South Africa the Republic of South Africa, is the southernmost country in Africa. It is bounded to the south by 2,798 kilometres of coastline of Southern Africa stretching along the South Atlantic and Indian Oceans. South Africa is the largest country in Southern Africa and the 25th-largest country in the world by land area and, with over 57 million people, is the world's 24th-most populous nation, it is the southernmost country on the mainland of the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different African languages, nine of which have official status; the remaining population consists of Africa's largest communities of European and multiracial ancestry. South Africa is a multiethnic society encompassing a wide variety of cultures and religions, its pluralistic makeup is reflected in the constitution's recognition of 11 official languages, the fourth highest number in the world. Two of these languages are of European origin: Afrikaans developed from Dutch and serves as the first language of most coloured and white South Africans.
The country is one of the few in Africa never to have had a coup d'état, regular elections have been held for a century. However, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a large role in the country's recent history and politics; the National Party imposed apartheid in 1948. After a long and sometimes violent struggle by the African National Congress and other anti-apartheid activists both inside and outside the country, the repeal of discriminatory laws began in 1990. Since 1994, all ethnic and linguistic groups have held political representation in the country's liberal democracy, which comprises a parliamentary republic and nine provinces. South Africa is referred to as the "rainbow nation" to describe the country's multicultural diversity in the wake of apartheid; the World Bank classifies South Africa as an upper-middle-income economy, a newly industrialised country.
Its economy is the second-largest in Africa, the 34th-largest in the world. In terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa; however and inequality remain widespread, with about a quarter of the population unemployed and living on less than US$1.25 a day. South Africa has been identified as a middle power in international affairs, maintains significant regional influence; the name "South Africa" is derived from the country's geographic location at the southern tip of Africa. Upon formation, the country was named the Union of South Africa in English, reflecting its origin from the unification of four separate British colonies. Since 1961, the long form name in English has been the "Republic of South Africa". In Dutch, the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika. Since 1994, the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning "south", is a colloquial name for South Africa, while some Pan-Africanist political parties prefer the term "Azania".
South Africa contains human-fossil sites in the world. Archaeologists have recovered extensive fossil remains from a series of caves in Gauteng Province; the area, a UNESCO World Heritage site, has been branded "the Cradle of Humankind". The sites include one of the richest sites for hominin fossils in the world. Other sites include Gondolin Cave Kromdraai, Coopers Cave and Malapa. Raymond Dart identified the first hominin fossil discovered in Africa, the Taung Child in 1924. Further hominin remains have come from the sites of Makapansgat in Limpopo Province and Florisbad in the Free State Province, Border Cave in KwaZulu-Natal Province, Klasies River Mouth in Eastern Cape Province and Pinnacle Point and Die Kelders Cave in Western Cape Province; these finds suggest that various hominid species existed in South Africa from about three million years ago, starting with Australopithecus africanus. There followed species including Australopithecus sediba, Homo ergaster, Homo erectus, Homo rhodesiensis, Homo helmei, Homo naledi and modern humans.
Modern humans have inhabited Southern Africa for at least 170,000 years. Various researchers have located pebble tools within the Vaal River valley. Settlements of Bantu-speaking peoples, who were iron-using agriculturists and herdsmen, were present south of the Limpopo River by the 4th or 5th century CE, they displaced and absorbed the original Khoisan speakers, the Khoikhoi and San peoples. The Bantu moved south; the earliest ironworks in modern-day KwaZulu-Natal Province are believed to date from around 1050. The southernmost group was the Xhosa people, whose language incorporates certain linguistic traits from the earlier Khoisan people; the Xhosa reached the Great Fish River, in today's Eastern Cape Province. As they migrated, these larger Iron Age populations
Turtles are diapsids of the order Testudines characterized by a special bony or cartilaginous shell developed from their ribs and acting as a shield. "Turtle" may refer to fresh-water and sea-dwelling testudines. The order Testudines includes both extinct species; the earliest known members of this group date from 220 million years ago, making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians. Of the 356 known species alive today, some are endangered. Turtles are ectotherms—animals called cold-blooded—meaning that their internal temperature varies according to the ambient environment. However, because of their high metabolic rate, leatherback sea turtles have a body temperature, noticeably higher than that of the surrounding water. Turtles are classified as amniotes, along with other reptiles and mammals. Like other amniotes, turtles breathe air and do not lay eggs underwater, although many species live in or around water; the study of turtles is called cheloniology, after the Greek word for turtle.
