1.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
2.
Animal
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Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, arthropods, annelids, nematodes, flatworms, cnidarians, ctenophores, the study of animals is called zoology. The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms, Metazoa and Protozoa. The protozoa were later moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
3.
Chordate
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Chordates are deuterostomes, as during the embryo development stage the anus forms before the mouth. They are also bilaterally symmetric coelomates, in the case of vertebrate chordates, the notochord is usually replaced by a vertebral column during development, and they may have body plans organized via segmentation. There are also additional extinct taxa, the Vertebrata are sometimes considered as a subgroup of the clade Craniata, consisting of chordates with a skull, the Craniata and Tunicata compose the clade Olfactores. Of the more than 65,000 living species of chordates, the worlds largest and fastest animals, the blue whale and peregrine falcon respectively, are chordates, as are humans. Fossil chordates are known from at least as early as the Cambrian explosion, Hemichordata, which includes the acorn worms, has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum. The Hemichordata, along with the Echinodermata, form the Ambulacraria, the Chordata and Ambulacraria form the superphylum Deuterostomia, composed of the deuterostomes. Attempts to work out the relationships of the chordates have produced several hypotheses. All of the earliest chordate fossils have found in the Early Cambrian Chengjiang fauna. Because the fossil record of early chordates is poor, only molecular phylogenetics offers a prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial and it has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce family trees shows that many of the traditional classes are paraphyletic. While this has been known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in a state of flux. Although the name Chordata is attributed to William Bateson, it was already in prevalent use by 1880, ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization, among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail. In fish and other vertebrates, this develops into the spinal cord, the pharynx is the part of the throat immediately behind the mouth. In fish, the slits are modified to form gills, a muscular tail that extends backwards behind the anus. This is a groove in the wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus and it also stores iodine, and may be a precursor of the vertebrate thyroid gland
4.
Actinopterygii
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Actinopterygii /ˌæktᵻnˌɒptəˈrɪdʒi. aɪ/, or the ray-finned fishes, constitute a class or subclass of the bony fishes. These actinopterygian fin rays attach directly to the proximal or basal skeletal elements, the radials, numerically, actinopterygians are the dominant class of vertebrates, comprising nearly 99% of the over 30,000 species of fish. They are ubiquitous throughout freshwater and marine environments from the sea to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm, to the ocean sunfish, at 2,300 kg. Ray-finned fishes occur in variant forms. The main features of a typical ray-finned fish are shown in the diagram at the left. In nearly all ray-finned fish, the sexes are separate, development then proceeds with a free-swimming larval stage. However other patterns of ontogeny exist, with one of the commonest being sequential hermaphroditism, in most cases this involves protogyny, fish starting life as females and converting to males at some stage, triggered by some internal or external factor. This may be advantageous as females become less prolific as they age while male fecundity increases with age, protandry, where a fish converts from male to female, is much less common than protogyny. Most families use external rather than internal fertilization, of the oviparous teleosts, most do not provide parental care. Viviparity is relatively rare and is found in about 6% of teleost species, male territoriality preadapts a species for evolving male parental care. There are a few examples of fish that self-fertilise, the mangrove rivulus is an amphibious, simultaneous hermaphrodite, producing both eggs and spawn and having internal fertilisation. This mode of reproduction may be related to the habit of spending long periods out of water in the mangrove forests it inhabits. Males are occasionally produced at temperatures below 19 °C and can fertilise eggs that are spawned by the female. This maintains genetic variability in a species that is otherwise highly inbred, the earliest known fossil actinopterygiian is Andreolepis hedei, dating back 420 million years. Remains have been found in Russia, Sweden, and Estonia, actinopterygians are divided into the subclasses Chondrostei and Neopterygii. The Neopterygii, in turn, are divided into the infraclasses Holostei and Teleostei, during the Mesozoic and Cenozoic the teleosts in particular diversified widely, and as a result, 96% of all known fish species are teleosts. The cladogram shows the groups of actinopterygians and their relationship to the terrestrial vertebrates that evolved from a related group of fish
5.
