Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago, although the exact origin and timing of the evolution of dinosaurs is the subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Reverse genetic engineering and the fossil record both demonstrate that birds are modern feathered dinosaurs, having evolved from earlier theropods during the late Jurassic Period; as such, birds were the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event 66 million years ago. Dinosaurs can therefore be divided into birds; this article deals with non-avian dinosaurs. Dinosaurs are a varied group of animals from taxonomic and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish. Using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs.
Dinosaurs are represented on every continent by fossil remains. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded. Most research conducted since the 1970s, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction; some were herbivorous, others carnivorous. Evidence suggests that egg-laying and nest-building are additional traits shared by all dinosaurs and non-avian alike. While dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, some extinct groups developed skeletal modifications such as bony armor and spines. While the dinosaurs' modern-day surviving avian lineage are small due to the constraints of flight, many prehistoric dinosaurs were large-bodied—the largest sauropod dinosaurs are estimated to have reached lengths of 39.7 meters and heights of 18 meters and were the largest land animals of all time.
Still, the idea that non-avian dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large, sturdy bones are more to last until they are fossilized. Many dinosaurs were quite small: Xixianykus, for example, was only about 50 cm long. Since the first dinosaur fossils were recognized in the early 19th century, mounted fossil dinosaur skeletons have been major attractions at museums around the world, dinosaurs have become an enduring part of world culture; the large sizes of some dinosaur groups, as well as their monstrous and fantastic nature, have ensured dinosaurs' regular appearance in best-selling books and films, such as Jurassic Park. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, new discoveries are covered by the media; the taxon'Dinosauria' was formally named in 1841 by paleontologist Sir Richard Owen, who used it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were being recognized in England and around the world.
The term is derived from Ancient Greek δεινός, meaning'terrible, potent or fearfully great', σαῦρος, meaning'lizard or reptile'. Though the taxonomic name has been interpreted as a reference to dinosaurs' teeth and other fearsome characteristics, Owen intended it to evoke their size and majesty. Other prehistoric animals, including pterosaurs, ichthyosaurs and Dimetrodon, while popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs. Pterosaurs are distantly related to dinosaurs; the other groups mentioned are, like dinosaurs and pterosaurs, members of Sauropsida, except Dimetrodon. Under phylogenetic nomenclature, dinosaurs are defined as the group consisting of the most recent common ancestor of Triceratops and Neornithes, all its descendants, it has been suggested that Dinosauria be defined with respect to the MRCA of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria. Both definitions result in the same set of animals being defined as dinosaurs: "Dinosauria = Ornithischia + Saurischia", encompassing ankylosaurians, ceratopsians, ornithopods and sauropodomorphs.
Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a separate class that had evolved from dinosaurs, a distinct superorder. However, a majority of contemporary paleontologists concerned with dinosaurs reject the traditional style of classification in favor of phylogenetic taxonomy. Birds are thus considered to be dinosaurs and dinosaurs are, not extinct. Birds are classified as belonging to the subgroup M
Cladistics is an approach to biological classification in which organisms are categorized in groups based on the most recent common ancestor. Hypothesized relationships are based on shared derived characteristics that can be traced to the most recent common ancestor and are not present in more distant groups and ancestors. A key feature of a clade is that all its descendants are part of the clade. All descendants stay in their overarching ancestral clade. For example, if within a strict cladistic framework the terms animals, bilateria/worms, fishes/vertebrata, or monkeys/anthropoidea were used, these terms would include humans. Many of these terms are used paraphyletically, outside of cladistics, e.g. as a'grade'. Radiation results in the generation of new subclades by bifurcation; the techniques and nomenclature of cladistics have been applied to other disciplines. Cladistics is now the most used method to classify organisms; the original methods used in cladistic analysis and the school of taxonomy derived from the work of the German entomologist Willi Hennig, who referred to it as phylogenetic systematics.
