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 Cameroon scaly-tail referred to as the Cameroon anomalure, flightless anomalure, or flightless scaly-tail, is a rodent species endemic to West Central Africa. The scientific literature has never reported observations of live individuals; the taxonomic classification of the species has been subject to recent revision. Previous common names for this species included flightless scaly-tail ‘squirrel’, but this is a misnomer as anomalures are distantly related to the true squirrels of the rodent family Sciuridae and only superficially resemble them. Z. insignis is the only extant species in the genus Zenkerella and family Zenkerellidae and is the only surviving species of a lineage that diverged from the other extant anomalures ~49 million years ago. Among mammals few species are the sole survivors of such ancient lineages, some other examples being the pen-tailed treeshrew and the monito del monte. Extinct fossil taxa which are putative close relatives of Z. insignis include: Zenkerella wintoni, Prozenkerella saharaensis, Oromys zenkerellinopsis.
In 2016, it was reported that three whole-body specimens of Z. insignis were recovered on Bioko Island, Equatorial Guinea. At that time, it had been over 20 years since the scientific literature recorded new individuals; these specimens were used to sequence portions of the Z. insignis genome. Phylogenetic analysis using combined DNA and anatomical data place Zenkerella as the sister taxon of an Idiurus-Anomalurus clade; this is contrary to a previous hypothesis that grouped Zenkerella with Idiurus within the family Anomaluridae. The Z. insignis position in the rodent evolutionary tree supports a single origin of the anomalure gliding adaptation with no evolutionary reversals. The same analysis estimated an early Oligocene origin of anomalure gliding and an early Eocene divergence of the Z. insignis lineage. These results were used to justify a taxonomic revision that erected the new rodent family Zenkerellidae in which Z. insignis is the only living species. The anomalures, including Z. insignis, are unique among rodents in having a set of scales on the ventral surface of the base of the tail.
These scales provide traction when climbing trees. Z. insignis is the only anomalure. Anomalures that possess patagia are able to glide between trees. Thus, Z. insignis is unable to glide. The divergence of the Z. insignis lineage from other extant anomalures occurred before the evolution of anomalure gliding. Gliding is a rare adaptation that has independently evolved in three lineages of extant placental mammals. Z. insignis has bushy black tail hair. Tufts of short and spikey hairs are located on the lateral ankles; the hands and feet have five digits respectively. Pedal digit. Z. Insignis molars are distinct from other extant anomalures in having a continuous enamel crest that, in occlusal view, forms a full perimeter around the tooth and a single transverse crest divides the occlusal surface into two basins; the fossilized molars of Z. wintoni and P. saharaensis have these features and the lineage’s tooth morphology is unchanged since the early Oligocene. In mammals, dental morphology is an excellent indicator of the animal’s diet.
Sole survivorship of an ancient lineage combined with the retention of morphology are characteristics which identify Z. insignis as a ‘living fossil’. However, some biologists have questioned the usefulness of this popular term. There are no entries in the scientific literature that document direct observations of living Z. insignis individuals. Although the species was first described in 1898, trapping efforts have resulted in only 14 specimens deposited in world natural history museums. From these specimens, the geographic distribution of Z. insignis is recorded from south Cameroon, Equatorial Guinea, southwestern Central African Republic, Republic of Congo. The species is not recorded from Gabon but occurs there. Based on collection localities, Z. insignis inhabits semi-deciduous forests. Without direct scientific observation and diet are inferred from what is known of other anomalures and anecdotal information gathered by interviewing local people and subsistence trappers; the species is largely arboreal but occasional captures in ground snares indicates it sometimes comes to the ground.