Australia
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Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the worlds sixth-largest country by total area, the neighbouring countries are Papua New Guinea, Indonesia and East Timor to the north, the Solomon Islands and Vanuatu to the north-east, and New Zealand to the south-east. Australias capital is Canberra, and its largest urban area is Sydney, for about 50,000 years before the first British settlement in the late 18th century, Australia was inhabited by indigenous Australians, who spoke languages classifiable into roughly 250 groups. The population grew steadily in subsequent decades, and by the 1850s most of the continent had been explored, on 1 January 1901, the six colonies federated, forming the Commonwealth of Australia. Australia has since maintained a liberal democratic political system that functions as a federal parliamentary constitutional monarchy comprising six states. The population of 24 million is highly urbanised and heavily concentrated on the eastern seaboard, Australia has the worlds 13th-largest economy and ninth-highest per capita income. With the second-highest human development index globally, the country highly in quality of life, health, education, economic freedom. The name Australia is derived from the Latin Terra Australis a name used for putative lands in the southern hemisphere since ancient times, the Dutch adjectival form Australische was used in a Dutch book in Batavia in 1638, to refer to the newly discovered lands to the south. On 12 December 1817, Macquarie recommended to the Colonial Office that it be formally adopted, in 1824, the Admiralty agreed that the continent should be known officially as Australia. The first official published use of the term Australia came with the 1830 publication of The Australia Directory and these first inhabitants may have been ancestors of modern Indigenous Australians. The Torres Strait Islanders, ethnically Melanesian, were originally horticulturists, the northern coasts and waters of Australia were visited sporadically by fishermen from Maritime Southeast Asia. The first recorded European sighting of the Australian mainland, and the first recorded European landfall on the Australian continent, are attributed to the Dutch. The first ship and crew to chart the Australian coast and meet with Aboriginal people was the Duyfken captained by Dutch navigator, Willem Janszoon. He sighted the coast of Cape York Peninsula in early 1606, the Dutch charted the whole of the western and northern coastlines and named the island continent New Holland during the 17th century, but made no attempt at settlement. William Dampier, an English explorer and privateer, landed on the north-west coast of New Holland in 1688, in 1770, James Cook sailed along and mapped the east coast, which he named New South Wales and claimed for Great Britain. The first settlement led to the foundation of Sydney, and the exploration, a British settlement was established in Van Diemens Land, now known as Tasmania, in 1803, and it became a separate colony in 1825. The United Kingdom formally claimed the part of Western Australia in 1828. Separate colonies were carved from parts of New South Wales, South Australia in 1836, Victoria in 1851, the Northern Territory was founded in 1911 when it was excised from South Australia
6.
Coral reef
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Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups, the polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support, most reefs grow best in warm, shallow, clear, sunny and agitated waters. Often called rainforests of the sea, shallow coral reefs form some of the most diverse ecosystems on Earth, paradoxically, coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients. They are most commonly found at depths in tropical waters. Coral reefs deliver ecosystem services to tourism, fisheries and shoreline protection, the annual global economic value of coral reefs is estimated between US$29. 8-375 billion. However, coral reefs are fragile ecosystems, partly because they are sensitive to water temperature. Most of the coral reefs we can see today were formed after the last glacial period when melting ice caused the sea level to rise and this means that most modern coral reefs are less than 10,000 years old. As communities established themselves on the shelves, the reefs grew upwards, Reefs that rose too slowly could become drowned reefs. They are covered by so much water there was insufficient light. Coral reefs are found in the sea away from continental shelves, around oceanic islands. The vast majority of islands are volcanic in origin. The few exceptions have tectonic origins where plate movements have lifted the deep ocean floor on the surface. In 1842 in his first monograph, The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs and he theorized uplift and subsidence of the Earths crust under the oceans formed the atolls. Darwin’s theory sets out a sequence of three stages in atoll formation and it starts with a fringing reef forming around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the reef becomes a barrier reef. Darwin predicted that underneath each lagoon would be a bed rock base, where the level of the underlying earth allows, the corals grow around the coast to form what he called fringing reefs, and can eventually grow out from the shore to become a barrier reef
7.
