The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, where rocks from this period were first studied; the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods became well-established. Fish reached substantial diversity during this time, leading the Devonian to be dubbed the "Age of Fishes." The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating every known aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral and pelvic fins evolved into legs.
In the oceans, primitive sharks became more numerous than in the Late Ordovician. The first ammonites, species of molluscs, appeared. Trilobites, the mollusc-like brachiopods and the great coral reefs, were still common; the Late Devonian extinction which started about 375 million years ago affected marine life, killing off all placodermi, all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, the early formation of the small continent of Euramerica in between; the period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough.
Murchison and Sedgwick named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, to the beginning of the Carboniferous 358.9 Mya. In nineteenth-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian and Farlovian stages, the latter three of which are placed in the Devonian; the Devonian has erroneously been characterised as a "greenhouse age", due to sampling bias: most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America, which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid but in fact the climate in the Devonian differed during its epochs and between geographic regions.
For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, North America, China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common; the Devonian Period is formally broken into Early and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower and Upper parts of the Devonian System. Early DevonianThe Early Devonian lasted from 419.2 ± 2.8 to 393.3 ± 2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ± 2.8 to 407.6 ± 2.5, was followed by the Emsian, which lasted until the Middle Devonian began, 393.3± 2.7 million years ago. During this time, the first ammonoids appeared. Ammonoids during this time period differed little from their nautiloid counterparts; these ammonoids belong to the order Agoniatitida, which in epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida.
This class of cephalopod molluscs would dominate the marine fauna until the beginning of the Mesozoic era. Middle DevonianThe Middle Devonian comprised two subdivisions: first the Eifelian, which gave way to the Givetian 387.7± 2.7 million years ago. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments due to drastic environmental changes and due to the increasing competition and diversity of jawed fishes; the shallow, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided the environment necessary for certain early fish to develop such essential characteristics as well developed lungs, the ability to crawl out of the water and onto the land for short periods of time. Late DevonianFinally, the Late Devonian started with the Frasnian, 382.7 ± 2.8 to 372.2 ± 2.5, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivisi
Sauropodomorpha is an extinct clade of long-necked, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods grew to large sizes, had long necks and tails, were quadrupedal, became the largest animals to walk the Earth; the "prosauropods", which preceded the sauropods, were smaller and were able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic until their decline and extinction at the end of the Cretaceous. Sauropodomorphs were adapted to browsing higher than any other contemporary herbivore, giving them access to high tree foliage; this feeding strategy is supported by many of their defining characteristics, such as: a light, tiny skull on the end of a long neck and a counterbalancing long tail. Their teeth were weak, shaped like leaves or spoons. Instead of grinding teeth, they had stomach stones, similar to the gizzard stones of modern birds and crocodiles, to help digest tough plant fibers.
The front of the upper mouth bends down in. One of the earliest known sauropodomorphs, was small and slender; the largest sauropods, like Supersaurus, Diplodocus hallorum and Argentinosaurus, reached 30–40 metres in length, 60,000–100,000 kilograms or more in mass. Bipedal, as their size increased they evolved a four-legged graviportal gait adapted only to walking on land, like elephants; the early sauropodomorphs were most omnivores as their shared common ancestor with the other saurischian lineage was a carnivore. Therefore, their evolution to herbivory went hand in hand with their increasing size and neck length, they had large nostrils, retained a thumb with a big claw, which may have been used for defense — though their primary defensive adaptation was their extreme size. Sauropodomorphs can be distinguished as a group on the basis of some of the following synapomorphies: The presence of large nares; the distal part of the tibia is covered by an ascending process of the astragalus. Their hind limbs are short.
The presence of three or more sacral vertebrae. The teeth are thin and are spatula-like, with bladed and serrated crowns; the presence of a minimum of 10 cervical vertebrae that are elongated The presence of 25 presacral vertebrae The manus had a large digit I Among the first dinosaurs to evolve in the Late Triassic Period, about 230 million years ago, they became the dominant herbivores by halfway through the late Triassic. Their perceived decline in the early Cretaceous is most a bias in fossil sampling, as most fossils are known from Europe and North America. Sauropods were still the dominant herbivores in the Gondwanan landmasses, however; the spread of flowering plants and "advanced" ornithischians, another major group of herbivorous dinosaurs, are most not a major factor in sauropod decline in the northern continents. Like all non-avian dinosaurs, the sauropodomorphs became extinct 66 Mya, during the Cretaceous–Paleogene extinction event; the earliest and most basal sauropodomorphs known are Chromogisaurus novasi and Panphagia protos, both from the Ischigualasto Formation, dated to 231.4 million years ago.
