The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago, to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era; as with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when 60% of marine species were wiped out. A significant evolutionary milestone during the Silurian was the diversification of jawed fish and bony fish. Multi-cellular life began to appear on land in the form of small, bryophyte-like and vascular plants that grew beside lakes and coastlines, terrestrial arthropods are first found on land during the Silurian. However, terrestrial life would not diversify and affect the landscape until the Devonian; the Silurian system was first identified by British geologist Roderick Murchison, examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s.
He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, from the Latin name for Wales. This naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures. In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales, the germ of the modern geological time scale; as it was first identified, the "Silurian" series when traced farther afield came to overlap Sedgwick's "Cambrian" sequence, provoking furious disagreements that ended the friendship. Charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was "Gotlandian" after the strata of the Baltic island of Gotland; the French geologist Joachim Barrande, building on Murchison's work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge.
He divided the Silurian rocks of Bohemia into eight stages. His interpretation was questioned in 1854 by Edward Forbes, the stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils; the Llandovery Epoch lasted from 443.8 ± 1.5 to 433.4 ± 2.8 mya, is subdivided into three stages: the Rhuddanian, lasting until 440.8 million years ago, the Aeronian, lasting to 438.5 million years ago, the Telychian. The epoch is named for the town of Llandovery in Wales; the Wenlock, which lasted from 433.4 ± 1.5 to 427.4 ± 2.8 mya, is subdivided into the Sheinwoodian and Homerian ages. It is named after Wenlock Edge in England. During the Wenlock, the oldest-known tracheophytes of the genus Cooksonia, appear; the complexity of later Gondwana plants like Baragwanathia, which resembled a modern clubmoss, indicates a much longer history for vascular plants, extending into the early Silurian or Ordovician.
The first terrestrial animals appear in the Wenlock, represented by air-breathing millipedes from Scotland. The Ludlow, lasting from 427.4 ± 1.5 to 423 ± 2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, the Ludfordian stage. It is named for the town of Ludlow in England; the Přídolí, lasting from 423 ± 1.5 to 419.2 ± 2.8 mya, is the final and shortest epoch of the Silurian. It is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a cadastral field area. In North America a different suite of regional stages is sometimes used: Cayugan Lockportian Tonawandan Ontarian Alexandrian In Estonia the following suite of regional stages is used: Ohessaare stage Kaugatuma stage Kuressaare stage Paadla stage Rootsiküla stage Jaagarahu stage Jaani stage Adavere stage Raikküla stage Juuru stage With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe.
The high sea levels of the Silurian and the flat land resulted in a number of island chains, thus a rich diversity of environmental settings. During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late-Ordovician glaciation; the southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity; the continents of Avalonia and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. When the proto-Europe coll
The Permian is a geologic period and system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago, to the beginning of the Triassic period 251.902 Mya. It is the last period of the Paleozoic era; the concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm. The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals, turtles and archosaurs; the world at the time was dominated by two continents known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors; the Permian ended with the Permian–Triassic extinction event, the largest mass extinction in Earth's history, in which nearly 96% of marine species and 70% of terrestrial species died out.
It would take well into the Triassic for life to recover from this catastrophe. Recovery from the Permian–Triassic extinction event was protracted; the term "Permian" was introduced into geology in 1841 by Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Édouard de Verneuil; the region now lies in the Perm Krai of Russia. Official ICS 2017 subdivisions of the Permian System from most recent to most ancient rock layers are: Lopingian epoch Changhsingian Wuchiapingian Others: Waiitian Makabewan Ochoan Guadalupian epoch Capitanian stage Wordian stage Roadian stage Others: Kazanian or Maokovian Braxtonian stage Cisuralian epoch Kungurian stage Artinskian stage Sakmarian stage Asselian stage Others: Telfordian Mangapirian Sea levels in the Permian remained low, near-shore environments were reduced as all major landmasses collected into a single continent—Pangaea; this could have in part caused the widespread extinctions of marine species at the end of the period by reducing shallow coastal areas preferred by many marine organisms.
