastropod molluscs proboscis. Cephalopod molluscs have hard beak-like mouthparts referred to as the rostrum. Invertebrate rostrums In mammals, the rostrum is that part of the cranium located in front of the zygomatic arches, where it holds the teeth and nasal cavity; the beak or snout of a vertebrate may be referred to as the rostrum. Some cetaceans, including toothed whales such as dolphins and beaked whales, have rostrums which evolved from their jawbones; the narwhal possesses a large rostrum. Some fish have permanently protruding rostrums. Billfish use rostrums to stun prey.
Paddlefish, goblin sharks and hammerhead sharks have rostrums packed with electroreceptors which signal the presence of prey by detecting weak electrical fields. Sawsharks and the critically endangered sawfish have rostrums which are both electro-sensitive and used for slashing; the rostrums extend ventrally in front of the fish. In the case of hammerheads the rostrum extends both laterally; the upper jawbones of some fish have evolved into rostrums Beak Nostril Snout
Euselachii are an infraclass of a class of cartilaginous fish. This group includes rays. Of the 14 orders that compose Euselachii, 8 belong to the sharks, 6 to the rays, without an intermediate taxon separating sharks of rays. For this reason, some authors have separated Euselachii in two: super-order Selachimorpha corresponding to orders of sharks. For those who do not recognize these two super-orders, Euselachii therefore has for synonyms Pleurotremata and Rajomorphii. Both oviparity and viviparity are found in Euselachii. Around 70% of sharks are viviparous, including some members of Carcharhiniformes such as requiem sharks and hammerhead sharks, while the remaining 30% of sharks as well as all rays are either oviparous or ovoviviparous. Euselachii Superorder Selachimorpha: Carcharhiniformes - ground sharks Heterodontiformes - bullhead sharks Hexanchiformes - six- and sevengill sharks Lamniformes - mackerel sharks Orectolobiformes - carpet sharks Pristiophoriformes - saw sharks Squaliformes - dogfish Squatiniformes - angel sharks Superorder Rajomorphii or Batoidea: Myliobatiformes - stingrays Pristiformes - sawfish Rajiformes - skates, sometimes in addition to guitarfish and wedgefish Rhiniformes - wedgefish Rhinobatiformes - guitarfish Torpediniformes - electric rays Euselachii incertae sedis†Ctenacanthiformes Cappetta 1988
The smalltooth sawfish is a species of sawfish in the family Pristidae. It is found in shallow tropical and subtropical waters in coastal and estuarine parts of the Atlantic. Reports from elsewhere are now believed to be misidentifications of other species of sawfish, it is a critically endangered species. The smalltooth sawfish is found in tropical and subtropical parts of the Atlantic, including the Caribbean and Gulf of Mexico, its original range was the smallest of the sawfish species, covering about 2,100,000 km2. In the west it once ranged from the United States in the east from Senegal to Angola. Today it has disappeared from much of its historical range. There are old reports from the Mediterranean Sea, but this involved vagrants. Smalltooth sawfish are found in coastal marine and estuarine brackish waters, it prefers water less than 8 m deep, but adults are seen offshore at depths of up to 122 m. During periods with increased salinity, juveniles have been seen far up rivers; this species is found in places with soft bottoms such as mud or sand, but may occur over hard rocky bottoms or at coral reefs.
They are found in areas with mangrove or seagrass. The lower water temperature limit is 16–18 °C; the smalltooth sawfish reputedly reaches a total length of up to 7.6 m, but this is an exaggeration and the largest confirmed size is 5.54 m. It weighs up to 350 kg, its upperparts are brownish-gray, bluish-gray or blackish, the underparts are whitish. Unlike the largetooth sawfish, the only other sawfish in the Atlantic, the smalltooth sawfish has a leading edge of the dorsal fin, placed above the leading edge of the pelvic fins short pectoral fins and lack of a distinct lower lobe to the tail, it can be separated from the more similar dwarf sawfish and green sawfish by the distribution and the dorsal fin. The smalltooth sawfish has a narrow rostrum with 20–32 teeth on each side. For many years, rarity of seeing a sawfish in the wild prevented scientists from collecting conclusive evidence about the use of their distinctive rostrum; this led them to falsely assume that the sawfish, like many other marine vertebrates with a "beak," or an elongated rostrum, follow the rule that the appendage is used to either sense prey or capture prey, but never both.
There are no other studied marine animals with similar rostral characteristics that have shown that the rostrum is used for both of these feeding techniques. Recent studies have demonstrated, that the sawfish utilize their rostrum to both sense and manipulate prey. A sawfish's saw is made up of thousands of sensory organs that allow them to detect and monitor the movements of other organisms by measuring the electric fields they emit; the sensory organs called ampullary pores, are packed most densely on the dorsal side of its beak. This allows the fish to create an image of the three-dimensional area above it in waters of low-visibility; this provides support for the bottom-dwelling behavior of sawfish. Utilizing their saw as an extended sensing device, sawfish are able to "view" their entire surroundings by maintaining a position low to the sea floor. Sawfish uncover sand dwelling crustaceans and mollusks, two common prey types, by using their unique anatomical structure as a tool for digging and grubbing about in sand or mud.
The sawfish churn up the sea bottom with their exaggerated rostrum to uncover these hidden food sources. It is believed. Smalltooth sawfish have been observed to approach large shoals of fish while striking their saw from side to side. Due to the high density of small fish in a shoal, there is a high probability that the sawfish will hit, stun, or kill several prey during one shoal attack. Vertebrate biologist Barbara Wueringer, of the University of Queensland, demonstrated that sawfish use their extended rostrum to detect and manipulate prey, she observed the animals' reaction to food at the bottom of the tank, food falling from the water's surface, introduced electric dipoles. When the sawfish came across scraps of fish resting on the bottom of the tank, it used its rostrum to pin the "prey" down as it swam over and engulfed it; when food was identified as it fell through the water, the sawfish would approach its "prey" from the side and swiftly strike to impale the victim with the teeth of its saw.
Both of these cases support the respective digging and attacking behaviors expected from feeding sawfish in the wild. In order to show that sawfish use their beak to sense their surroundings, Wueringer placed electric dipoles throughout the tank to simulate the electrical signals that surround moving prey. Just as the sawfish displayed different aggressive behaviors towards the "prey," they responded differently based on the electrical signals they received by either avoiding or approaching the signal source. With this evidence, the sawfish is now regarded as the only jawed fish to use its rostrum for both prey detection and manipulation; the many teeth of a sawfish's saw are not teeth at all, but rather special types of scales known a dermal denticles. These protruding weapons, combined with the animal's ability to strike from side to side with great force, provide it with a powerful and efficient defense mechanism. Although