Some studies have found Eoraptor lunensis, traditionally considered a theropod, to be an early member of the sauropodomorph lineage, which would make it the most basal sauropodomorph known. Sauropodomorpha is one of the two major clades within the order Saurischia; the sauropodomorphs' sister group, the Theropoda, includes bipedal carnivores like Velociraptor and Tyrannosaurus. However, sauropodomorphs share a number of characteristics with the Ornithischia, so a small minority of palaeontologists, like Bakker, have placed both sets of herbivores within a group called "Phytodinosauria" or "Ornithischiformes". In Linnaean taxonomy, Sauropodomorpha is left unranked, it was established by Friedrich von Huene in 1932, who broke it into two groups: the basal forms within Prosauropoda, their descendants, the giant Sauropoda. Phylogenetic analyses by Adam Yates and others placed Sauropoda within a paraphyletic "Prosauropoda". Recent cladistic analyses suggest that the clade Prosauropoda, named by Huene in 1920 and was defined by Sereno, in 1998, as all animals more related to Plateosaurus engelhardti than to Saltasaurus loricatus, is a junior synonym of Plateosauridae as both contain the same taxa.
Most modern classification schemes break the prosauropods into a half-dozen groups that evolved separately from one common lineage. While they have a number of shared characteristics, the evolutionary requirements for giraffe-like browsing high in the trees may have caused convergent evolution, where similar traits evolve separately because they faced the same evolutionary pressure, instead of trait
Alamosaurus is a genus of titanosaurian sauropod dinosaurs, containing a single known species, Alamosaurus sanjuanensis, from the late Cretaceous Period of what is now southern North America. Isolated vertebrae and limb bones indicate that it reached sizes comparable to Argentinosaurus and Puertasaurus, which would make it the largest dinosaur known from North America, its fossils have been recovered from a variety of rock formations spanning the Maastrichtian age of the late Cretaceous period. Specimens of a juvenile Alamosaurus sanjuanensis have been recovered from only a few meters below the Cretaceous-Paleogene boundary in Texas, making it among the last surviving non-avian dinosaur species. Alamosaurus was a gigantic quadrupedal herbivore with a long neck and tail and long limbs, its body was at least covered in bony armor. The total length of Alamosaurus is estimated to be 30 meters long. Though most of the complete remains come from juvenile or small adult specimens, three fragmentary specimens, SMP VP−1625, SMP VP−1850 and SMP VP−2104, suggest that adult Alamosaurus could have grown to enormous sizes comparable to the largest known dinosaurs like Argentinosaurus, estimated to weigh 73 metric tons.
Scott Hartman estimates Alamosaurus being shorter at 28–30 m and is equal in weight to other massive titanosaurs such as Argentinosaurus and Puertasaurus. However, he says that at the moment, scientists do not know whether the massive tibia belongs to an Alamosaurus or a new species of sauropod. Though no skull has been found, rod-shaped teeth have been found with Alamosaurus skeletons and belonged to this dinosaur; the vertebrae from the middle part of its tail had elongated centra. Alamosaurus had vertebral lateral fossae. Fossae that resemble shallow depressions are known from Saltasaurus, Malawisaurus and Gondwanatitan. Venenosaurus had depression-like fossae, but its "depressions" penetrated deeper into the vertebrae, were divided into two chambers, extend farther into the vertebral columns. Alamosaurus had more robust radii than Venenosaurus. Alamosaurus remains have been discovered throughout the southwestern United States; the holotype was discovered in June 1921 by Charles Whitney Gilmore, John Bernard Reeside and Charles Hazelius Sternberg at the Barrel Springs Arroyo in the Naashoibito Member of the Ojo Alamo Formation of New Mexico, deposited during the Maastrichtian stage of the Late Cretaceous Period.
