Lebanon known as the Lebanese Republic, is a country in Western Asia. It is bordered by Syria to the north and east and Israel to the south, while Cyprus is west across the Mediterranean Sea. Lebanon's location at the crossroads of the Mediterranean Basin and the Arabian hinterland facilitated its rich history and shaped a cultural identity of religious and ethnic diversity. At just 10,452 km2, it is the smallest recognized sovereign state on the mainland Asian continent; the earliest evidence of civilization in Lebanon dates back more than seven thousand years, predating recorded history. Lebanon was the home of the Canaanites/Phoenicians and their kingdoms, a maritime culture that flourished for over a thousand years. In 64 BC, the region came under the rule of the Roman Empire, became one of the Empire's leading centers of Christianity. In the Mount Lebanon range a monastic tradition known as the Maronite Church was established; as the Arab Muslims conquered the region, the Maronites held onto their identity.
However, a new religious group, the Druze, established themselves in Mount Lebanon as well, generating a religious divide that has lasted for centuries. During the Crusades, the Maronites re-established contact with the Roman Catholic Church and asserted their communion with Rome; the ties they established with the Latins have influenced the region into the modern era. The region was ruled by the Ottoman Empire from 1516 to 1918. Following the collapse of the empire after World War I, the five provinces that constitute modern Lebanon came under the French Mandate of Lebanon; the French expanded the borders of the Mount Lebanon Governorate, populated by Maronites and Druze, to include more Muslims. Lebanon gained independence in 1943, establishing confessionalism, a unique, Consociationalism-type of political system with a power-sharing mechanism based on religious communities. Bechara El Khoury, President of Lebanon during the independence, Riad El-Solh, first Lebanese prime minister and Emir Majid Arslan II, first Lebanese minister of defence, are considered the founders of the modern Republic of Lebanon and are national heroes for having led the country's independence.
Foreign troops withdrew from Lebanon on 31 December 1946, although the country was subjected to military occupations by Syria that lasted nearly thirty years before being withdrawn in April 2005 as well as the Israeli military in Southern Lebanon for fifteen years. Despite its small size, the country has developed a well-known culture and has been influential in the Arab world, powered by its large diaspora. Before the Lebanese Civil War, the country experienced a period of relative calm and renowned prosperity, driven by tourism, agriculture and banking; because of its financial power and diversity in its heyday, Lebanon was referred to as the "Switzerland of the East" during the 1960s, its capital, attracted so many tourists that it was known as "the Paris of the Middle East". At the end of the war, there were extensive efforts to revive the economy and rebuild national infrastructure. In spite of these troubles, Lebanon has the 7th highest Human Development Index and GDP per capita in the Arab world after the oil-rich economies of the Persian Gulf.
Lebanon has been a member of the United Nations since its founding in 1945 as well as of the Arab League, the Non-Aligned Movement, Organisation of the Islamic Cooperation and the Organisation internationale de la francophonie. The name of Mount Lebanon originates from the Phoenician root lbn meaning "white" from its snow-capped peaks. Occurrences of the name have been found in different Middle Bronze Age texts from the library of Ebla, three of the twelve tablets of the Epic of Gilgamesh; the name is recorded in Ancient Egyptian as Rmnn, where R stood for Canaanite L. The name occurs nearly 70 times in the Hebrew Bible, as לְבָנוֹן. Lebanon as the name of an administrative unit was introduced with the Ottoman reforms of 1861, as the Mount Lebanon Mutasarrifate, continued in the name of the State of Greater Lebanon in 1920, in the name of the sovereign Republic of Lebanon upon its independence in 1943; the borders of contemporary Lebanon are a product of the Treaty of Sèvres of 1920. Its territory was the core of the Bronze Age Phoenician city-states.
