The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period, 298.9 Mya. The name Carboniferous means "coal-bearing" and derives from the Latin words carbō and ferō, was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern'system' names to be employed, reflects the fact that many coal beds were formed globally during that time; the Carboniferous is treated in North America as two geological periods, the earlier Mississippian and the Pennsylvanian. Terrestrial animal life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would evolve into amniotes, the first terrestrial vertebrates. Arthropods were very common, many were much larger than those of today. Vast swaths of forest covered the land, which would be laid down and become the coal beds characteristic of the Carboniferous stratigraphy evident today.
The atmospheric content of oxygen reached its highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. The half of the period experienced glaciations, low sea level, mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change. In the United States the Carboniferous is broken into Mississippian and Pennsylvanian subperiods; the Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal-bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal in duration. In Europe the Lower Carboniferous sub-system is known as the Dinantian, comprising the Tournaisian and Visean Series, dated at 362.5-332.9 Ma, the Upper Carboniferous sub-system is known as the Silesian, comprising the Namurian and Stephanian Series, dated at 332.9-298.9 Ma.
The Silesian is contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the Carboniferous Limestone, the Namurian as the Millstone Grit, the Westphalian as the Coal Measures and Pennant Sandstone; the International Commission on Stratigraphy faunal stages from youngest to oldest, together with some of their regional subdivisions, are: A global drop in sea level at the end of the Devonian reversed early in the Carboniferous. There was a drop in south polar temperatures; these conditions had little effect in the deep tropics, where lush swamps to become coal, flourished to within 30 degrees of the northernmost glaciers. Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites hard; this sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation.
The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe along the present line of eastern North America; this continental collision resulted in the Hercynian orogeny in Europe, the Alleghenian orogeny in North America. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural Mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China, South China continents were still separated from Laurasia; the Late Carboniferous Pangaea was shaped like an "O." There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and closed - Rheic Ocean, the small, shallow Ural Ocean and Proto-Tethys Ocean. Average global temperatures in the Early Carboniferous Period were high: 20 °C.
However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C. Lack of growth rings of fossilized trees suggest a lack of seasons of a tropical climate. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are referred to as Permo-Carboniferous in age; the cooling and drying of the climate led to the Carboniferous Rainforest Collapse during the late Carboniferous. Tropical rainforests fragmented and were devastated by climate change. Carboniferous rocks in Europe and eastern North America consist of a repeated sequence of limestone, sandstone and coal beds. In North America, the early Carboniferous is marine
Laos the Lao People's Democratic Republic referred to by its colloquial name of Muang Lao, is a socialist state and the only landlocked country in Southeast Asia. Located at the heart of the Indochinese peninsula, Laos is bordered by Myanmar and China to the northwest, Vietnam to the east, Cambodia to the southwest, Thailand to the west and southwest. Present-day Laos traces its historic and cultural identity to the kingdom of Lan Xang Hom Khao, which existed for four centuries as one of the largest kingdoms in Southeast Asia. Due to Lan Xang's central geographical location in Southeast Asia, the kingdom became a popular hub for overland trade, becoming wealthy economically as well as culturally. After a period of internal conflict, Lan Xang broke off into three separate kingdoms—Luang Phrabang and Champasak. In 1893, it became a French protectorate, with the three territories uniting to form what is now known as the country of Laos, it gained independence in 1945 after Japanese occupation, but was recolonised by France until it won autonomy in 1949.
Laos became independent with a constitutional monarchy under Sisavang Vong. Shortly after independence, a long civil war began, which saw the communist resistance, supported by the Soviet Union, fight against, the monarchy and a number of military dictatorships, supported by the United States. After the Vietnam War ended in 1975, the Communist Pathet Lao movement came to power, seeing the end to the civil war. During the first years of Communist rule, Laos was dependent on military and economic aid supported by the Soviet Union until its dissolution in 1991. In 2018, the country had the fourth highest GDP per capita in Indochina, after Singapore and Thailand. In the same year, the country ranked 139th on the Human Development Index, indicating medium development. Laos is a member of the Asia-Pacific Trade Agreement, Association of Southeast Asian Nations, East Asia Summit and La Francophonie. Laos applied for membership of the World Trade Organization in 1997, it is a one-party socialist republic espousing Marxism–Leninism governed by the Lao People's Revolutionary Party.