It is sometimes called testudinology, after the Latin name for turtles. Differences exist in usage of the common terms turtle and terrapin, depending on the variety of English being used; these terms do not reflect precise biological or taxonomic distinctions. Turtle may either refer to the order as a whole, or to particular turtles that make up a form taxon, not monophyletic, or may be limited to only aquatic species. Tortoise refers to any land-dwelling, non-swimming chelonian. Terrapin is used to describe several species of small, hard-shell turtles those found in brackish waters. In North America, all chelonians are called turtles. Tortoise is used only in reference to terrestrial turtles or, more narrowly, only those members of Testudinidae, the family of modern land tortoises. Terrapin may refer to small semi-aquatic turtles that live in fresh and brackish water, in particular the diamondback terrapin. Although the members of the genus Terrapene dwell on land, they are referred to as box turtles rather than tortoises.
The American Society of Ichthyologists and Herpetologists uses "turtle" to describe all species of the order Testudines, regardless of whether they are land-dwelling or sea-dwelling, uses "tortoise" as a more specific term for slow-moving terrestrial species. In the United Kingdom, the word turtle is used for water-dwelling species, including ones known in the US as terrapins, but not for terrestrial species, which are known only as tortoises; the word chelonian is popular among veterinarians and conservationists working with these animals as a catch-all name for any member of the superorder Chelonia, which includes all turtles living and extinct, as well as their immediate ancestors. Chelonia is based on the Greek word for χελώνη chelone. Testudines, on the other hand, is based on the Latin word for testudo. Terrapin comes from an Algonquian word for turtle; some languages do not have this distinction. For example, in Spanish, the word tortuga is used for turtles and terrapins. A sea-dwelling turtle is tortuga marina, a freshwater species tortuga de río, a tortoise tortuga terrestre.
The largest living chelonian is the leatherback sea turtle, which reaches a shell length of 200 cm and can reach a weight of over 900 kg. Freshwater turtles are smaller, but with the largest species, the Asian softshell turtle Pelochelys cantorii, a few individuals have been reported up to 200 cm; this dwarfs the better-known alligator snapping turtle, the largest chelonian in North America, which attains a shell length of up to 80 cm and weighs as much as 113.4 kg. Giant tortoises of the genera Geochelone and others were widely distributed around the world into prehistoric times, are known to have existed in North and South America and Africa, they became extinct at the same time as the appearance of man, it is assumed humans hunted them for food. The only surviving giant tortoises are on the Seychelles and Galápagos Islands and can grow to over 130 cm in length, weigh about 300 kg; the largest chelonian was Archelon ischyros, a Late Cretaceous sea turtle known to have been up to 4.6 m long.