As part of the Levant, it was part of numerous succeeding empires throughout ancient history, including the Egyptian, Babylonian, Achaemenid Persian, Hellenistic and Sasanid Persian empires. After the 7th-century Muslim conquest of the Levant, it was part of the Rashidun, Abbasid Seljuk and Fatimid empires; the crusader state of the County of Tripoli, founded by Raymond IV of Toulouse in 1102, encompassed most of present-day Lebanon, falling to the Mamluk Sultanate in 1289 and to the Ottoman Empire in 1517. With the dissolution of the Ottoman Empire, Greater Lebanon fell under French mandate in 1920, gained independence under president Bechara El Khoury in 1943. Lebanon's history since independence has been marked by alternating periods of political stability and prosperity based on Beirut's position as a regional center for finance and trade, interspersed with political turmoil and
The subfamily Caprinae is part of the ruminant family Bovidae, consists of medium-sized bovids. A member of this subfamily is called a caprine. A member is sometimes referred to as a goat-antelope, this term "goat-antelope" does not mean that these animals are true antelopes: a true antelope is a bovid with a cervid-like or antilocaprid-like morphology. Within this subfamily Caprinae, a prominent tribe, includes sheep and goats; some earlier taxonomies considered Caprinae a separate family called Capridae, but now it is considered a subfamily within the family Bovidae, whence a caprine is a kind of bovid. Although most goat-antelopes are gregarious and have stocky builds, they diverge in many other ways – the muskox is adapted to the extreme cold of the tundra; the European mouflon is thought to be the ancestor of the modern domestic sheep. Many species have become extinct since the last ice age largely because of human interaction. Of the survivors: Five are classified as endangered, Eight as vulnerable, Seven as of concern and needing conservation measures, but at lower risk, Seven species are secure.
Members of the group vary in size, from just over 1 m long for a full-grown grey goral, to 2.5 m long for a musk ox, from under 30 kg to more than 350 kg. Musk oxen in captivity have reached over 650 kg; the lifestyles of caprids fall into two broad classes:'resource-defenders', which are territorial and defend a small, food-rich area against other members of the same species. The resource-defenders are the more primitive group: they tend to be smaller in size, dark in colour and females alike, have long, tassellated ears, long manes, dagger-shaped horns; the grazers evolved more recently. They tend to be larger social, rather than mark territory with scent glands, they have evolved dominance behaviours. No sharp line divides the groups, but a continuum varies from the serows at one end of the spectrum to sheep, true goats, musk oxen at the other; the goat-antelope, or caprid, group is known from as early as the Miocene, when members of the group resembled the modern serow in their general body form.
The group did not reach its greatest diversity until the recent ice ages, when many of its members became specialised for marginal extreme, environments: mountains and the subarctic region. The ancestors of the modern sheep and goats are thought to have moved into mountainous regions – sheep becoming specialised occupants of the foothills and nearby plains, relying on flight and flocking for defence against predators, goats adapting to steep terrain where predators are at a disadvantage. FAMILY BOVIDAE Subfamily Caprinae Tribe Ovibovini Genus Budorcas Takin, Budorcas taxicolor Genus Ovibos Muskox, Ovibos moschatus Tribe Caprini Genus Ammotragus Barbary sheep, Ammotragus lervia Genus Arabitragus Arabian tahr, Arabitragus jayakari Genus Capra West Caucasian tur, Capra caucasica East Caucasian tur, Capra caucasica cylindricornis Markhor, Capra falconeri Wild goat, Capra aegagrus Domestic goat, Capra aegagrus hircus Alpine ibex, Capra ibex Nubian ibex, Capra nubiana Spanish ibex, Capra pyrenaica Siberian ibex, Capra sibirica Walia ibex, Capra walie Genus Hemitragus Himalayan tahr, Hemitragus jemlahicus Genus Ovis Argali, Ovis ammon Domestic sheep, Ovis aries Bighorn sheep, Ovis canadensis Dall or thinhorn sheep, Ovis dalli European mouflon, Ovis musimon Marco Polo sheep, Ovis polii Snow sheep, Ovis nivicola Wild sheep, Ovis orientalis Mouflon, Ovis orientalis orientalis Urial, Ovis orientalis vignei Genus Nilgiritragus Nilgiri tahr, Nilgiritragus hylocrius Genus Pseudois Bharal, Pseudois nayaur Dwarf blue sheep, Pseudois schaeferi Tribe Naemorhedini Genus Capricornis Japanese serow, Capricornis crispus Sumatran serow, Capricornis sumatraensis Taiwan serow, Capricornis swinhoei Chinese serow, Capricornis milneedwardsii Red serow, Capricornis rubidus Himalayan serow Capricornis thar Genus Nemorhaedus Red goral, Nemorhaedus baileyi Chinese goral, Nemorhaedus griseus Grey goral, Nemorhaedus goral Long-tailed goral, Naemorhedus caudatus Genus Oreamnos Mountain goat, Oreamnos americanus Genus Rupicapra Pyrenean chamois, Rupicapra pyrenaica Alpine chamois, Rupicapra rupicapra The following extinct genera of Caprinae have been identified: Tribe Ovibovini Genus Bootherium † Bootherium bombifrons † Genus Euceratherium † Euceratherium collinum † Genus Makapania † Makapania broomi † Genus Soergelia † Soergelia mayfieldi † Genus Tsaidamotherium † Tsaidamotherium brevirostrum † Tsaidamotherium hedini † Tribe Caprini Genus Myotragus † Myotragus balearicus †Unsorted
Eritrea the State of Eritrea, is a country in the Horn of Africa, with its capital at Asmara. It is bordered by Sudan in the west, Ethiopia in the south, Djibouti in the southeast; the northeastern and eastern parts of Eritrea have an extensive coastline along the Red Sea. The nation has a total area of 117,600 km2, includes the Dahlak Archipelago and several of the Hanish Islands, its toponym Eritrea is based on the Greek name for the Red Sea, first adopted for Italian Eritrea in 1890. Eritrea is a multi-ethnic country, with nine recognized ethnic groups in its population of around 5 million. Most residents speak languages from the Afroasiatic family, either of the Ethiopian Semitic languages or Cushitic branches. Among these communities, the Tigrinyas make up about 55% of the population, with the Tigre people constituting around 30% of inhabitants. In addition, there are a number of Nilo-Saharan-speaking Nilotic ethnic minorities. Most people in the territory adhere to Islam; the Kingdom of Aksum, covering much of modern-day Eritrea and northern Ethiopia, was established during the first or second centuries AD.