Cladistics in the original sense refers to a particular set of methods used in phylogenetic analysis, although it is now sometimes used to refer to the whole field. What is now called the cladistic method appeared as early as 1901 with a work by Peter Chalmers Mitchell for birds and subsequently by Robert John Tillyard in 1921, W. Zimmermann in 1943; the term "clade" was introduced in 1958 by Julian Huxley after having been coined by Lucien Cuénot in 1940, "cladogenesis" in 1958, "cladistic" by Cain and Harrison in 1960, "cladist" by Mayr in 1965, "cladistics" in 1966. Hennig referred to his own approach as "phylogenetic systematics". From the time of his original formulation until the end of the 1970s, cladistics competed as an analytical and philosophical approach to systematics with phenetics and so-called evolutionary taxonomy. Phenetics was championed at this time by the numerical taxonomists Peter Sneath and Robert Sokal, evolutionary taxonomy by Ernst Mayr. Conceived, if only in essence, by Willi Hennig in a book published in 1950, cladistics did not flourish until its translation into English in 1966.
Today, cladistics is the most popular method for constructing phylogenies from morphological data. In the 1990s, the development of effective polymerase chain reaction techniques allowed the application of cladistic methods to biochemical and molecular genetic traits of organisms, vastly expanding the amount of data available for phylogenetics. At the same time, cladistics became popular in evolutionary biology, because computers made it possible to process large quantities of data about organisms and their characteristics; the cladistic method interprets each character state transformation implied by the distribution of shared character states among taxa as a potential piece of evidence for grouping. The outcome of a cladistic analysis is a cladogram – a tree-shaped diagram, interpreted to represent the best hypothesis of phylogenetic relationships. Although traditionally such cladograms were generated on the basis of morphological characters and calculated by hand, genetic sequencing data and computational phylogenetics are now used in phylogenetic analyses, the parsimony criterion has been abandoned by many phylogeneticists in favor of more "sophisticated" but less parsimonious evolutionary models of character state transformation.
Cladists contend. Every cladogram is based on a particular dataset analyzed with a particular method. Datasets are tables consisting of molecular, ethological and/or other characters and a list of operational taxonomic units, which may be genes, populations, species, or larger taxa that are presumed to be monophyletic and therefore to form, all together, one large clade. Different datasets and different methods, not to mention violations of the mentioned assumptions result in different cladograms. Only scientific investigation can show, more to be correct; until for example, cladograms like the following have been accepted as accurate representations of the ancestral relations among turtles, lizards and birds: If this phylogenetic hypothesis is correct the last common ancestor of turtles and birds, at the branch near the ▼ lived earlier than the last common ancestor of lizards and birds, near the ♦. Most molecular evidence, produces cladograms more like this: If this is accurate the last common ancestor of turtles and birds lived than the last common ancestor of lizards and birds.
Since the cladograms provide competing accounts of real events, at most one of them is correct. The cladogram to the right represents the current universally accepted hypothesis that all primates, including strepsirrhines like the lemurs and lorises, had a common ancestor all of whose descendants were primates, so form a clade. Within the primates, all anthropoids are hypothesized to have had a common ancestor all of whose descendants were anthropoids, so they form the clade called Anthropoidea; the "prosimians", on the other hand, form a paraphyletic taxon. The name Prosimii is not used in phylogenetic nomenclature, whic
University of California
The University of California is a public university system in the U. S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-system public higher education plan, which includes the California State University system and the California Community Colleges System; the University of California was founded on March 23, 1868, operated temporarily in Oakland before moving to its new campus in Berkeley in 1873. In March 1951, the University of California began to reorganize itself into something distinct from its first campus at Berkeley, with Robert Gordon Sproul remaining in place as the first systemwide President and Clark Kerr becoming the first Chancellor of UC Berkeley. However, the 1951 reorganization was stalled by resistance from Sproul and his allies, it was not until Kerr succeeded Sproul as President that UC was able to evolve into a true university system from 1957 to 1960. In the 21st century, the University of California has 10 campuses, a combined student body of 251,700 students, 21,200 faculty members, 144,000 staff members and over 1.86 million living alumni, as governed by a semi-autonomous Board of Regents.
Its tenth and newest campus in Merced opened in fall 2005. Nine campuses enroll graduate students. In addition, the UC Hastings College of Law, located in San Francisco, is affiliated with UC, but other than sharing its name is autonomous from the rest of the system; the University of California manages or co-manages three national laboratories for the U. S. Department of Energy: Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, Los Alamos National Laboratory. Collectively, the colleges and alumni of the University of California make it the most comprehensive and advanced postsecondary educational system in the world, responsible for nearly $50 billion per year of economic impact. UC campuses have large numbers of distinguished faculty in every academic discipline, with UC faculty and researchers having won at least 62 Nobel Prizes as of 2017. In 1849, the state of California ratified its first constitution, which contained the express objective of creating a complete educational system including a state university.