The capital and largest city is Vientiane. Other major cities include Luang Prabang and Pakse; the official language is Lao. Laos is a multi-ethnic country, with the politically and culturally dominant Lao people making up about 55 percent of the population in the lowlands. Mon-Khmer groups, the Hmong and other indigenous hill tribes, accounting for 45 percent of the population, live in the foothills and mountains. Laos's strategies for development are based on generating electricity from its rivers and selling the power to its neighbours, namely Thailand and Vietnam, as well as its initiative to become a "land-linked" nation, shown by the construction of four new railways connecting Laos to its neighbours. Laos has been referred to as one of East Asia and Pacific's Fastest Growing Economies by the World Bank, with annual GDP growth averaging 7.8% for the past decade. The English word Laos was coined by the French, who united the three Lao kingdoms in French Indochina in 1893 and named the country as the plural of the dominant and most common ethnic group, which are the Lao people.
In the Lao language, the country's name is "Muang Lao" or "Pathet Lao", both mean "Lao Country". An ancient human skull was recovered from the Tam Pa Ling Cave in the Annamite Mountains in northern Laos. Stone artifacts including Hoabinhian types have been found at sites dating to the Late Pleistocene in northern Laos. Archaeological evidence suggests agriculturist society developed during the 4th millennium BC. Burial jars and other kinds of sepulchers suggest a complex society in which bronze objects appeared around 1500 BC, iron tools were known from 700 BC; the proto-historic period is characterised by contact with Indian civilisations. According to linguistic and other historical evidence, Tai-speaking tribes migrated southwestward to the modern territories of Laos and Thailand from Guangxi sometime between the 8th–10th centuries. Laos traces its history to the kingdom of Lan Xang, founded in the 14th century by a Lao prince Fa Ngum, with 10,000 Khmer troops, took over Vientiane. Ngum was descended from a long line of Lao kings.
He made Theravada Buddhism Lan Xang prospered. Within 20 years of its formation, the kingdom expanded eastward to Champa and along the Annamite mountains in Vietnam, his ministers, unable to tolerate his ruthlessness, forced him into exile to the present-day Thai province of Nan in 1373, where he died. Fa Ngum's eldest son, Oun Heuan, ascended to the throne under the name Samsenthai and reigned for 43 years. Lan Xang became an important trade centre during Samsenthai's reign, but after his death in 1421 it collapsed into warring factions for 100 years. In 1520, Photisarath came to the throne and moved the capital from Luang Prabang to Vientiane to avoid a Burmese invasion. Setthathirat became king in 1548, after his father was killed, ordered the construction of what became the symbol of Laos, That Luang. Setthathirat disappeared in the mountains on his way back from a military expedition into Cambodia and Lan Xang began to decline, it was not until 1637, when Sou
The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the Pliocene; some geologists assert that the Neogene cannot be delineated from the modern geological period, the Quaternary. The term "Neogene" was coined in 1853 by the Austrian palaeontologist Moritz Hörnes. During this period and birds continued to evolve into modern forms, while other groups of life remained unchanged. Early hominids, the ancestors of humans, appeared in Africa near the end of the period; some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific to the Atlantic Ocean, leaving only the Gulf Stream to transfer heat to the Arctic Ocean; the global climate cooled over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows.