It adopted Christianity around the middle of the fourth century. In medieval times much of Eritrea fell under the Medri Bahri kingdom, with a smaller region being part of Hamasien; the creation of modern-day Eritrea is a result of the incorporation of independent, distinct kingdoms and sultanates resulting in the formation of Italian Eritrea. After the defeat of the Italian colonial army in 1942, Eritrea was administered by the British Military Administration until 1952. Following the UN General Assembly decision, in 1952, Eritrea would govern itself with a local Eritrean parliament but for foreign affairs and defense it would enter into a federal status with Ethiopia for a period of 10 years. However, in 1962 the government of Ethiopia annulled the Eritrean parliament and formally annexed Eritrea, but the Eritreans that argued for complete Eritrean independence since the ouster of the Italians in 1941, anticipated what was coming and in 1960 organized the Eritrean Liberation Front in opposition.
In 1991, after 30 years of continuous armed struggle for independence, the Eritrean liberation fighters entered the capital city, Asmara, in victory. Eritrea is a one-party state in which national legislative elections have never been held since independence. According to Human Rights Watch, the Eritrean government's human rights record is among the worst in the world; the Eritrean government has dismissed these allegations as politically motivated. The compulsory military service requires long, indefinite conscription periods, which some Eritreans leave the country to avoid; because all local media is state-owned, Eritrea was ranked as having the second-least press freedom in the global Press Freedom Index, behind only North Korea. The sovereign state of Eritrea is a member of the African Union, the United Nations, the Intergovernmental Authority on Development, is an observer in the Arab League alongside Brazil, Venezuela and Turkey; the name Eritrea is derived from the ancient Greek name for the Red Sea.
It was first formally adopted with the formation of Italian Eritrea. The name persisted over the course of subsequent British and Ethiopian occupation, was reaffirmed by the 1993 independence referendum and 1997 constitution. At Buya in Eritrea, one of the oldest hominids representing a possible link between Homo erectus and an archaic Homo sapiens was found by Italian scientists. Dated to over 1 million years old, it is the oldest skeletal find of its kind and provides a link between hominids and the earliest anatomically modern humans, it is believed that the section of the Danakil Depression in Eritrea was a major player in terms of human evolution, may contain other traces of evolution from Homo erectus hominids to anatomically modern humans. During the last interglacial period, the Red Sea coast of Eritrea was occupied by early anatomically modern humans, it is believed that the area was on the route out of Africa that some scholars suggest was used by early humans to colonize the rest of the Old World.
In 1999, the Eritrean Research Project Team composed of Eritrean, American and French scientists discovered a Paleolithic site with stone and obsidian tools dated to over 125,000 years old near the Bay of Zula south of Massawa, along the Red Sea littoral. The tools are believed to have been used by early humans to harvest marine resources such as clams and oysters. According to linguists, the first Afroasiatic-speaking populations arrived in the region during the ensuing Neolithic era from the family's proposed urheimat in the Nile Valley. Other scholars propose that the Afroasiatic family developed in situ in the Horn, with its speakers subsequently dispersing from there. Together with Djibouti, northern Somalia, the Red Sea coast of Sudan, Eritrea is considered the most location of the land which the ancient Egyptians called Punt, first mentioned in the 25th century BC; the ancient Puntites had close relations with Ancient Egypt during the rule of Pharaoh Sahure and Queen Hatshepsut. This is confirmed by genetic studies of mummified baboons.