During the Permian, all the Earth's major landmasses were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean, the Paleo-Tethys Ocean, a large ocean that existed between Asia and Gondwana; the Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys Ocean to shrink. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic era. Large continental landmass interiors experience climates with extreme variations of heat and cold and monsoon conditions with seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea; such dry conditions favored gymnosperms, plants with seeds enclosed in a protective cover, over plants such as ferns that disperse spores in a wetter environment. The first modern trees appeared in the Permian. Three general areas are noted for their extensive Permian deposits—the Ural Mountains and the southwest of North America, including the Texas red beds.
The Permian Basin in the U. S. states of Texas and New Mexico is so named because it has one of the thickest deposits of Permian rocks in the world. The climate in the Permian was quite varied. At the start of the Permian, the Earth was still in an ice age. Glaciers receded around the mid-Permian period as the climate warmed, drying the continent's interiors. In the late Permian period, the drying continued although the temperature cycled between warm and cool cycles. Permian marine deposits are rich in fossil mollusks and brachiopods. Fossilized shells of two kinds of invertebrates are used to identify Permian strata and correlate them between sites: fusulinids, a kind of shelled amoeba-like protist, one of the foraminiferans, ammonoids, shelled cephalopods that are distant relatives of the modern nautilus. By the close of the Permian, trilobites and a host of other marine groups became extinct. Terrestrial life in the Permian included diverse plants, fungi and various types of tetrapods; the period saw a massive desert covering the interior of Pangaea.
The warm zone spread in the northern hemisphere. The rocks formed at that time were stained red by iron oxides, the result of intense heating by the sun of a surface devoid of vegetation cover. A number of older types of plants and animals became marginal elements; the Permian began with the Carboniferous flora still flourishing. About the middle of the Permian a major transition in vegetation began; the swamp-loving
Heteromyidae is a family of rodents consisting of kangaroo rats, kangaroo mice, pocket mice and spiny pocket mice. Most heteromyids live in complex burrows within the deserts and grasslands of western North America, though species within the genus Heteromys are found in forests and their range extends down as far as northern South America, they feed on seeds and other plant parts, which they carry in their fur-lined cheek pouches to their burrows. Although they are different in physical appearance, the closest relatives of the heteromyids are pocket gophers in the family Geomyidae. There are about fifty-nine members of the family Heteromyidae divided among six genera, they are all small rodents, the largest being the giant kangaroo rat with a body length of 15 cm and a tail a little longer than this. In many species the tail is tufted and is used for balance. Other adaptations include fused vertebrae in the neck, short fore limbs and much enlarged bullae; the skulls vary across the group but they are all thin and papery and do not have the robust cranial crests and ridges found on the skulls of members of the family Geomyidae.
The skull has other peculiarities. There is an extra hole that penetrates the rostrum, distinctive occluded teeth and the masseter muscle, which moves the lower jaw, is set far forward on the snout, an arrangement found in squirrels, pocket gophers, heteromyids and a few other groups; the dental formula is 188.8.131.52.0.1.3 × 2 = 20 teeth in total. In the kangaroo rats, the teeth continue to grow all the time; the molars have two-lobed cusps. The upper incisors are grooved and the enamel on the molars is worn away by chewing leaving the dentine exposed. In the kangaroo rats they are unrooted but in the pocket mice they have roots. Fur-lined cheek pouches are a feature across the family Heteromyidae, they extend backwards along the sides of the neck. The fur on the animal's body is in general short and fine and matches in colour the soil of the region in which the animal lives, being some shade of buff, pale brown, reddish-brown or grey; the spiny pocket mice spiky bristles on the back near the tail.
Heteromyids are endemic to the western United States, Central America and northwestern South America. They are creatures of open country specialising in prairies, arid lands and desert fringes, but the spiny pocket mice are found in both wet and dry tropical forests in Central and northwestern South America. During the Oligocene, the extent of arid lands across the United States was greater than it is today and these animals occurred more widely. Fossils of kangaroo rats are known from the Pliocene; the kangaroo rats, kangaroo mice and pocket mice are adapted for life in deserts and other arid environments where they feed on dry seeds. Kangaroo rats have no need to drink because they are able to extract sufficient water from metabolising their food, obtaining half a gram of water from each gram of seeds eaten, they carry most of the seeds they find back to their burrows in exterior cheek folds lined with fur rather than in cheek pouches inside the mouth as do hamsters. This is because carrying the food in the mouth would involve wetting it and moisture needs to be conserved as much as possible in dry environments.