In ICS terminology, from upper to lower: The Pliocene Epoch is subdivided into 2 ages: Piacenzian Age, preceded by Zanclean AgeThe Miocene Epoch is subdivided into 6 ages: Messinian Age, preceded by Tortonian Age Serravallian Age Langhian Age Burdigalian Age Aquitanian AgeIn different geophysical regions of the world, other regional names are used for the same or overlapping ages and other timeline subdivisions. The terms Neogene System and upper Tertiary System describe the rocks deposited during the Neogene Period; the continents in the Neogene were close to their current positions. The Isthmus of Panama formed, connecting South America; the Indian subcontinent continued forming the Himalayas. Sea levels fell, creating land bridges between Africa and Eurasia and between Eurasia and North America; the global climate became seasonal and continued an overall drying and cooling trend which began at the start of the Paleogene. The ice caps on both poles began to grow and thicken, by the end of the period the first of a series of glaciations of the current Ice Age began.
Marine and continental flora and fauna have a modern appearance. The reptile group Choristodera became extinct in the early part of the period, while the amphibians known as Allocaudata disappeared at the end. Mammals and birds continued to be the dominant terrestrial vertebrates, took many forms as they adapted to various habitats; the first hominins, the ancestors of humans, may have appeared in southern Europe and migrated into Africa. In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones and grasslands replaced many forests. Grasses therefore diversified, herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses and bison. Eucalyptus fossil leaves occur in the Miocene of New Zealand, where the genus is not native today, but have been introduced from Australia; the Neogene traditionally ended at the end of the Pliocene Epoch, just before the older definition of the beginning of the Quaternary Period. However, there was a movement amongst geologists to include ongoing geological time in the Neogene, while others insist the Quaternary to be a separate period of distinctly different record.
The somewhat confusing terminology and disagreement amongst geologists on where to draw what hierarchical boundaries is due to the comparatively fine divisibility of time units as time approaches the present, due to geological preservation that causes the youngest sedimentary geological record to be preserved over a much larger area and to reflect many more environments than the older geological record. By dividing the Cenozoic Era into three periods instead of seven epochs, the periods are more comparable to the duration of periods in the Mesozoic and Paleozoic eras; the International Commission on Stratigraphy once proposed that the Quaternary be considered a sub-era of the Neogene, with a beginning date of 2.58 Ma, namely the start of the Gelasian Stage. In the 2004 proposal of the ICS, the Neogene would have consisted of the Miocene and Pliocene epochs; the International Union for Quaternary Research counterproposed that the Neogene and the Pliocene end at 2.58 Ma, that the Gelasian be transferred to the Pleistocene, the Quaternary be recognized as the third period in the Cenozoic, citing key changes in Earth's climate and biota that occurred 2.58 Ma and its correspondence to the Gauss-Matuyama magnetostratigraphic boundary.
In 2006 ICS and INQUA reached a compromise that made Quaternary a subera, subdividing Cenozoic into the old classical Tertiary and Quaternary, a compromise, rejected by International Union of Geological Sciences because it split both Neogene and Pliocene in two. Following formal discussions at the 2008 International Geological Congress in Oslo, the ICS decided in May 2009 to make the Quaternary the youngest period of the Cenozoic Era with its base at 2.58 Mya and including the Gelasian age, considered part of the Neogene Period and Pliocene Epoch. Thus the Neogene Period ends bounding the succeeding Quaternary Period at 2.58 Mya. "Digital Atlas of Neogene Life for the Southeastern United States". San Jose State University. Archived from the original on 2013-04-23. Retrieved 21 September 2018
The Jurassic period was a geologic period and system that spanned 56 million years from the end of the Triassic Period 201.3 million years ago to the beginning of the Cretaceous Period 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era known as the Age of Reptiles; the start of the period was marked by the major Triassic–Jurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian-Toarcian extinction in the Early Jurassic, the Tithonian event at the end; the Jurassic period is divided into three epochs: Early and Late. In stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, Upper Jurassic series of rock formations; the Jurassic is named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified. By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north, Gondwana to the south; this created more coastlines and shifted the continental climate from dry to humid, many of the arid deserts of the Triassic were replaced by lush rainforests.