The smallest turtle is the speckled padloper tortoise of South Africa. It weighs about 140 g. Two other species of small turtles are the American mud turtles and musk turtles that live in an area that ranges from Canada to South America; the shell length of many species in this group is less than 13 cm in length. Turtles are divided according to how they retract their necks into their shells; the mechanism of neck retraction differs phylogenetically: the suborder Pleurodira retracts laterally to the side, anterior to shoulder girdles, while the suborder Cryptodira retracts straight back, between shoulder girdles. These motions are due to the morphology and arrangement of cervical vertebrae. Of all recent turtles, the cervical column consists of nine joints and eight vertebrae, which are individually independent. Since these vertebrae are not fused and are rounded, the neck is more flexible, being able to bend in the backwards and sideways directions; the primary function and evolutionary implicastion of neck retraction is thought to
Benjamin Waterhouse Hawkins
Benjamin Waterhouse Hawkins was an English sculptor and natural history artist renowned for his work on the life-size models of dinosaurs in the Crystal Palace Park in south London. The models made using the latest scientific knowledge, created a sensation at the time. Hawkins was a noted lecturer on zoological topics. Benjamin Waterhouse Hawkins was born in Bloomsbury, London on 8 February 1807, the son of Thomas Hawkins, an artist, Louisa Anne Waterhouse, the daughter of a Jamaica plantation family of apparent Catholic sympathies, he studied at St. Aloysius College, learned sculpture from William Behnes. At the age of 20, he began to study natural history and geology, he contributed illustrations to The Zoology of the Voyage of HMS Beagle. During the 1840s, he produced studies of living animals in Knowsley Park, near Liverpool for Edward Stanley, 13th Earl of Derby; the park was one of the largest private menageries in Victorian England and Hawkins' work was published with John Edward Gray's text as "Gleanings from the Menagerie at Knowsley".
Over the same period Hawkins exhibited four sculptures at the Royal Academy between 1847 and 1849, was elected a member of the Society of Arts in 1846 and a fellow of the Linnean Society in 1847. Fellowship of the Geological Society of London followed in 1854. Meanwhile due to Derby's connections, Hawkins was appointed assistant superintendent of the Great Exhibition of 1851 in London; the following year, he was appointed by the Crystal Palace company to create 33 life-size concrete models of extinct dinosaurs to be placed in the south London park to which the great glass exhibition hall was to be relocated. In this work, which took some three years, he collaborated with Sir Richard Owen and other leading scientific figures of the time: Owen estimated the size and overall shape of the animals, leaving Hawkins to sculpt the models according to Owen's directions. A dinner was held inside the mold used to make the Iguanodon; the dinner party, hosted by Owen on 31 December 1853, garnered attention in the press.
Most of the sculptures are still on display in Crystal Palace Park. In 1868, he traveled to the United States to deliver a series of lectures. Working with the scientist Joseph Leidy, Hawkins designed and cast an complete skeleton of Hadrosaurus foulkii, displayed at the Academy of Natural Sciences in Philadelphia. Supported on an iron framework in a lifelike pose, this was the world's first mounted dinosaur skeleton. Hawkins was commissioned to produce models for New York City's Central Park museum similar to these he had created in Sydenham, he established a studio on the original site of the American Museum of Natural History in Manhattan, planned to create a Paleozoic Museum. However, the project was shelved in 1870, the models that Hawkins had created were said to have been buried in the south part of Central Park. Hawkins turned to dinosaur skeleton reconstruction work at the Smithsonian Institution in Washington, he returned to England in 1874, but immediately returned, doing dinosaur reconstructions at Princeton University in Princeton, New Jersey.
These paintings remain in the collection of the Princeton University Art Museum. Hawkins worked at the Centennial Exhibition of 1876 in Philadelphia, he again returned to Britain in 1878. Hawkins had married in 1826 to Mary Selina Green, by her had several children. In 1835, he met and fell in love with artist Frances'Louisa' Keenan, the next year he left his family and bigamously married her, he lived with Louisa, having two additional daughters. On his 1874 return to England, he seems to have become estranged from Louisa, he was living with his son by Mary, amidst what he described a "climax of domestic troubles" thought to indicate that Louisa had learned that their 38-year marriage had been invalid, this may have led to his precipitous return to America in 1875. After his second return, he moved to West Brompton to be near his first wife, ill. Mary died in 1880. In 1883, Hawkins again married Louisa, although since they were not cohabitants at the time this was done for legalistic reasons, they never reconciled before her death the next year.