Queensland
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Queensland is the second-largest and third-most-populous state in the Commonwealth of Australia. Situated in the north-east of the country, it is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west, to the east, Queensland is bordered by the Coral Sea and Pacific Ocean. Queensland has a population of 4,750,500, concentrated along the coast, the state is the worlds sixth largest sub-national entity, with an area of 1,852,642 km2. The capital and largest city in the state is Brisbane, Australias third largest city, often referred to as the Sunshine State, Queensland is home to 10 of Australias 30 largest cities and is the nations third largest economy. Tourism in the state, fuelled largely by its tropical climate, is a major industry. Queensland was first inhabited by Aboriginal Australians and Torres Strait Islanders, the first European to land in Queensland was Dutch navigator Willem Janszoon in 1606, who explored the west coast of the Cape York Peninsula near present-day Weipa. In 1770, Lieutenant James Cook claimed the east coast of Australia for the Kingdom of Great Britain. The colony of New South Wales was founded in 1788 by Governor Arthur Phillip at Sydney, New South Wales at that time included all of what is now Queensland, Queensland was explored in subsequent decades until the establishment of a penal colony at Brisbane in 1824 by John Oxley. Penal transportation ceased in 1839 and free settlement was allowed from 1842, the state was named in honour of Queen Victoria, who on 6 June 1859 signed Letters Patent separating the colony from New South Wales. The 6th of June is now celebrated statewide as Queensland Day. Queensland achieved statehood with the Federation of Australia on 1 January 1901, the history of Queensland spans thousands of years, encompassing both a lengthy indigenous presence, as well as the eventful times of post-European settlement. The north-eastern Australian region was explored by Dutch, Spanish and French navigators before being encountered by Lieutenant James Cook in 1770, the Australian Labor Party has its origin as a formal organisation in Queensland and the town of Barcaldine is the symbolic birthplace of the party. June 2009 marked the 150th anniversary of its creation as a colony from New South Wales. The Aboriginal occupation of Queensland is thought to predate 50,000 BC, likely via boat or land bridge across Torres Strait, during the last ice age Queenslands landscape became more arid and largely desolate, making food and other supplies scarce. This led to the worlds first seed-grinding technology, warming again made the land hospitable, which brought high rainfall along the eastern coast, stimulating the growth of the states tropical rainforests. In February 1606, Dutch navigator Willem Janszoon landed near the site of what is now Weipa and this was the first recorded landing of a European in Australia, and it also marked the first reported contact between European and Aboriginal Australian people. The region was explored by French and Spanish explorers prior to the arrival of Lieutenant James Cook in 1770. Cook claimed the east coast under instruction from King George III of the United Kingdom on 22 August 1770 at Possession Island, naming Eastern Australia, including Queensland, the Aboriginal population declined significantly after a smallpox epidemic during the late 18th century
8.
Persian Gulf
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The Persian Gulf is a mediterranean sea in Western Asia. The body of water is an extension of the Indian Ocean through the Strait of Hormuz, the Shatt al-Arab river delta forms the northwest shoreline. The Persian Gulf was a battlefield of the 1980–1988 Iran–Iraq War and it is the namesake of the 1991 Gulf War, the largely air- and land-based conflict that followed Iraqs invasion of Kuwait. The gulf has many fishing grounds, extensive coral reefs, and abundant pearl oysters, the body of water is historically and internationally known as the Persian Gulf. Some Arab governments refer to it as the Arabian Gulf or The Gulf, the name Gulf of Iran is used by the International Hydrographic Organization. The Persian Gulf is geologically young, having been formed around 15,000 years ago. Its length is 989 kilometres, with Iran covering most of the northern coast, the Persian Gulf is about 56 km wide at its narrowest, in the Strait of Hormuz. The waters are very shallow, with a maximum depth of 90 metres. Various small islands lie within the Persian Gulf, some of which are the subject of territorial disputes between the states of the region. The International Hydrographic Organization defines the Persian Gulfs southern limit as The Northwestern limit of Gulf of Oman and this limit is defined as A line joining Ràs Limah on the coast of Arabia and Ràs al Kuh on the coast of Iran. The Persian Gulf and its areas are the worlds largest single source of crude oil. Safaniya Oil Field, the worlds largest offshore oilfield, is located in the Persian Gulf, large gas finds have also been made, with Qatar and Iran sharing a giant field across the territorial median line. Using this gas, Qatar has built up a substantial liquefied natural gas, the oil-rich countries that have a coastline on the Persian Gulf are referred to as the Persian Gulf States. In 550 BC, the Achaemenid Empire established the first ancient empire in Persis, consequently, in the Greek sources, the body of water that bordered this province came to be known as the Persian Gulf. In the travel account of Pythagoras, several chapters are related to description of his travels accompanied by the Achaemenid king Darius the Great, to Susa and Persepolis, and the area is described. This water channel separates the Iran Plateau from the Arabia Plate, has enjoyed an Iranian Identity since at least 2200 years ago. Before being given its present name, the Persian Gulf was called many different names, the classical Greek writers, like Herodotus, called it the Red Sea. In Babylonian texts, it was known as the sea above Akkad, the name of the gulf, historically and internationally known as the Persian Gulf after the land of Persia, has been disputed by some Arab countries since the 1960s
9.