Bones have been recovered from other Maastrichtian formations, like the North Horn Formation of Utah and the Black Peaks, El Picacho and Javelina Formations of Texas. Undescribed titanosaur fossils associated with Alamosaurus have been found in the Evanston Formation in Wyoming. Three articulated caudal vertebrae were collected above Hams Fork, are housed at the Museum of Paleontology, University of California, Berkeley; these specimens have not been described. Smithsonian paleontologist Gilmore described the holotype, USNM 10486, a left scapula, the paratype USNM 10487, a right ischium in 1922, naming the type species Alamosaurus sanjuanensis. Contrary to popular assertions, the dinosaur is not named after the Alamo in San Antonio, Texas, or the battle, fought there; the holotype, the specimen the name was based on, was discovered in New Mexico and, at the time of its naming, Alamosaurus had not yet been found in Texas. Instead, the name Alamosaurus comes from Ojo Alamo, the geologic formation in which it was found and which was, in turn, named after the nearby Ojo Alamo trading post.
The term alamo itself is a Spanish word meaning "poplar" and is used for the local subspecies of cottonwood tree. The term saurus is derived from saura, Greek for "lizard" and is the most common suffix used in dinosaur names. There is only one species in the genus, Alamosaurus sanjuanensis, named after San Juan County, New Mexico, where the first remains were found. In 1946, Gilmore posthumously described a more complete specimen, USNM 15660 found on June 15, 1937 on the North Horn Mountain of Utah by George B. Pearce, it consists of a complete tail, a right forelimb complete except for the fingers — which research showed do not ossify with the Titanosauridae — and both ischia. Since hundreds of other bits and pieces from Texas, New Mexico, Utah have been referred to Alamosaurus without much description. Despite being fragmentary, until the second half of the twentieth century they represented much of the globally known titanosaurid material; the most known specimen, TMM 43621-1, is a discovered juvenile skeleton from Texas, which allowed educated estimates of length and mass.
Some blocks catalogued under the same accession number as the complete and well-known Alamosaurus specimen USNM 15660, found in close proximity to it based on bone impressions, were first investigated by Michael Brett-Surman in 2009. In 2015, he reported that the blocks contained osteoderms, the first confirmation of their existence on Alamosaurus. No skull material is known, except for a few slender teeth. Gilmore in 1922 was uncertain about the precise affinities of Alamosaurus and did not determine it any further than a general Sauropoda. In 1927 Friedrich von Huene placed it in the Titanosauridae. Alamosaurus was in any case an advanced, or derived, member of the group Titanosauria, but its relationships within that gro
The Gobi Desert is a large desert or brushland region in Asia. It covers parts of Northern and Northeastern China, of southern Mongolia; the desert basins of the Gobi are bounded by the Altai Mountains and the grasslands and steppes of Mongolia on the north, by the Taklamakan Desert to the west, by the Hexi Corridor and Tibetan Plateau to the southwest, by the North China Plain to the southeast. The Gobi is notable in history as part of the great Mongol Empire, as the location of several important cities along the Silk Road; the Gobi is a rain shadow desert, formed by the Tibetan Plateau blocking precipitation from the Indian Ocean reaching the Gobi territory. The Gobi measures over 1,600 km from 800 km from north to south; the desert is widest in the west, along the line joining the Lop Nor. It occupies an arc of land 1,295,000 km2 in area as of 2007. Much of the Gobi has exposed bare rock. In its broadest definition, the Gobi includes the long stretch of desert extending from the foot of the Pamirs to the Greater Khingan Mountains, 116°-118° east, on the border of Manchuria.
A large area on the east side of the Greater Khingan range, between the upper waters of the Songhua and the upper waters of the Liao-ho, is reckoned to belong to the Gobi by conventional usage. Some geographers and ecologists prefer to regard the western area of the Gobi region: the basin of the Tarim in Xinjiang and the desert basin of Lop Nor and Hami, as forming a separate and independent desert, called the Taklamakan Desert. Archeologists and paleontologists have done excavations in the Nemegt Basin in the northwestern part of the Gobi Desert, noted for its fossil treasures, including early mammals, dinosaur eggs, prehistoric stone implements, some 100,000 years old; the Gobi is overall a cold desert, with frost and snow occurring on its dunes. Besides being quite far north, it is located on a plateau 910–1,520 metres above sea level, which contributes to its low temperatures. An average of 194 millimetres of rain falls annually in the Gobi. Additional moisture reaches parts of the Gobi in winter as snow is blown by the wind from the Siberian Steppes.