Hawkins suffered a debilitating stroke in 1889, leading to erroneous reports of his death, died on 27 January 1894. Robert J. Sawyer's 1994 novel End of an Era mentions the famous New Year's Eve 1853 dinner party inside the Iguanodon, citing both Hawkins and Sir Richard Owen by name. Comparative anatomy as applied to the purposes of the artist by Benjamin Waterhouse Hawkins and George Wallis. Published by Winsor & Newton, Ltd. Fauna boreali-americana, or, The zoology of the northern parts of British America: containing descriptions of the objects of natural history collected on the late northern land expeditions under command of Captain Sir John Franklin, R. N. by: Sir John Richardson, Charles M Curtis, Sir John Franklin, Benjamin Waterhouse Hawkins, William Kirby, Thomas Landseer, James de Carle Sowerby, William Swainson, Charles Edward Wagstaff. Published by John Murray Gleanings from the menagerie and aviary at Knowsley Hall by John Edward Gray, Benjamin Waterhouse Hawkins, Edward Lear. Published by Knowsley Princeton University Art Museum McCarthy, Steve.
The Crystal Palace Dinosaurs. Crystal Palace Foundation. Bramwell and Peck, Robert M. All in the Bones: A Biography of Benjamin Waterhouse Hawkins. Academy of Natural Sciences, 2008 Kerley, Barbara; the Dinosaurs of Waterh
Parareptilia is a subclass or clade of reptiles, variously defined as an extinct group of primitive anapsids, or a more cladistically correct alternative to Anapsida. Whether the term is valid depends on the phylogenetic position of turtles, whose relationships to other reptilian groups are still uncertain; the name Parareptilia was coined by Olson in 1947 to refer to an extinct group of Paleozoic reptiles, as opposed to the rest of the reptiles or Eureptilia. The name fell into disuse until it was revived by cladistic studies, to refer to those anapsids that were thought to be unrelated to turtles. Gauthier et al. 1988 provided the first phylogenetic definitions for the names of many amniote taxa and argued that captorhinids and turtles were sister groups, constituting the clade Anapsida. A name had to be found for various Permian and Triassic reptiles no longer included in the anapsids, "parareptiles" was chosen. However, they did not feel confident enough to erect Parareptilia as a formal taxon.
Their cladogram was as follows: Laurin and Reisz 1995 found a different cladogram, in which Reptilia were divided into Parareptilia and Eureptilia. Captorhinidae was transferred to Eureptilia, Parareptilia included both early anapsid reptiles and turtles; the mesosaurs were placed as the sister group to the reptiles. The traditional group Anapsida was rejected as paraphyletic; this gave the following result: In contrast, Rieppel, 1994, 1995. The diapsid affinities of turtles have been supported by molecular phylogenies; the first genome-wide phylogenetic analysis was completed by Wang et al.. Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the team used the largest turtle data set to date in their analysis and concluded that turtles are a sister group of crocodilians and birds; this placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics as it now possesses an anapsid skull. This would make Parareptilia a extinct group with skull features that coincidentally resemble those of turtles.
The cladogram below follows an analysis by M. S. Lee, in 2013. Benton, M. J.. Vertebrate Palaeontology. London: Blackwell Science Ltd. ISBN 978-0-632-05614-9. 3rd ed. 2004 ISBN 0-632-05637-1 deBraga, M.. "Reptile phylogeny and the interrelationships of turtles". Zoological Journal of the Linnean Society. 120: 281–354. Doi:10.1006/zjls.1997.0079. DeBraga, M.. "The Early Permian reptile Acleistorhinus pteroticus and its phylogenetic position". Journal of Vertebrate Paleontology. 16: 384–395. Doi:10.1080/02724634.1996.10011328. Gauthier, J.. "The early evolution of the Amniota". In M. J. Benton; the phylogeny and classification of the tetrapods, Volume 1: amphibians, birds. 103-155. Oxford: Clarendon Press. CS1 maint: Extra text: editors list Iwabe, N.. "Sister group relationship of turtles to the bird-crocodilian clade revealed by nuclear DNA-coded proteins". Molecular Biology and Evolution. 22: 810–813. Doi:10.1093/molbev/msi075. PMID 15625185. Retrieved 2010-12-31. Katsu, Y.. "From reptilian phylogenomics to reptilian genomes: analyses of c-Jun and DJ-1 proto-oncogenes".