Other anomalures are or nocturnal and sleep in tree-hollows during the day. The species is herbivorous; the IUCN assessed the species as Data Deficient, but in 2008 this was changed to the current listing of Least Concern as the species appears to have a wide distribution with extensive suitable habitat, occurs in several protected areas. However, some conservation biologists state that “This rating belies the fact that threats such as habitat loss and degradation are intense and widespread in central Africa” and “Zenkerella may be under greater threat”
Flight is the process by which an object moves through an atmosphere without contact with the surface. This can be achieved by generating aerodynamic lift associated with propulsive thrust, aerostatically using buoyancy, or by ballistic movement. Many things can fly, from natural aviators such as birds and insects, to human inventions like aircraft, including airplanes, helicopters and rockets which may carry spacecraft; the engineering aspects of flight are the purview of aerospace engineering, subdivided into aeronautics, the study of vehicles that travel through the air, astronautics, the study of vehicles that travel through space, in ballistics, the study of the flight of projectiles. Humans have managed to construct lighter than air vehicles that raise off the ground and fly, due to their buoyancy in air. An aerostat is a system that remains aloft through the use of buoyancy to give an aircraft the same overall density as air. Aerostats include free balloons and moored balloons. An aerostat's main structural component is its envelope, a lightweight skin that encloses a volume of lifting gas to provide buoyancy, to which other components are attached.
Aerostats are so named because they use "aerostatic" lift, a buoyant force that does not require lateral movement through the surrounding air mass to effect a lifting force. By contrast, aerodynes use aerodynamic lift, which requires the lateral movement of at least some part of the aircraft through the surrounding air mass; some things that fly do not generate propulsive thrust through the air, for example, the flying squirrel. This is termed gliding; some other things can exploit rising air to climb such as man-made sailplane gliders. This is termed soaring; however most other birds and all powered aircraft need a source of propulsion to climb. This is termed powered flight; the only groups of living things that use powered flight are birds and bats, while many groups have evolved gliding. The extinct Pterosaurs, an order of reptiles contemporaneous with the dinosaurs, were very successful flying animals; each of these groups' wings evolved independently. The wings of the flying vertebrate groups are all based on the forelimbs, but differ in structure.
Bats are the only mammals capable of sustaining level flight. However, there are several gliding mammals which are able to glide from tree to tree using fleshy membranes between their limbs. Flying frogs use enlarged webbed feet for a similar purpose, there are flying lizards which fold out their mobile ribs into a pair of flat gliding surfaces. "Flying" snakes use mobile ribs to flatten their body into an aerodynamic shape, with a back and forth motion much the same as they use on the ground. Flying fish can glide using enlarged wing-like fins, have been observed soaring for hundreds of meters, it is thought that this ability was chosen by natural selection because it was an effective means of escape from underwater predators. The longest recorded flight of a flying fish was 45 seconds. Most birds fly, with some exceptions; the largest birds, the ostrich and the emu, are earthbound, as were the now-extinct dodos and the Phorusrhacids, which were the dominant predators of South America in the Cenozoic era.
The non-flying penguins have wings adapted for use under water and use the same wing movements for swimming that most other birds use for flight. Most small flightless birds are native to small islands, lead a lifestyle where flight would offer little advantage. Among living animals that fly, the wandering albatross has up to 3.5 meters. Most species of insects can fly as adults. Insect flight makes use of either of two basic aerodynamic models: creating a leading edge vortex, found in most insects, using clap and fling, found in small insects such as thrips. Mechanical flight is the use of a machine to fly; these machines include aircraft such as airplanes, helicopters, airships, ornithopters as well as spacecraft. Gliders are capable of unpowered flight. Another form of mechanical flight is para-sailing. In an airplane, lift is created by the wings. There are different types of wings: tempered, semi-tempered, sweptback and elliptical. An aircraft wing is sometimes called an airfoil, a device that creates lift when air flows across it.
Supersonic flight is flight faster than the speed of sound. Supersonic flight is associated with the formation of shock waves that form a sonic boom that can be heard from the ground, is startling; this shockwave takes quite a lot of energy to create and this makes supersonic flight less efficient than subsonic flight at about 85% of the speed of sound. Hypersonic flight is high speed flight where the heat generated by the compression of the air due to the motion through the air causes chemical changes to the air. Hypersonic flight is achieved by reentering spacecraft such as Soyuz; some things generate little or no lift and move only or under the action of momentum, air drag and in some cases thrust. This is termed ballistic flight. Examples include balls, bullets, fireworks etc. An extreme form of ballistic flight, spaceflig
Anomaluromorpha is the name given to a clade that unites the anomalures with the springhares. It has alternately been designated as either a infraorder. Most Carleton & Musser 2005 recognized it as one of five suborders of rodents; the suborder Anomaluromorpha was erected to unite sciurognathous rodents with a hystricomorphous zygomasseteric system restricted to sub-Saharan Africa. Many authors have suggested that the two extant families may be only distantly related, that they belong to separate suborders or infraorders. For example, the Pedetidae are the only family of rodents with multiserial enamel except for the Hystricognathi; this characteristic, the hystricomorphous zygomatic region, a common distribution in southern continents has led many researchers to suggest that the springhares may be allied with hystricognaths. Montgelard et al. 2002 generated some support for Anomaluromorpha in a molecular phylogeny using 12S rRNA and cytochrome b. The suborder Anomaluromorpha contains nine living species in two families.