Most species store the seeds they gather in special chambers in the burrow where they absorb moisture from the humid air. Others, such as Merriam's kangaroo rat, bury them in shallow caches in the open air, it has been found that there is little hoarding done in the winter but that food is most stored in the autumn and spring. Heteromyds use sight and olfactory clues to locate possible food and use their fore-feet to manipulate objects. Kangaroo mice make greater use of clumped food where wind or water has concentrated seeds in shallow depressions or around rocks while pocket mice hunt around under vegetation or debris for individual food items, it has been found that pocket mice forage more efficiently than kangaroo rats and this is thought to be due to the fact that they handle their finds more and are better able to distinguish between food and non-food items. These animals excavate long burrow systems with passages and multiple entrances, they are nocturnal and moving about at night and resting deep in their burrows during the day.
Here it is cooler and more humid which conserves moisture and the animals may temporarily block the entrances to augment this. They are able to concentrate their urine to a viscous consistency. Under extreme conditions, some are able to aestivate in chambers under ground. Kangaroo rats have large hind feet with no first digits. With these they bound around not using their fore feet at all for locomotion. Pocket mice are smaller and can move with leaps but they run around on four limbs. Members of the genus Heteromys, the spiny pocket mice, move around on all fours and do not leap at all. Kangaroo rats and pocket mice form a part of the diet of many predatory creatures, they are eaten by foxes, coyotes and birds. They can detect the approaching swoop of an owl or the movements of a snake. Many can leap to avoid the predators; the largest kangaroo rats can leap 2.75 metres in a single bound. In the Sonoran Desert there are many related species of heteromyid mice and rats; each has its own niche in the environment which means that they do not unnecessarily compete with each other for the limited available resources.
Bailey’s pocket mouse climbs into plants and bushes in order to find seeds and berries
Elliott Coues was an American army surgeon, historian and author. Elliott Ladd Coues was born in Portsmouth, New Hampshire to Samuel Elliott Coues and Charlotte Haven Ladd Coues, he graduated at Columbian University, Washington, D. C. in 1861, at the Medical school of that institution in 1863. He served as a medical cadet in Washington in 1862–1863, in 1864 was appointed assistant-surgeon in the regular army, assigned to Fort Whipple, Arizona. While there was not yet any legal provision for divorce under its laws, the 1st Arizona State Legislature granted Coues an annullment of his marriage to Sarah A. Richardson. In 1872 he published his Key to North American Birds, which and rewritten in 1884 and 1901, did much to promote the systematic study of ornithology in America, he was a founding member of the American Ornithologists' Union in 1883. His work was instrumental in establishing the accepted standards of trinomial nomenclature – the taxonomic classification of subspecies – in ornithology, the whole of zoology.
During 1873–1876 Coues was attached as surgeon and naturalist to the United States Northern Boundary Commission, from 1876 to 1880 he was secretary and naturalist to the United States Geological and Geographical Survey of the Territories, the publications of which he edited. He was lecturer on anatomy in the medical school of the Columbian University from 1877 to 1882, professor of anatomy there from 1882 to 1887, he was a careful bibliographer and in his work on the Birds of the Colorado Valley he included a special section on swallows and attempted to resolve whether they migrated in winter or hibernated under lakes as was believed at the time: I have never seen anything of the sort, nor have I known one who had seen it. But I have no means of refuting the evidence, cannot refuse to recognize its validity. Nor have I aught to urge against it, beyond the degree of incredibility that attaches to exceptional and improbable allegations in general, in particular the difficulty of understanding the alleged abruptness of the transition from activity to torpor.
I cannot consider the evidence as inadmissible, must admit that the alleged facts are as well attested, according to ordinary rules of evidence, as any in ornithology. It is useless as well as unscientific to pooh-pooh the notion; the asserted facts are nearly identical with the known cases of many batrachians. They are strikingly like the known cases of many bats, they accord in general with the recognized conditions of hibernation in many mammals. He resigned from the army in 1881 to devote himself to scientific research, he was a founder of the American Ornithologists' Union, edited its organ, The Auk, several other ornithological periodicals. He died in Maryland. Grace's warbler was discovered by Elliott Coues in the Rocky Mountains in 1864, he requested that the new species be named after his 18-year-old sister, Grace Darling Coues, his request was honored when Spencer Fullerton Baird described the species scientifically in 1865. In addition to ornithology he did valuable work in mammalogy.