Cytogenetic and Genome Research. 127: 79–93. Doi:10.1159/000297715. PMID 20234127. CS1 maint: Multiple names: authors list Laurin, M.. A.. "Phylogeny and Classification of Amniotes". at the Tree of Life Web Project. Laurin, M.. "A reevaluation of early amniote phylogeny". Zoological Journal of the Linnean Society. 113: 165–223. Doi:10.1111/j.1096-3642.1995.tb00932.x. Olson, E. C.. "The family Diadectidae and its bearing on the classification of reptiles". Fieldiana Geology. 11: 1–53. ISSN 0096-2651. Rieppel, O.. "Osteology of Simosaurus gaillardoti and the relationships of stem-group sauropterygia". Fieldiana Geology. 1462: 1–85. ISSN 0096-2651. Rieppel, O.. "Studies on skeleton formation in reptiles: implications for turtle relationships". Zoology-Analysis of Complex Systems. 98: 298–308. Rieppel, O.. "Turtles as diapsid reptiles". Nature. 384: 453–455. Doi:10.1038/384453a0. Romer, A. S.. Vertebrate Paleontology. Chicago: University of Chicago Press. ISBN 978-0-7167-1822-2. Roos, Jonas. "Extended mitogenomic phylogenetic analyses yield new insight into crocodylian evolution and their survival of the Cretaceous–Tertiary boundary".
Molecular Phylogenetics and Evolution. 45: 663–673. Doi:10.1016/j.ympev.2007.06.018. PMID 17719245. CS1 maint: Multiple names: authors list Zardoya, R.. "Complete mitochondrial genome suggests diapsid affinities of turtles". Proc Natl Acad Sci U S A. 95: 14226–14231. Doi:10.1073/pnas.95.24.14226. ISSN 0027-8424. PMC 24355. PMID 9826682. Parareptilia re Reptilian Subclass Parareptilia? - Dinosaur Mailing List archives
The red-eared slider known as the red-eared terrapin, is a semiaquatic turtle belonging to the family Emydidae. It is a subspecies of the pond slider, it is the most popular pet turtle in the United States and is popular as a pet in the rest of the world. It has, become the most traded turtle in the world, it is native to the southern United States and northern Mexico, but has become established in other places because of pet releases, has become an invasive species in many areas, where it outcompetes native species. The red-eared slider is included in the list of the world's 100 most invasive species published by the IUCN; the red-eared slider gets its name from the small red stripe around its ears and from its ability to slide off rocks and logs into the water. This species was known as Troost's turtle in honor of an American herpetologist Gerard Troost. Trachemys scripta troostii is now the scientific name for the Cumberland slider; the red-eared slider belongs to the order Testudines. It is a subspecies of Trachemys scripta.
It was classified under the name Chrysemys scripta elegans. The species Trachemys scripta contains three subspecies: T. s. elegans, T. s. scripta, T. s. troostii. The carapace of this species can reach more than 40 cm in length, but the average length ranges from 15 to 20 cm; the females of the species are larger than the males. They live between 20 and 30 years, although some individuals have lived for more than 40 years, their life expectancy is shorter. The quality of their living environment has a strong influence on their lifespans and well being; these turtles are poikilotherms, meaning they are unable to regulate their body temperatures independently. For this reason, they need to sunbathe to warm themselves and maintain their body temperatures; the shell is divided into two sections: the upper or dorsal carapace, the lower, ventral carapace or plastron. The upper carapace consists of the vertebral scutes, which form the elevated portion; the rear marginal scutes are notched. The scutes are bony keratinous elements.
The carapace is oval and flattened and has a weak keel, more pronounced in the young. The color of the carapace changes depending on the age of the turtle; the carapace has a dark green background with light and dark variable markings. In young or hatched turtles, it is leaf green and gets darker as a turtle gets older, until it is a dark green, turns a shade between brown and olive green; the plastron is always a light yellow with dark, irregular markings in the centre of most scutes. The plastron is variable in pattern; the head and tail are green with fine, yellow lines. The whole shell markings that aid in camouflaging an individual. Turtles have a complete skeletal system, with webbed feet that help them to swim and that can be withdrawn inside the carapace along with the head and tail; the red stripe on each side of the head distinguishes the red-eared slider from all other North American species and gives this species its name, as the stripe is located behind the eyes where their ears would be.