An additional fossil family belongs to this group. †Parapedetidae Pedetidae - springhare Anomaluridae - scaly-tailed flying squirrels, flying mice The following fossil taxa are sometimes placed in the Anomaluromorpha: †Diatomys †Zegdoumyidae
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
Bats are mammals of the order Chiroptera. Bats are more manoeuvrable than birds, flying with their long spread-out digits covered with a thin membrane or patagium; the smallest bat, arguably the smallest extant mammal, is Kitti's hog-nosed bat, 29–34 mm in length, 15 cm across the wings and 2–2.6 g in mass. The largest bats are the flying foxes and the giant golden-crowned flying fox, Acerodon jubatus, which can weigh 1.6 kg and have a wingspan of 1.7 m. The second largest order of mammals, bats comprise about 20% of all classified mammal species worldwide, with over 1,200 species; these were traditionally divided into two suborders: the fruit-eating megabats, the echolocating microbats. But more recent evidence has supported dividing the order into Yinpterochiroptera and Yangochiroptera, with megabats as members of the former along with several species of microbats. Many bats are insectivores, most of the rest are frugivores. A few species feed on animals other than insects. Most bats are nocturnal, many roost in caves or other refuges.
Bats are present throughout the world, with the exception of cold regions. They are important in their ecosystems for dispersing seeds. Bats provide humans at the cost of some threats. Bat dung has been used as fertiliser. Bats consume insect pests, they are sometimes numerous enough to serve as tourist attractions, are used as food across Asia and the Pacific Rim. They are natural reservoirs such as rabies. In many cultures, bats are popularly associated with darkness, witchcraft and death. An older English name for bats is flittermouse, which matches their name in other Germanic languages, related to the fluttering of wings. Middle English had bakke, most cognate with Old Swedish natbakka, which may have undergone a shift from -k- to -t- influenced by Latin blatta, "moth, nocturnal insect"; the word "bat" was first used in the early 1570s. The name "Chiroptera" derives from Ancient Greek: χείρ – cheir, "hand" and πτερόν – pteron, "wing"; the delicate skeletons of bats do not fossilise well, it is estimated that only 12% of bat genera that lived have been found in the fossil record.
Most of the oldest known bat fossils were very similar to modern microbats, such as Archaeopteropus. The extinct bats Palaeochiropteryx tupaiodon and Hassianycteris kumari are the first fossil mammals whose colouration has been discovered: both were reddish-brown. Bats were grouped in the superorder Archonta, along with the treeshrews and primates. Modern genetic evidence now places bats in the superorder Laurasiatheria, with its sister taxon as Fereuungulata, which includes carnivorans, odd-toed ungulates, even-toed ungulates, cetaceans. One study places Chiroptera as a sister taxon to odd-toed ungulates; the phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision into Megachiroptera and Microchiroptera reflected the view that these groups of bats had evolved independently of each other for a long time, from a common ancestor capable of flight; this hypothesis recognised differences between microbats and megabats and acknowledged that flight has only evolved once in mammals.
Most molecular biological evidence supports the view that bats form a monophyletic group. Genetic evidence indicates that megabats originated during the early Eocene, belong within the four major lines of microbats. Two new suborders have been proposed. Yangochiroptera includes the other families of a conclusion supported by a 2005 DNA study. A 2013 phylogenomic study supported the two new proposed suborders. In the 1980s, a hypothesis based on morphological evidence stated the Megachiroptera evolved flight separately from the Microchiroptera; the flying primate hypothesis proposed that, when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features not shared with Microchiroptera. For example, the brains of megabats have advanced characteristics. Although recent genetic studies support the monophyly of bats, debate continues about the meaning of the genetic and morphological evidence; the 2003 discovery of an early fossil bat from the 52 million year old Green River Formation, Onychonycteris finneyi, indicates that flight evolved before echolocative abilities.