Odocoileus virginianus couesi, the Coues white-tailed deer is named after him. Coues began speculations in Theosophy, he was a friend of Alfred Russel Wallace and they had attended séances with the medium Pierre L. O. A. Keeler, he felt the inadequacy of formal orthodox science in dealing with the deeper problems of human life and destiny. Convinced by the principles of evolution, he believed that these principles may be capable of being applied in psychical research and he proposed to use it to explain obscure phenomena such as hypnotism and telepathy, he claimed to have witnessed levitation of objects and developed a theory to explain the phenomenon, publishing an article about his telekinetic theory of levitation in the first issue of The Metaphysical Magazine. Coues joined the Theosophical Society in July, 1884, he visited Helena Blavatsky in Europe. He founded the Gnostic Theosophical Society of Washington, in 1890 became the president of the Theosophical Society, he became critical of Blavatsky and lost interest in the Theosophical movement.
Coues wrote an attack on Blavatsky entitled "Blavatsky Unveiled!" in The Sun newspaper on July 20, 1890. The article prompted Blavatsky to file a legal suit against Coues and the newspaper but it was terminated as she passed away in 1891, he fell out with Theosophical leaders such as William Quan Judge and was expelled from the Theosophical Society in June, 1899 for "untheosophical conduct". Coues retained interest in oriental religious thought and studied Islam. Among the most important of his publications are: A Field Ornithology. Rural Bird Life of England, with Charles Dixon. Coues contributed numerous articles to the Century Dictionary, wrote for various encyclopaedias, edited: Journals of Lewis and Clark. Pike.
The Sonoran Desert is a North American desert which covers large parts of the Southwestern United States in Arizona and California and of Northwestern Mexico in Sonora, Baja California, Baja California Sur. It is the hottest desert in Mexico, it has an area of 260,000 square kilometers. The western portion of the United States–Mexico border passes through the Sonoran Desert. In phytogeography, the Sonoran Desert is within the Sonoran Floristic Province of the Madrean Region in southwestern North America, part of the Holarctic Kingdom of the northern Western Hemisphere; the desert contains a variety of unique and endemic plants and animals, such as the saguaro and organ pipe cactus. The Sonoran desert wraps around the northern end of the Gulf of California, from Baja California Sur, north through much of Baja California, excluding the central northwest mountains and Pacific west coast, through southeastern California and southwestern and southern Arizona to western and central parts of Sonora.
It is bounded on the west by the Peninsular Ranges, which separate it from the California chaparral and woodlands and Baja California Desert ecoregions of the Pacific slope. To the north in California and northwest Arizona, the Sonoran Desert transitions to the colder-winter, higher-elevation Mojave, Great Basin, Colorado Plateau deserts. To the east and southeast, the deserts transition to the coniferous Arizona Mountains forests and Sierra Madre and Sierra Madre Occidental pine–oak forests at higher elevations. To the south the Sonoran–Sinaloan transition subtropical dry forest is the transition zone from the Sonoran Desert to the tropical dry forests of the Mexican state of Sinaloa; the desert's sub-regions include the Colorado Desert of southeastern California. In the 1957 publication Vegetation of the Sonoran Desert, Forrest Shreve divided the Sonoran Desert into seven regions according to characteristic vegetation: Lower Colorado Valley, Arizona Upland, Plains of Sonora, Foothills of Sonora, Central Gulf Coast, Vizcaíno Region, Magdalena Region.
Many ecologists now consider Shreve's Vizcaíno and Magdalena regions, which lie on the western side of the Baja California Peninsula, to be a separate ecoregion, the Baja California Desert. Within the southern Sonoran Desert in Mexico is found the Gran Desierto de Altar, with the Reserva de la Biosfera el Pinacate y Gran Desierto de Altar, extending 2,000 square kilometers of desert and mountainous regions; the Pinacate National Park includes the only active erg dune region in North America. The nearest city to the Reserva de la Biosfera el Pinacate y Gran Desierto de Altar is Puerto Peñasco in the state of Sonora, Mexico. Sub-regionsSonoran Desert sub-regions include: Colorado Desert Gran Desierto de Altar Lechuguilla Desert Tonopah Desert Yuha Desert Yuma Desert The Sonoran Desert includes 60 mammal species, 350 bird species, 20 amphibian species, over 100 reptile species, 30 native fish species, over 1000 native bee species, more than 2,000 native plant species; the Sonoran Desert area southeast of Tucson and near the Mexican border is vital habitat for the only population of jaguars living within the United States.