In 2010, a study was conducted on baboon mummies that were brought from Punt to Egypt as gifts by the ancient Egyptians. The scientists from the Egyptian Museum and the University of California used oxygen isotope analysis to examine hairs from two baboon mummies, preserved in the British Museum. One of the baboons had distorted isotopic data, so t
Habitat destruction is the process by which natural habitat becomes incapable of supporting its native species. In this process, the organisms that used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity is for the purpose of harvesting natural resources for industrial production and urbanization. Clearing habitats for agriculture is the principal cause of habitat destruction. Other important causes of habitat destruction include mining, logging and urban sprawl. Habitat destruction is ranked as the primary cause of species extinction worldwide, it is a process of natural environmental change that may be caused by habitat fragmentation, geological processes, climate change or by human activities such as the introduction of invasive species, ecosystem nutrient depletion, other human activities. The terms habitat loss and habitat reduction are used in a wider sense, including loss of habitat from other factors, such as water and noise pollution. In the simplest term, when a habitat is destroyed, the plants and other organisms that occupied the habitat have a reduced carrying capacity so that populations decline and extinction becomes more likely.
The greatest threat to organisms and biodiversity is the process of habitat loss. Temple found that 82% of endangered bird species were threatened by habitat loss. Most amphibian species are threatened by habitat loss, some species are now only breeding in modified habitat. Endemic organisms with limited ranges are most affected by habitat destruction because these organisms are not found anywhere else within the world, thus have less chance of recovering. Many endemic organisms have specific requirements for their survival that can only be found within a certain ecosystem, resulting in their extinction. Extinction may take place long after the destruction of habitat, a phenomenon known as extinction debt. Habitat destruction can decrease the range of certain organism populations; this can result in the reduction of genetic diversity and the production of infertile youths, as these organisms would have a higher possibility of mating with related organisms within their population, or different species.
One of the most famous examples is the impact upon China's giant panda, once found across the nation. Now it is only found in fragmented and isolated regions in the southwest of the country, as a result of widespread deforestation in the 20th century. Biodiversity hotspots are chiefly tropical regions that feature high concentrations of endemic species and, when all hotspots are combined, may contain over half of the world’s terrestrial species; these hotspots are suffering from habitat destruction. Most of the natural habitat on islands and in areas of high human population density has been destroyed. Islands suffering extreme habitat destruction include New Zealand, the Philippines, Japan. South and East Asia — China, Malaysia and Japan — and many areas in West Africa have dense human populations that allow little room for natural habitat. Marine areas close to populated coastal cities face degradation of their coral reefs or other marine habitat; these areas include the eastern coasts of Asia and Africa, northern coasts of South America, the Caribbean Sea and its associated islands.
Regions of unsustainable agriculture or unstable governments, which may go hand-in-hand experience high rates of habitat destruction. Central America, Sub-Saharan Africa, the Amazonian tropical rainforest areas of South America are the main regions with unsustainable agricultural practices and/or government mismanagement. Areas of high agricultural output tend to have the highest extent of habitat destruction. In the U. S. less than 25 % of native vegetation remains in many parts of the Midwest. Only 15% of land area remains unmodified by human activities in all of Europe. Tropical rainforests have received most of the attention concerning the destruction of habitat. From the 16 million square kilometers of tropical rainforest habitat that existed worldwide, less than 9 million square kilometers remain today; the current rate of deforestation is 160,000 square kilometers per year, which equates to a loss of 1% of original forest habitat each year. Other forest ecosystems have suffered as more destruction as tropical rainforests.
Farming and logging have disturbed at least 94% of temperate broadleaf forests. Tropical deciduous dry forests are easier to clear and burn and are more suitable for agriculture and cattle ranching than tropical rainforests. Plains and desert areas have been degraded to a lesser extent. Only 10-20% of the world's drylands, which include temperate grasslands and shrublands, deciduous forests, have been somewhat degraded, but included in that 10-20% of land is the 9 million square kilometers of seasonally dry-lands that humans have converted to deserts through the process of desertification. The tallgrass prairies of North America, on the other hand, have less than 3% of natural habitat remaining that has not been converted to farmland. Wetlands and marine areas have endured high levels of habitat destruction. More than 50% of wetlands in the U. S. have been destroyed in just the last 200 years. Between 60% and 70% of European wetlands have been destroyed. In the United Kingdom, there has been an i
Planet Earth (2006 TV series)
Planet Earth is a 2006 British television series produced by the BBC Natural History Unit. Five years in the making, it was the most expensive nature documentary series commissioned by the BBC and the first to be filmed in high definition; the series received multiple awards, including four Emmy Awards, a Peabody Award, an award from the Royal Television Society. Planet Earth premiered on 5 March 2006 in the United Kingdom on BBC One, by June 2007 had been shown in 130 countries; the original version was narrated by David Attenborough, whilst some international versions used alternative narrators. The series has eleven episodes, each of which features a global overview of a different biome or habitat on Earth. At the end of each fifty-minute episode, a ten-minute featurette takes a behind-the-scenes look at the challenges of filming the series. Ten years the BBC announced a six-part sequel had been commissioned, titled Planet Earth II, the first television series produced by the BBC in Ultra-high-definition.