These stripes may lose their color over time. Some individuals can have a small mark of the same color on the top of their heads; the red-eared slider does not have an external auditory canal. The main internal organs of these reptiles are the lungs, stomach, liver and the urinary bladder. A cloaca serves both excretory and reproductive functions; some dimorphism exists between females. Red-eared slider young look identical regardless of their sex, making it difficult to distinguish them. One useful method, however, is to inspect the markings under their carapace, which fade as the turtles age, it is much easier to distinguish the sex of adults, as the shells of mature males are smaller than those of females. Male red-eared sliders reach sexual maturity when their carapaces' diameters measure 10 cm and females reach maturity when their carapaces measure 15 cm. Both male and females reach sexual maturity at five to six years; the male is smaller than the female, although this parameter is sometimes difficult to apply as individuals being compared could be of different ages.
Males have longer claws on their front feet than the females. The male's tail is thicker and longer; the cloacal opening of the female is at or under the rear edge of the carapace, while the male's opening occurs beyond the edge of the carapace. The male's plastron is concave, while that of the female is flat; the male's concave plastron helps to stabilize the male on the female's carapace during mating. Older males can sometimes have a dark greyish-olive green melanistic coloration, with subdued markings; the red stripe on the sides of the head may be difficult to be absent. The female's appearance is the same throughout her life; the red-eared slider originated from the area around the Mississippi River and the Gulf of Mexico, in warm climates in the southeastern United States. Their native
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is important where the descendant group is differentiated by gross anatomy and mode of living from the ancestral group; these fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is no way to know how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are used as models for such ancestors. In 1859, when Charles Darwin's On the Origin of Species was first published, the fossil record was poorly known. Darwin described the perceived lack of transitional fossils as, "... the most obvious and gravest objection which can be urged against my theory," but explained it by relating it to the extreme imperfection of the geological record.
He noted the limited collections available at that time, but described the available information as showing patterns that followed from his theory of descent with modification through natural selection. Indeed, Archaeopteryx was discovered just two years in 1861, represents a classic transitional form between earlier, non-avian dinosaurs and birds. Many more transitional fossils have been discovered since and there is now abundant evidence of how all classes of vertebrates are related, including many transitional fossils. Specific examples of class-level transitions are: tetrapods and fish and dinosaurs, mammals and "mammal-like reptiles"; the term "missing link" has been used extensively in popular writings on human evolution to refer to a perceived gap in the hominid evolutionary record. It is most used to refer to any new transitional fossil finds. Scientists, however, do not use the term. In evolutionary taxonomy, the prevailing form of taxonomy during much of the 20th century and still used in non-specialist textbooks, taxa based on morphological similarity are drawn as "bubbles" or "spindles" branching off from each other, forming evolutionary trees.
Transitional forms are seen as falling between the various groups in terms of anatomy, having a mixture of characteristics from inside and outside the newly branched clade. With the establishment of cladistics in the 1990s, relationships came to be expressed in cladograms that illustrate the branching of the evolutionary lineages in stick-like figures; the different so-called "natural" or "monophyletic" groups form nested units, only these are given phylogenetic names. While in traditional classification tetrapods and fish are seen as two different groups, phylogenetically tetrapods are considered a branch of fish. Thus, with cladistics there is no longer a transition between established groups, the term "transitional fossils" is a misnomer. Differentiation occurs within groups, represented as branches in the cladogram. In a cladistic context, transitional organisms can be seen as representing early examples of a branch, where not all of the traits typical of the known descendants on that branch have yet evolved.