Estuary
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An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a zone between river environments and maritime environments. They are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The inflows of sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world. Most existing estuaries formed during the Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea began to rise about 10. Estuaries are typically classified according to their geomorphological features or to water-circulation patterns, the banks of many estuaries are amongst the most heavily populated areas of the world, with about 60% of the worlds population living along estuaries and the coast. The word estuary is derived from the Latin word aestuarium meaning tidal inlet of the sea, there have been many definitions proposed to describe an estuary. However, this definition excludes a number of water bodies such as coastal lagoons. This broad definition also includes fjords, lagoons, river mouths, an estuary is a dynamic ecosystem having a connection to the open sea through which the sea water enters with the rhythm of the tides. The sea water entering the estuary is diluted by the water flowing from rivers. The pattern of dilution varies between different estuaries and depends on the volume of water, the tidal range. Drowned river valleys are known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and this is the most common type of estuary in temperate climates. Well-studied estuaries include the Severn Estuary in the United Kingdom and the Ems Dollard along the Dutch-German border, the width-to-depth ratio of these estuaries is typically large, appearing wedge-shaped in the inner part and broadening and deepening seaward. Water depths rarely exceed 30 m, examples of this type of estuary in the U. S. are the Hudson River, Chesapeake Bay, and Delaware Bay along the Mid-Atlantic coast, and Galveston Bay and Tampa Bay along the Gulf Coast. They are relatively common in tropical and subtropical locations and these estuaries are semi-isolated from ocean waters by barrier beaches. Formation of barrier beaches partially encloses the estuary, with only narrow inlets allowing contact with the ocean waters, bar-built estuaries typically develop on gently sloping plains located along tectonically stable edges of continents and marginal sea coasts. They are extensive along the Atlantic and Gulf coasts of the U. S. in areas with active coastal deposition of sediments, barrier beaches form in shallow water and are generally parallel to the shoreline, resulting in long, narrow estuaries
10.
Brisbane River
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The Brisbane River is the longest river in South East Queensland, Australia, and flows through the city of Brisbane, before emptying into Moreton Bay. John Oxley, the first European to explore the river, named it after the Governor of New South Wales, the penal colony of Moreton Bay later adopted the same name, eventually becoming the present city of Brisbane. Early travellers along the waterway admired the beauty, abundant fish. From 1862 the Brisbane River has been dredged for navigation purposes, the river served as an important carriageway between Brisbane and Ipswich before a railway linking the towns was built in 1875. By the late 1920s, water quality in the river had significantly deteriorated, the river travels 344 km from Mount Stanley. The river is dammed by the Wivenhoe Dam, forming Lake Wivenhoe, the waterway is a habitat for the rare Queensland lungfish, Brisbane River cod and bull sharks. The largest ship built on the river was the Robert Miller, the 66,000 tonne vessel became un-moored in the 1974 Brisbane flood. While not the highest experienced along the river since European settlement, major floods also occurred in January 2011 and multiple times during 1893. Extensive port facilities have been constructed on the Fisherman Islands, now known as the Port of Brisbane, there are 16 major bridges that cross the river. The Clem Jones Tunnel, opened in 2010, is the rivers first underground crossing for road transport, the CityCat ferry service collects and delivers passengers along the inner-city reaches of the river. Brisbane Rivers source is located in the Great Dividing Range, east of Kingaroy and it then makes its way south, past Mount Stanley, and townships including Moore and Toogoolawah before being joined by the Stanley River, just south of Somerset Dam. The river runs from there into Lake Wivenhoe, created by the Wivenhoe Dam, beyond the dam, the river meanders eastward, meeting the Bremer River near Ipswich, then making its way through Brisbanes western suburbs, including Jindalee, Indooroopilly and Toowong. The river is traversed by CityCats and other ferries in Brisbane, Water from the highest point in the catchment has fallen from Mount Langley in the Conondale Range,868 m above sea level. On the southern side of the river, opposite Gardens Point, are the Kangaroo Point Cliffs and this was in the vicinity of Edward Street ferry terminal. The volcanic rock Ignimbrite which formed the cliffs was deposited in the Triassic period about 220 million years ago and they currently form the banks of the Brisbane River. On the southside Bulimba Creek, Norman Creek, Oxley Creek, the language group common to most of the area was the Yugarabul language group. Four European navigators, namely Captain Cook, Matthew Flinders, John Bingle and William Edwardson, all visited Moreton Bay, the exploration by Flinders took place during his expedition from Port Jackson north to Hervey Bay in 1799. He spent a total of 15 days in the area, touching down at Woody Point and several other spots and this is consistent with accounts of many other rivers along the east coast of Australia, which could not be found by seaward exploration but were discovered by inland travellers
11.