David Attenborough returned as presenter. A second sequel, Planet Earth III is announced and planned to air in 2022. In 2001 the BBC broadcast a series on the natural history of the world's oceans, it received critical acclaim, high viewing figures, audience appreciation ratings, many awards. It became a hugely profitable global brand being sold to 150 countries worldwide. Feedback showed that audiences liked the epic scale, the scenes of new and unusual species and the cinematic quality of the series. Programme commissioners were keen for a follow-up, so Alastair Fothergill decided that the Natural History Unit should repeat the formula with a series looking at the whole planet; the idea for Planet Earth was born, the series was commissioned by Lorraine Heggessey Controller of BBC One, in January 2002. A feature film version of Planet Earth was commissioned alongside the television series, repeating the successful model established with The Blue Planet and its companion film, Deep Blue. Earth was released around the world from 2007 to 2009.
There was another accompanying television series, Planet Earth: The Future, which looked at the environmental problems facing some of the species and habitats featured in the main series in more detail. Planet Earth premiered on BBC One on 5 March 2006 in the United Kingdom. On the same day or in the subsequent weeks or months, the series began airing in several other countries. International broadcasters carrying Planet Earth include Australia on ABC and GEM, Canada on CBC and CTV, New Zealand on Prime, the Philippines on GMA Network and GMA News TV, the U. S. on Discovery Channel and Velocity and Science and Animal Planet and Destination America and BBC America. The episodes are each an hour in length, comprising the main programme and a 10-minute featurette called Planet Earth Diaries, which details the filming of a particular event. In the UK, Planet Earth was split into two parts, broadcast in spring and autumn 2006; the first five episodes premiered on BBC One at 9:00 pm on Sundays, beginning on 5 March 2006.
The programmes were repeated the following Saturday in an early evening slot on BBC Two. Along with its 2005 dramatisation of Bleak House, the BBC selected Planet Earth for its trial of high-definition broadcasts; the opening episode was its first-ever scheduled programme in the format, shown 27 May 2006 on the BBC HD channel. The first episode in the autumn series, Great Plains, received its first public showing at the Edinburgh International Television Festival on 26 August 2006, it was shown on a giant screen in Conference Square. The remaining episodes were broadcast from 5 November 2006 in the same primetime BBC One slot, following a further repeat run of the spring programmes on BBC Four; the autumn episodes were broadcast on BBC HD and were repeated on BBC Four the following week. Besides being BBC One's featured One to Watch programme of the day, Planet Earth was trailed on the BBC's television and radio channels both before and during its run; the music, featured in the BBC trailers for the series is the track "Hoppípolla" from the album Takk... by Icelandic post-rock band Sigur Rós.
Following the advertisements, interest was so widespread. In the United States, the series was promoted using "The Time Has Come" from trailer music company Epic Score, composed by Gabriel Shadid and Tobias Marberger; the Australian trailers used Jupiter: The Bringer of Jollity from Gustav Holst's orchestral suite The Planets, but reverted to "Hoppípolla". The BBC pre-sold the series to several overseas broadcasters, including the Discovery Channel for the United States, the Australian Broadcasting Corporation, the Canadian Broadcasting Corporation, China Central Television, WDR for Germany, Discovery Channel for India, Prime Television for New Zealand, C1R for Russian broadcasts; the series was sold to 130 countries. On 25 March 2007, the series began its run on American television on the Discovery network, premiering on the Discovery Channel and Discovery HD Theater. There were a number of revisions to the original British programme. Actress and conservationist Sigourney Weaver was brought in to replace David Attenborough as narrator, as it was thought her familiarity to American audiences would attract more viewers.
The Discovery programmes used a different script to the British original. The series was broadcast on Sundays in one 3-hour block followed by four 2-hour blocks; the Planet Earth Diaries segments were not shown after each episode, but collectively in Planet Earth: The Filmmakers' Story, a two-hour special, broadcast after the series had finished its initial network run. Edited versions w
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
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