These winds may cause the Gobi to reach −40 °C in winter to 45 °C in summer. However, the climate of the Gobi is one of great extremes, combined with rapid changes of temperature of as much as 35 °C; these can occur not within 24 hours. In southern Mongolia, the temperature has been recorded as low as −32.8 °C. In contrast, in Alxa, Inner Mongolia, it rises as high as 37 °C in July. Average winter minimums are a frigid −21 °C, while summertime maximums are a warm 27 °C. Most of the precipitation falls during the summer. Although the southeast monsoons reach the southeast parts of the Gobi, the area throughout this region is characterized by extreme dryness during the winter, when the Siberian anticyclone is at its strongest; the southern and central parts of the Gobi Desert have variable plant growth due to this monsoon activity. The more northern areas of the Gobi are cold and dry, making it unable to support much plant growth. Hence, the icy snowstorms of spring and early summer plus early January.
The Gobi Desert is the source including the first dinosaur eggs. Despite the harsh conditions, these deserts and the surrounding regions sustain many animals, including black-tailed gazelles, marbled polecats, wild Bactrian camels, Mongolian wild ass and sandplovers, they are visited by snow leopards, brown bears, wolves. Lizards are well-adapted to the climate of the Gobi Desert, with 30 species distributed across its southern Mongolian border; the most common vegetation in the Gobi desert are shrubs adapted to drought. These shrubs included gray sparrow's saltwort, gray sagebrush, low grasses such as needle grass and bridlegrass. Due to livestock grazing, the amount of shrubs in the desert has decreased. Several large nature reserves have been established in the Gobi, including Gobi Gurvansaikhan National Park, Great Gobi A and Great Gobi B Strictly Protected Area; the area is vulnerable to trampling by livestock and off-road vehicles. In Mongolia, grasslands have been degraded by goats, which are raised by nomadic herders as source of cashmere wool.
Large copper deposits are being mined by Rio Tinto Group. The mine remains controversial. There was significant opposition in Mongolia's parliament to the terms under which the mine will proceed, some are calling for the terms to be renegotiated; the contention revolves around the question of whether negotiations were fair and whether Rio Tinto will pay adequate taxes on the revenues it derives from the mine (an agreement was reached whereby the operation will be exempt from windfall tax. The Gobi Desert is expanding at an alarming rate, in a process known as desertification; the expansion is rapid on the southern edge into China, which has seen 3,600 km2 (1,390
Mongolia is a landlocked country in East Asia. Its area is equivalent with the historical territory of Outer Mongolia, that term is sometimes used to refer to the current state, it is sandwiched between China to Russia to the north. Mongolia does not share a border with Kazakhstan. At 1,564,116 square kilometres, Mongolia is the 18th-largest and the most sparsely populated sovereign state in the world, with a population of around three million people, it is the world's second-largest landlocked country behind Kazakhstan and the largest landlocked country that does not border a closed sea. The country contains little arable land, as much of its area is covered by grassy steppe, with mountains to the north and west and the Gobi Desert to the south. Ulaanbaatar, the capital and largest city, is home to about 45% of the country's population. Ulaanbaatar shares the rank of the world's coldest capital city with Moscow and Nur-Sultan. 30% of the population is nomadic or semi-nomadic. The majority of its population are Buddhists.
The non-religious population is the second largest group. Islam is the dominant religion among ethnic Kazakhs; the majority of the state's citizens are of Mongol ethnicity, although Kazakhs and other minorities live in the country in the west. Mongolia joined the World Trade Organization in 1997 and seeks to expand its participation in regional economic and trade groups; the area of what is now Mongolia has been ruled by various nomadic empires, including the Xiongnu, the Xianbei, the Rouran, the Turkic Khaganate, others. In 1206, Genghis Khan founded the Mongol Empire, which became the largest contiguous land empire in history, his grandson Kublai Khan conquered China to establish the Yuan dynasty. After the collapse of the Yuan, the Mongols retreated to Mongolia and resumed their earlier pattern of factional conflict, except during the era of Dayan Khan and Tumen Zasagt Khan. In the 16th century, Tibetan Buddhism began to spread in Mongolia, being further led by the Manchu-founded Qing dynasty, which absorbed the country in the 17th century.