Shark
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Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha and are the group to the rays. Under this broader definition, the earliest known sharks date back to more than 420 million years ago, acanthodians are often referred to as spiny sharks, though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole. Since then, sharks have diversified into over 500 species, Sharks are found in all seas and are common to depths of 2,000 metres. They generally do not live in freshwater although there are a few exceptions, such as the bull shark and the river shark. Sharks have a covering of dermal denticles that protects their skin from damage and they have numerous sets of replaceable teeth. Well-known species such as the white shark, tiger shark, blue shark, mako shark. Many shark populations are threatened by human activities, until the 16th century, sharks were known to mariners as sea dogs. The etymology of the shark is uncertain. One theory is that it derives from the Yucatec Maya word xok, however, the Middle English Dictionary records an isolated occurrence of the word shark in a letter written by Thomas Beckington in 1442, which rules out a New World etymology. Evidence for the existence of sharks dates from the Ordovician period, 450–420 million years ago, before land vertebrates existed and before many plants had colonized the continents. Only scales have been recovered from the first sharks and not all agree that these are from true sharks. The oldest generally accepted shark scales are from about 420 million years ago, the first sharks looked very different from modern sharks. The majority of sharks can be traced back to around 100 million years ago. Most fossils are of teeth, often in large numbers, partial skeletons and even complete fossilized remains have been discovered. Estimates suggest that sharks grow tens of thousands of teeth over a lifetime, the teeth consist of easily fossilized calcium phosphate, an apatite. When a shark dies, the decomposing skeleton breaks up, scattering the apatite prisms, preservation requires rapid burial in bottom sediments. Among the most ancient and primitive sharks is Cladoselache, from about 370 million years ago, which has been found within Paleozoic strata in Ohio, Kentucky, and Tennessee
12.
Sea turtle
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Sea turtles, sometimes called marine turtles, are reptiles of the order Testudines. The seven extant species of sea turtles are, the green, loggerhead, Kemps ridley, olive ridley, hawksbill, flatback, the majority of a sea turtles body is protected by its shell. The turtles shell is divided two sections, carapace and plastron. The shell is made up of plates called scutes. The leatherback is the sea turtle that does not have a hard shell. Instead, it bears a mosaic of bony plates beneath its leathery skin, in general, sea turtles have a more fusiform body plan than their terrestrial or freshwater counterparts. The reduced volume of a body means sea turtles can not retract their head, legs. However this more stream-line body plan reduces drag in the water, the leatherback is the largest species of sea turtle. Measuring 2-3 meters in length, and 1-1.5 m in width, other species are smaller, being mostly 60-120 cm and proportionally narrower. Sea turtles, along with turtles and tortoises, are part of the order Testudines. All species except the leatherback are in the family Cheloniidae, the leatherback is the only extant member of the family Dermochelyidae. The origin of sea turtles back to the Late Jurassic with genera such as Plesiochelys. In Africa, the first marine turtle is Angolachelys, from the Turonian of Angola, however, neither of these are related to extant sea turtles, the oldest representative of the lineage leading to these was Desmatochelys padillai, from the Early Cretaceous. A lineage of unrelated marine testudines, the pleurodire bothremydids, also survived well into the Cenozoic, Sea turtles constitute a single radiation that became distinct from all other turtles at least 110 million years ago. The flatback sea turtle is found solely on the northern coast of Australia, the Kemps ridley sea turtle is found solely in the Gulf of Mexico and along the East Coast of the United States. Sea turtles are found in the waters over continental shelves. During the first three to five years of life, sea turtles spend most of their time in the pelagic zone floating in seaweed mats, Green sea turtles in particular are often found in Sargassum mats, in which they find shelter and food. Once the sea turtle has reached adulthood it moves closer to the shore, females will come ashore to lay their eggs on sandy beaches during the nesting season