The Colorado River Delta was once an ecological hotspot within the Sonoran desert, fueled by the flow of fresh water through the Colorado river in this otherwise dry area, but the delta has been reduced in extent due to the damming and use of the river upstream. Many plants not only thrive in the harsh conditions of the Sonoran Desert. Many have evolved to have specialized adaptations to the desert climate; the Sonoran Desert's biseasonal rainfall pattern results in more plant species than any other desert in the world. The Sonoran Desert includes plant genera and species from the agave family, palm family, cactus family, legume family, numerous others; the Sonoran is the only place in the world. Cholla, hedgehog, prickly pear, nightblooming cereus, organ pipe are other taxa of cacti found here. Cactus provides food and homes to many desert mammals and birds, with showy flowers in reds, pinks and whites, blooming most from late March through June, depending on the species and seasonal temperatures.
Creosote bush and bur sage dominate valley floors. Indigo bush and Mormon tea are other shrubs. Wildflowers of the Sonoran Desert include desert sand verbena, desert sunflower, evening primroses. Ascending from the valley up bajadas, various subtrees such as velvet mesquite, palo verde, desert ironwood, desert willow, crucifixion thorn are common, as well as multi-stemmed ocotillo. Shrubs found at higher elevations include whitethorn acacia, fairy duster, jojoba. In the desert subdivisions found on Baja California, cardon cactus, elephant tree, boojum tree occur; the California fan palm is found in the Colorado Desert section of the Sonoran Desert, the only native palm in California, among many other introduced Arecac
The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period 485.4 million years ago to the start of the Silurian Period 443.8 Mya. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, placed them in a system of their own; the Ordovician received international approval in 1960, when it was adopted as an official period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it did in the earlier Cambrian period, although the end of the period was marked by the Ordovician–Silurian extinction events.
Invertebrates, namely molluscs and arthropods, dominated the oceans. The Great Ordovician Biodiversification Event increased the diversity of life. Fish, the world's first true vertebrates, continued to evolve, those with jaws may have first appeared late in the period. Life had yet to diversify on land. About 100 times as many meteorites struck the Earth per year during the Ordovician compared with today; the Ordovician Period began with a major extinction called the Cambrian–Ordovician extinction event, about 485.4 Mya. It lasted for about 42 million years and ended with the Ordovician–Silurian extinction events, about 443.8 Mya which wiped out 60% of marine genera. The dates given are recent radiometric dates and vary from those found in other sources; this second period of the Paleozoic era created abundant fossils that became major petroleum and gas reservoirs. The boundary chosen for the beginning of both the Ordovician Period and the Tremadocian stage is significant, it correlates well with the occurrence of widespread graptolite and trilobite species.
The base of the Tremadocian allows scientists to relate these species not only to each other, but to species that occur with them in other areas. This makes it easier to place many more species in time relative to the beginning of the Ordovician Period. A number of regional terms have been used to subdivide the Ordovician Period. In 2008, the ICS erected a formal international system of subdivisions. There exist Baltoscandic, Siberian, North American, Chinese Mediterranean and North-Gondwanan regional stratigraphic schemes; the Ordovician Period in Britain was traditionally broken into Early and Late epochs. The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column; the faunal stages from youngest to oldest are: Late Ordovician Hirnantian/Gamach Rawtheyan/Richmond Cautleyan/Richmond Pusgillian/Maysville/Richmond Middle Ordovician Trenton Onnian/Maysville/Eden Actonian/Eden Marshbrookian/Sherman Longvillian/Sherman Soudleyan/Kirkfield Harnagian/Rockland Costonian/Black River Chazy Llandeilo Whiterock Llanvirn Early Ordovician Cassinian Arenig/Jefferson/Castleman Tremadoc/Deming/Gaconadian The Tremadoc corresponds to the Tremadocian.