By the early 1900s one-third of the adult male population were Buddhist monks. After the collapse of the Qing dynasty in 1911, Mongolia declared independence, achieved actual independence from the Republic of China in 1921. Shortly thereafter, the country came under the control of the Soviet Union, which had aided its independence from China. In 1924, the Mongolian People's Republic was founded as a socialist state. After the anti-Communist revolutions of 1989, Mongolia conducted its own peaceful democratic revolution in early 1990; this led to a multi-party system, a new constitution of 1992, transition to a market economy. Homo erectus inhabited Mongolia from 850,000 years ago. Modern humans reached Mongolia 40,000 years ago during the Upper Paleolithic; the Khoit Tsenkher Cave in Khovd Province shows lively pink and red ochre paintings of mammoths, bactrian camels, ostriches, earning it the nickname "the Lascaux of Mongolia". The venus figurines of Mal'ta testify to the level of Upper Paleolithic art in northern Mongolia.
Neolithic agricultural settlements, such as those at Norovlin, Tamsagbulag and Rashaan Khad, predated the introduction of horse-riding nomadism, a pivotal event in the history of Mongolia which became the dominant culture. Horse-riding nomadism has been documented by archeological evidence in Mongolia during the Copper and Bronze Age Afanasevo culture; the wheeled vehicles found in the burials of the Afanasevans have been dated to before 2200 BC. Pastoral nomadism and metalworking became more developed with the Okunev culture, Andronovo culture and Karasuk culture, culminating with the Iron Age Xiongnu Empire in 209 BC. Monuments of the pre-Xiongnu Bronze Age include deer stones, keregsur kurgans, square slab tombs, rock paintings. Although cultivation of crops has continued since the Neolithic, agriculture has always remained small in scale compared to pastoral nomadism. Agriculture arose independently in the region; the population during the Copper Age has been described as mongoloid in the east of what is now Mongolia, as europoid in the west.
Tocharians and Scythians inhabited western Mongolia during the Bronze Age. The mummy of a Scythian warrior, believed to be about 2,500 years old, was a 30- to 40-year-old man with blond hair; as equine nomadism was introduced into Mongolia, the political center of the Eurasian Steppe shifted to Mongolia, where it remained until the 18th century CE. The intrusions of northern pastoralists into China during the Shang dynasty and Zhou dynasty presaged the age of nomadic empires; the concept of Mongolia as an independent power north of China is expressed in a letter sent by Emperor Wen of Han to Laoshang Chanyu in 162 BC: Since prehistoric times, Mongolia has been inhabited by nomads who, from time to time, formed great confederations that rose to power and prominence. Common institutions were the office of the Khan, the Kurultai and right wings, imperial army and the decimal military system; the first of these empires, the Xiongnu of undetermined
Bonitasaura is a titanosaurian dinosaur hailing from uppermost layers of the Late Cretaceous Bajo de la Carpa Formation, Neuquén Group of the eastern Neuquén Basin, located in Río Negro Province, Northwestern Patagonia, Argentina. The remains, consisting of a partial sub-adult skeleton jumbled in a small area of fluvial sandstone, including lower jaw with teeth, partial vertebrae series and limb bones, were described by Sebastian Apesteguía in 2004; the genus name Bonitasaura refers to the fossil quarry’s name, "La Bonita", while the name of the type species, B. salgadoi, pays homage to Leonardo Salgado, a renowned Argentine palaeontologist. Bonitasaura measured 10 metres in length, had a skull similar to another group of sauropods, the diplodocids; the lower jaw had a distinctive, sharp ridge behind a reduced set of teeth. This ridge supported in life a sharp, beak-like keratin sheath that paired with a similar structure in the upper jaw; the keratin sheath worked much like a guillotine to crop vegetation raked into the mouth by the peg-like front teeth.
This animal had a rather short neck and robust projections of the back vertebrae for muscle attachment, indicating that the neck was used in vigorous exertions during feeding. Bonitasaura shows that some lines of titanosaurian evolution converged with diplodocids, namely low long skulls without the characteristic nasal arches of other macronarians and lower jaws that were squared off and contained comb-like teeth, reversed limb proportions and rudimentary whiplash tails, it threw a wrench into the suggestion by some authors that the titanosaur Antarctosaurus is a chimera made up of a titanosaurian skull and body and a diplodocoid jaw. Bonitasaura was classified as a member of Nemegtosauridae in the original description, but subsequent cladistic analyses and description found it to be nested among the titanosaur clade that includes Lognkosauria and Rinconsauria. Apesteguía, S. 2004. Bonitasaura salgadoi gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia. Naturwissenschaften 91.
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