Such early representatives of a group are termed "basal taxa" or "sister taxa," depending on whether the fossil organism belongs to the daughter clade or not. A source of confusion is the notion that a transitional form between two different taxonomic groups must be a direct ancestor of one or both groups; the difficulty is exacerbated by the fact that one of the goals of evolutionary taxonomy is to identify taxa that were ancestors of other taxa. However, it is impossible to be sure that any form represented in the fossil record is a direct ancestor of any other. In fact, because evolution is a branching process that produces a complex bush pattern of related species rather than a linear process producing a ladder-like progression, because of the incompleteness of the fossil record, it is unlikely that any particular form represented in the fossil record is a direct ancestor of any other. Cladistics deemphasizes the concept of one taxonomic group being an ancestor of another, instead emphasizes the identification of sister taxa that share a more recent common ancestor with one another than they do with other groups.
There are a few exceptional cases, such as some marine plankton microfossils, where the fossil record is complete enough to suggest with confidence that certain fossils represent a population, ancestral to a population of a different species. But, in general, transitional fossils are considered to have features that illustrate the transitional anatomical features of actual common ancestors of different taxa, rather than to be actual ancestors. Archaeopteryx is a genus of theropod dinosaur related to the birds. Since the late 19th century, it has been accepted by palaeontologists, celebrated in lay reference works, as being the oldest known bird, though a study in 2011 has cast doubt on this assessment, suggesting instead that it is a non-avialan dinosaur related to the origin of birds, it lived in what is now southern Germany in the Late Jurassic period around 150 million years ago, when Europe was an archipelago in a shallow warm tropical sea, much closer to the equator than it is now. Similar in shape to a European magpie, with the largest individuals attaining the size of a raven, Archaeopteryx could grow to about 0.5 metres in length.
Despite its small size, broad wings, inferred ability to fly or glide, Archaeopteryx has more in common with other small Mesozoic dinosaurs than it does with modern birds. In particular, it sh
Diapsids are a group of amniote tetrapods that developed two holes in each side of their skulls about 300 million years ago during the late Carboniferous period. The diapsids are diverse, include all crocodiles, snakes, tuatara and birds. Although some diapsids have lost either one hole, or both holes, or have a restructured skull, they are still classified as diapsids based on their ancestry. At least 7,925 species of diapsid reptiles exist in environments around the world today; the name Diapsida means "two arches", diapsids are traditionally classified based on their two ancestral skull openings posteriorly above and below the eye. This arrangement allows for the attachment of larger, stronger jaw muscles, enables the jaw to open more widely. A more obscure ancestral characteristic is a long lower arm bone compared to the upper arm bone. Diapsids were classified as one of four subclasses of the class Reptilia, all of which were based on the number and arrangement of openings in the skull; the other three subclasses were Synapsida and Euryapsida.
With the advent of phylogenetic nomenclature, this system of classification was modified. Today, the synapsids are not considered true reptiles, while Euryapsida were found to be an unnatural assemblage of diapsids that had lost one of their skull openings. Genetic studies and the discovery of the Triassic Pappochelys have shown that this is the case in turtles, which are heavily modified diapsids. In phylogenetic systems, birds are considered to be members of this group; some modern studies of reptile relationships have preferred to use the name "diapsid" to refer to the crown group of all modern diapsid reptiles but not their extinct relatives. However, many researchers have favored a more traditional definition that includes the prehistoric araeoscelidians. In 1991, Laurin defined Diapsida as a clade, "the most recent common ancestor of araeoscelidians and archosaurs, all its descendants". A cladistic analysis by Laurin and Piñeiro recovers Parareptilia as part of Diapsida, with pareiasaurs, turtles and procolophinoids recovered as more derived than the stem-diapsid Younginia.
Below is a cladogram showing the relations of the major groups of diapsids. Cladogram after Bickelmann et al. 2009 and Reisz et al. 2011: Vertebrate paleontology Synapsida Anapsida Euryapsida Data related to Diapsid at Wikispecies Diapsida. Michel Laurin and Jacques A. Gauthier. Tree of Life Web Project. June 22, 2000. Diapsida Cladogram at Mikko's Phylogeny Archive