Taking advantage of the Morrill Land-Grant Acts, the California Legislature established an Agricultural and Mechanical Arts College in 1866. However, it existed only as a placeholder to secure federal land-grant funds. Meanwhile, Congregational minister Henry Durant, an alumnus of Yale, had established the private Contra Costa Academy, on June 20, 1853, in Oakland, California; the initial site was bounded by Twelfth and Fourteenth Streets and Harrison and Franklin Streets in downtown Oakland. In turn, the Academy's trustees were granted a charter in 1855 for a College of California, though the College continued to operate as a college preparatory school until it added college-level courses in 1860; the College's trustees and supporters believed in the importance of a liberal arts education, but ran into a lack of interest in liberal arts colleges on the American frontier. In November 1857, the College's trustees began to acquire various parcels of land facing the Golden Gate in what is now Berkeley for a future planned campus outside of Oakland.
But first, they needed to secure the College's water rights by buying a large farm to the east. In 1864, they organized the College Homestead Association, which borrowed $35,000 to purchase the land, plus another $33,000 to purchase 160 acres of land to the south of the future campus; the Association subdivided the latter parcel and started selling lots with the hope it could raise enough money to repay its lenders and create a new college town. But sales of new homesteads fell short. Governor Frederick Low favored the establishment of a state university based upon the University of Michigan plan, thus in one sense may be regarded as the founder of the University of California. At the College of California's 1867 commencement exercises, where Low was present, Benjamin Silliman, Jr. criticized Californians for creating a state polytechnic school instead of a real university. That same day, Low first suggested a merger of the already-functional College of California with the nonfunctional state college, went on to participate in the ensuing negotiations.
On October 9, 1867, the College's trustees reluctantly agreed to join forces with the state college to their mutual advantage, but under one condition—that there not be an "Agricultural and Mechanical Arts College", but a complete university, within which the assets of the College of California would be used to create a College of Letters. Accordingly, the Organic Act, establishing the University of California, was introduced as a bill by Assemblyman John W. Dwinelle on March 5, 1868, after it was duly passed by both houses of the state legislature, it was signed into state law by Governor Henry H. Haight on March 23, 1868. However, as constituted, the new University was not an actual merger of the two colleges, but was an new institution which inherited certain objectives and assets from each of them; the University
Système universitaire de documentation
The système universitaire de documentation or SUDOC is a system used by the libraries of French universities and higher education establishments to identify and manage the documents in their possession. The catalog, which contains more than 10 million references, allows students and researcher to search for bibliographical and location information in over 3,400 documentation centers, it is maintained by the Bibliographic Agency for Higher Education. Official website
Night lizards are a group of small scincomorph lizards, averaging from less than 4 cm to over 12 cm snout-vent length. Most species are viviparous, with the exception of those in the genus Cricosaura; the family has only three living genera, with 34 living species. The genera are divided by geographic range: Xantusia in southwestern North America and Baja California, Cricosaura in Cuba, Lepidophyma, the most populous night lizard genus, in Central America. Three fossil genera are known: Catactegenys, Palaeoxantusia. Night lizards were thought to be nocturnal because of their secretive lifestyle, but they are in fact diurnal. Night lizards have evolved to live in narrow environmental niches—"microhabitat specialization"—such as rock crevices or damp logs, may spend their entire life under the same cover. Physically, night lizards are characterized by flat bodies and heads, their heads are covered by smooth plates, while their bodies have rougher, granular skin. Their eyes, like those of snakes, are covered by immoveable, transparent membranes that function as eyelids.
They feed on insects and sometimes plants. Contrary to the reproductive strategies of most small lizards, night lizards tend to have low reproductive rates, with several species giving birth to only one or two offspring, after a gestation period of about three months, they take several years to reach sexual maturity. However, the covert lifestyle of night lizards has contributed to a high life expectancy. FAMILY XANTUSIIDAE Subfamily Cricosaurinae Genus Cricosaura - Cuban night lizard Subfamily Xantusiinae Genus Lepidophyma - Tropical night lizards Genus Xantusia - Typical night lizards xantusiidae
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