On land, the fauna transitioned from the Triassic fauna, dominated by both dinosauromorph and crocodylomorph archosaurs, to one dominated by dinosaurs alone. The first birds appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life; the oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates. The chronostratigraphic term "Jurassic" is directly linked to the Jura Mountains, a mountain range following the course of the France–Switzerland border. During a tour of the region in 1795, Alexander von Humboldt recognized the limestone dominated mountain range of the Jura Mountains as a separate formation that had not been included in the established stratigraphic system defined by Abraham Gottlob Werner, he named it "Jura-Kalkstein" in 1799.
The name "Jura" is derived from the Celtic root *jor via Gaulish *iuris "wooded mountain", borrowed into Latin as a place name, evolved into Juria and Jura. The Jurassic period is divided into three epochs: Early and Late. In stratigraphy, the Jurassic is divided into the Lower Jurassic, Middle Jurassic, Upper Jurassic series of rock formations known as Lias and Malm in Europe; the separation of the term Jurassic into three sections originated with Leopold von Buch. The faunal stages from youngest to oldest are: During the early Jurassic period, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana; the Jurassic North Atlantic Ocean was narrow, while the South Atlantic did not open until the following Cretaceous period, when Gondwana itself rifted apart. The Tethys Sea closed, the Neotethys basin appeared. Climates were warm, with no evidence of a glacier having appeared; as in the Triassic, there was no land over either pole, no extensive ice caps existed.
The Jurassic geological record is good in western Europe, where extensive marine sequences indicate a time when much of that future landmass was submerged under shallow tropical seas. In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface. Though the epicontinental Sundance Sea left marine deposits in parts of the northern plains of the United States and Canada during the late Jurassic, most exposed sediments from this period are continental, such as the alluvial deposits of the Morrison Formation; the Jurassic was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. Carbonate hardgrounds were thus common, along with calcitic ooids, calcitic cements, invertebrate faunas with dominantly calcitic skeletons; the first of several massive batholiths were emplaced in the northern American cordillera beginning in the mid-Jurassic, marking the Nevadan orogeny. Important Jurassic exposures are found in Russia, South America, Japan and the United Kingdom.
In Africa, Early Jurassic strata are distributed in a similar fashion to Late Triassic beds, with more common outcrops in the south and less common fossil beds which are predominated by tracks to the north. As the Jurassic proceeded and more iconic groups of dinosaurs like sauropods and ornithopods proliferated in Africa. Middle Jurassic strata are neither well studied in Africa. Late Jurassic strata are poorly represented apart from the spectacular Tendaguru fauna in Tanzania; the Late Jurassic life of Tendaguru is similar to that found in western North America's Morrison Formation. During the Jurassic period, the primary vertebrates living in the sea were marine reptiles; the latter include ichthyosaurs, which were at the peak of their diversity, plesiosaurs and marine crocodiles of the families Teleosauridae and Metriorhynchidae. Numerous turtles could be found in rivers. In the invertebrate world, several new groups appeared, including rudists (a reef-formi
Huabeisaurus was a genus of dinosaur from the Late Cretaceous. It was a sauropod; the type species, Huabeisaurus allocotus, was first described by Pang Qiqing and Cheng Zhengwu in 2000. Huabeisaurus is known from numerous remains found in the 1990s, which include teeth, partial limbs and vertebrae. Due to its relative completeness, Huabeisaurus represents a significant taxon for understanding sauropod evolution in Asia. Huabeisaurus comes from Kangdailiang and Houyu, Zhaojiagou Town, Tianzhen County, Shanxi province, China; the holotype was found in the unnamed upper member of the Huiquanpu Formation, Late Cretaceous in age based on ostracods and fission-track dating. Huabeisaurus measures 20 metres long and 5 metres high, as estimated by Pang and Cheng in 2000, it would have been a quadrupedal herbivore with a long tail, like most other sauropods. The skeleton has been presumed to have belonged to an mature individual, because it lacks sutures on vertebrae, but not on pelvic material. A set of 12 characters were identified by D'Emic et al. in 2013 that differentiate Huabeisaurus from other sauropods.