The Floian corresponds to the lower Arenig. The Llanvirn occupies the rest of the Darriwilian, terminates with it at the base of the Late Ordovician; the Sandbian represents the first half of the Caradoc. During the Ordovician, the southern continents were collected into Gondwana. Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole. Early in the Ordovician, the continents of Laurentia and Baltica were still independent continents, but Baltica began to move towards Laurentia in the period, causing the Iapetus Ocean between them to shrink; the small continent Avalonia separated from Gondwana and began to move north towards Baltica and Laurentia, opening the Rheic Ocean between Gondwana and Avalonia. The Taconic orogeny, a major mountain-building episode, was well under way in Cambrian times. In the early and middle Ordovician, temperatures were mild, but at the beginning of the Late Ordovician, from 460 to 450 Ma, volcanoes along the margin of the Iapetus Ocean spewed massive amounts of carbon dioxide, a greenhouse gas, into the atmosphere, turning the planet into a hothouse.
Sea levels were high, but as Gondwana moved south, ice accumulated into glaciers and sea levels dropped. At first, low-lying sea beds increased diversity, but glaciation led to mass extinctions as the seas drained and continental shelves became dry land. During the Ordovician, in fact during the Tremadocian, marine transgressions worldwide were the greatest for which evidence is preserved; these volcanic island arcs collided with proto North America to form the Appalachian mountains. By the end of the Late Ordovician the volcanic emissions had stopped. Gondwana had by that time neared the South Pole and was glaciated
The Muddle-Headed Wombat
The Muddle-Headed Wombat is a fictional wombat featured in the radio serials and in the children's books of the same name written by Australian author Ruth Park. In 1941 the Australian Broadcasting Commission decided to nationalise its Children's programs, broadcast from Sydney with Ida Elizabeth Osbourne as its first producer. In 1942 she commissioned Ruth Park to write The Wide -- Awake Bunyip; the first episode was aired with "Joe" in the title role. When he died, in 1951, Ruth changed the title to The Muddle–Headed Wombat, with Leonard Teale the first to play the part; when Leonard left, John Ewart "Jimmy" made it his for the next 18 years. The part of his friend "Mouse" in both incarnations was played by the current female co-presenter; when John Appleton was made Supervisor of Children's Programs and keen to be involved, the part of "Tabby Cat" was created for him. The narrator throughout was "Mac"; the popularity of the series led Ruth Park to write her Muddle–Headed Wombat books. The Muddle-Headed Wombat books follow the Muddle-Headed Wombat and his friends, a good-natured, practical female mouse and a vain, neurotic male tabby cat.
The characters call each other Wombat and Tabby. Wombat's speech is peppered with malapropisms and spoonerisms, e.g. treely ruly for and lawn the mow for mow the lawn and Cindergorilla for Cinderella. He has a bicycle with red wheels, of which he is intensely proud and which he anthropomorphises, e.g. complaining that it bit him when he accidentally injured himself trying to repair it. The Muddle Headed Wombat series of books was published from 1962 to 1971 by Educational Press Pty Ltd, who commissioned Ruth Park to write books based on the radio show. Noela Young illustrated these books. In 1971 the rights were transferred to Angus and Robertson Pty Ltd, who commissioned the books and reprinted those published by Educational Press; the Muddle-Headed Wombat 1962 The Muddle-Headed Wombat on Holiday 1964 The Muddle-Headed Wombat in the Treetops 1965 The Muddle-Headed Wombat at School 1966 The Muddle-Headed Wombat in the Snow 1966 The Muddle-Headed Wombat on a Rainy Day 1969 The Muddle Headed Wombat in the Springtime 1970 The Muddle-Headed Wombat on the River 1970 The Muddle-Headed Wombat and the Bush Band 1973 The Muddle-Headed Wombat and the Invention 1975 The Muddle-Headed Wombat on Clean-Up Day 1976 The Adventures of the Muddle-Headed Wombat 1979 The Muddle-Headed Wombat 1979, contains:The Muddle-Headed Wombat The Muddle-Headed Wombat on Holiday The Muddle-Headed Wombat in the Treetops The Muddle-Headed Wombat at SchoolMore Adventures of the Muddle-Headed Wombat 1980 The Muddle-Headed Wombat is Very Bad 1981 The Muddle-Headed Wombat Stays at Home 1982 In Ukraine in 1990 was released short animated film "The Muddle-Headed Wombat" directed by Serguei Kouchnerov on Ukranimafilm studio