Onychonycteris had claws on all five of its fingers, whereas modern bats have at most two claws on two digits of each hand. It had longer hind legs and shorter forearms, similar to climbing mammals that hang under branches, such as sloths and gibbons; this palm-sized bat had short, broad wings, suggesting that it could not fly as fast or as far as bat species. Instead of flapping its wings continuously while flying, Onychonycteris alternated between flaps and
Pel's flying squirrel
Pel's flying squirrel or Pel's scaly-tailed squirrel is a species of rodent in the family Anomaluridae. It is found in Liberia, Ivory Coast, Ghana, where it lives in lowland tropical rainforests. Pel's flying squirrel is named after Hendrik Pel; the tropical forests of Africa were little explored by Europeans before the nineteenth century. Colugos and flying squirrels had been known from south eastern Asia and gliding marsupials from Australia earlier than this, but the discovery of the scaly-tailed squirrels of equatorial Africa was not made till the 1840s. British zoologist and collector Louis Fraser exploring the Niger basin brought a specimen of Lord Derby's scaly-tailed squirrel back to Britain. Compared to the known flying squirrels, this had two rows of large scales on the underside of the basal part of its tail; the flying membrane stretched from wrist to ankle and was supported by a cartilaginous strip which had its origin at the elbow. The scaly tailed squirrels had an additional membrane extending from the ankle to part-way along the tail, when extended, the membrane formed a straight line from heel to heel.
Ten years a specimen of another species, Pel's flying squirrel, was brought to Europe and showed similar anatomical features. The hands and feet had the digits close together with curved nails; the tail was unusual in that the free part resembled the shape of a feather, with the large cornified scales a prominent feature on the underside. The animal's fur was described without any spines. Pel's flying squirrel is a large species, with a head-and-body length of 400 to 540 mm and a tail of 320 to 550 mm, it weighs between 1,300 to 2,000 g The upper parts are black, with some white patches, while the underparts are white. The margin of the patagium, the membrane joining the wrist with the ankle, is white, that of the uropatagium, joining the ankles and tail, is all white; the ears are of average size and naked, the forefeet are black, the hind feet have white patches and the tail is plume-like. Pel's flying squirrel is native to West Africa where its range includes eastern Liberia, southern Ivory Coast and southwestern Ghana.
It occurs in the tropical rainforest at low altitudes where there are tall, emergent trees and palms trees, in areas with annual precipitation in the range 1,400 to 3,900 millimetres. However, it appreciates separate trees that are not wreathed in lianas, because when it emerges from its den at night, it needs space to glide down to lower levels to feed. Pel's flying squirrel is wholly nocturnal, spending the day in a hole in a tree and only emerging after dark, it feeds on bark, supplemented with fruits and leaves. It occurs in pairs, but as many as six individuals have been found sharing the same nesting site in a tree. If disturbed in its den, this squirrel snaps its teeth and hisses, the sound may be amplified by the acoustics of the hollow tree. Given its large size, bold colouration and aggressive behaviour, this species may be able to drive off potential predators such as birds of prey, small carnivores and primates, compete with hornbills for nest sites; the reproduction of this species is poorly known.
In Ghana, litters seem to occur twice a year, in April and September, with two or three young in each litter four. A copulatory plug is present in the vagina during pregnancy and the young are furred and have their eyes open at birth; the young remain in the nest and both parents bring them food. The tropical forests where this flying squirrel lives are under threat because of timber harvesting and the conversion of the land to agricultural use; the animal is under threat from hunters and is sometimes to be seen on sale as bushmeat in markets. As a secretive, nocturnal species, its population size and natural history are little known, the International Union for Conservation of Nature has been unable to classify its conservation status and has rated it as "data deficient". Dieterlen, F. 2005. Family Anomaluridae. Pp. 1532–1534 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Baltimore: Johns Hopkins University Press