An isolated humerus, designated the paratype by Pang and Cheng, comes from a locality over 200 meters away from the type locality of Huabeisaurus, in a fluvially deposited sandy conglomeratic layer in the lower member of the Huiquanpu Formation. This layer is 90 m lower stratigraphically than the type horizon of Huabeisaurus, which comes from the upper member of the Huiquanpu Formation; the humerus thus comes from a stratum representing a different and older depositional environment than that of Huabeisaurus, does not overlap anatomically with the holotypic skeleton, so cannot be referred it. The discoverers erected a new family for the genus, although this family name is not used amongst paleontologists; the family was again proposed, this time by D'Emic et al. because Euhelopodidae, which Huabeisaurus has been assigned to most might have to be split into smaller clades throughout Somphospondyli because of all the taxa assigned to it. Pang and Cheng tentatively suggested. One problem, however, is that the femora of Huabeisaurus and "T." falloti differ in the bevel of the distal end versus the long axis of the bone, so the two cannot represent the same genus.
The Late Cretaceous titanosauriform sauropod Huabeisaurus is known from teeth and much of the postcranial skeleton. Its completeness makes it an important taxon for integrating and interpreting anatomical observations from more fragmentary Cretaceous East Asian sauropods and for understanding titanosauriform evolution in general. Measuring 20 metres in total length, Huabeisaurus is large when compared to most dinosaurs, but by sauropod standards, it was only midsized, it had a hip height of 5 metres. Like other sauropods, it would have been a quadrupedal herbivore with a long tail; the skeleton has been presumed to have belonged to an mature individual. The absence of sutures between the neural arches and centra of cervical and caudal vertebrae suggests that the specimen was nearing sexual maturity, but the open sutures between the scapula and coracoid, the ilium and some sacral ribs suggest that it had not reached full maturity; the sauropod Huabeisaurus was excavated from Upper Cretaceous sediments of the province of Shanxi, in northeast China.
The skeleton was recovered in the 1990s. The holotype of Huabeisaurus is a articulated individual composed of teeth, dorsal and caudal vertebrae, complete pectoral and pelvic girdles, nearly complete limbs. Due to its relative completeness, Huabeisaurus represents a significant taxon for understanding sauropod evolution in Asia. Limb and girdle elements from the left and right sides of the body match each other in size and are the appropriate size to belong to the same individual as the vertebrae and ribs; the disposition of bones in the quarry is as expected if the animal were lying on its left side in an opisthotonic pose, but nearly all bones show some disorientation and disarticulation: the cervical vertebrae are arranged along a curved line, extending along this tight curve sit two of the dorsal vertebrae followed by the sacrum and caudal vertebrae. The sacrum and first three caudal vertebrae were found in articulation and in line with the remaining articulated caudal vertebrae. Twenty-seven caudal vertebrae are shown on the quarry map, but 30 were found in the collection, pre-restoration photos indicate that 32 were present.
Many of the chevrons were found articulated with their respective caudal vertebrae. The left and right scapulae were recovered on the left and right sides of the body, respectively; the left radius was found about midway between the pectoral girdle elements. Left and right femora and ilia were located close to one another and all of these were found near the sacrum; the sacrum is depicted with its left side facing upwards on the quarry map, but this might have been an error because the left side of the sacrum is damaged and the left ilium is missing. The elements of the left and right crura were found in close association. Dorsal rib fragments were scattered across the quarry area. In sum, some degree of dispositioning occurred to HBV-20001 before or during burial, resulting in loss and disarticulation of some elements, but the disposition, overall agreement in size, lack of duplication of bones su
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
Somphospondylans are an extinct clade of titanosauriform sauropods that lived throughout the world from the Late Jurassic through the Cretaceous in North America,South America,Europe,Asia and Australia. The group can be defined as "the most inclusive clade that includes Saltasaurus loricatus but excludes Brachiosaurus altithorax". Features found as diagnostic of this clade by Mannion et al. include the possession of at least 15 cervical vertebrae.