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 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 aardvark is a medium-sized, nocturnal mammal native to Africa. It is the only living species of the order Tubulidentata, although other prehistoric species and genera of Tubulidentata are known. Unlike other insectivores, it has a long pig-like snout, used to sniff out food, it roams over most of the southern two-thirds of the African continent, avoiding areas that are rocky. A nocturnal feeder, it subsists on ants and termites, which it will dig out of their hills using its sharp claws and powerful legs, it digs to create burrows in which to live and rear its young. It receives a "least concern" rating from the IUCN; the aardvark is sometimes colloquially called "African ant bear", "anteater", or the "Cape anteater" after the Cape of Good Hope. The name "aardvark" comes from earlier Afrikaans and means "earth pig" or "ground pig", because of its burrowing habits; the name Orycteropus means burrowing foot, the name afer refers to Africa. The name of the aardvarks's order, comes from the tubule-style teeth.
The aardvark is not related to the pig. The aardvark is not related to the South American anteater, despite sharing some characteristics and a superficial resemblance; the similarities are based on convergent evolution. The closest living relatives of the aardvark are the elephant shrews and golden moles. Along with the sirenians, hyraxes and their extinct relatives, these animals form the superorder Afrotheria. Studies of the brain have shown the similarities with Condylarthra, given the clade's status as a wastebasket taxon it may mean some species traditionally classified as "condylarths" are stem-aardvarks. Based on fossils, Bryan Patterson has concluded that early relatives of the aardvark appeared in Africa around the end of the Paleocene; the ptolemaiidans, a mysterious clade of mammals with uncertain affinities, may be stem-aardvarks, either as a sister clade to Tubulidentata or as a grade leading to true tubulidentates. The first unambiguous tubulidentate was Myorycteropus africanus from Kenyan Miocene deposits.
The earliest example from the genus Orycteropus was Orycteropus mauritanicus, found in Algeria in deposits from the middle Miocene, with an old version found in Kenya. Fossils from the aardvark have been dated to 5 million years, have been located throughout Europe and the Near East; the mysterious Pleistocene Plesiorycteropus from Madagascar was thought to be a tubulidentate, descended from ancestors that entered the island during the Eocene. However, a number of subtle anatomical differences coupled with recent molecular evidence now lead researchers to believe that Plesiorycteropus is a relative of golden moles and tenrecs that achieved an aardvark-like appearance and ecological niche through convergent evolution; the aardvark has seventeen poorly defined subspecies listed: Orycteropus afer afer O. a. adametzi Grote, 1921 O. a. aethiopicus Sundevall, 1843 O. a. angolensis Zukowsky & Haltenorth, 1957 O. a. erikssoni Lönnberg, 1906 O. a. faradjius Hatt, 1932 O. a. haussanus Matschie, 1900 O. a. kordofanicus Rothschild, 1927 O. a. lademanni Grote, 1911 O. a. leptodon Hirst, 1906 O. a. matschiei Grote, 1921 O. a. observandus Grote, 1921 O. a. ruvanensis Grote, 1921 O. a. senegalensis Lesson, 1840 O. a. somalicus Lydekker, 1908 O. a. wardi Lydekker, 1908 O. a. wertheri Matschie, 1898The 1911 Encyclopædia Britannica mentions O. a. capensis or Cape ant-bear from South Africa.
The aardvark is vaguely pig-like in appearance. Its body is stout with a prominently is sparsely covered with coarse hairs; the limbs are with the rear legs being longer than the forelegs. The front feet have lost the pollex; each toe bears a large, robust nail, somewhat flattened and shovel-like, appears to be intermediate between a claw and a hoof. Whereas the aardvark is considered digitigrade, it appears at time to be plantigrade; this confusion happens because. A contributing characteristic to the burrow digging capabilities of aardvarks is an endosteal tissue called compacted coarse cancellous bone; the stress and strain resistance provided by CCCB allows aardvarks to create their burrows leading to a favorable environment for plants and a variety of animals. An aardvark's weight is between 60 and 80 kilograms. An aardvark's length is between 105 and 130 centimetres, can reach lengths of 2.2 metres when its tail is taken into account. It is 60 centimetres tall at the shoulder, has a girth of about 100 centimetres.
It is the largest member of the proposed clade Afroinsectiphilia. The aardvark is pale yellowish-gray in color and stained reddish-brown by soil; the aardvark's coat is thin, the animal's primary protection is its tough skin. Its hair is short on its tail; the hair on the majority of its body is grouped in clusters of 3-4 hairs. The hair surrounding its nostrils is dense to help filter particulate matter out, its tail is thick at the base and tapers. The elongated head is set on a shor
Paenungulata is a clade that groups three extant mammal orders: Proboscidea and Hyracoidea. At least two more orders are known only as fossils, namely Desmostylia; each of these extinct orders was as unique in its members' ways as the surviving orders. Embrithopods were rhinoceros-like herbivorous mammals with plantigrade feet, desmostylians were hippopotamus-like amphibious animals, their walking posture and diet have been the subject of speculation, but tooth wear indicates that desmostylians browsed on terrestrial plants and had a posture similar to other large hoofed mammals. Of the five orders, hyraxes are the most basal, followed by embrithopods; these latter three are grouped as the Tethytheria, because it is believed that their common ancestors lived on the shores of the prehistoric Tethys Sea. Although morphological evidence continues to support the position of paenungulates with the ungulates, the molecular evidence suggests that Paenungulata is part of the cohort Afrotheria, an ancient assemblage of African mammals of great diversity.
The other members of this cohort are the orders Afrosoricida and Tubulidentata. In 1945, George Gaylord Simpson used traditional taxonomic techniques to group these spectacularly diverse mammals in the superorder he named Paenungulata, but there were many loose threads in unravelling their genealogy. For example, hyraxes in his Paenungulata had some characteristics suggesting they might be connected to the odd-toed ungulates. Indeed, early taxonomists placed the Hyracoidea closest to the rhinoceroses, because of their dentition, some recent evidence suggested a possible affinity of Hyracoidea to Perissodactyla rather than to the rest of the Paenungulata. If true, this would mean. Genetic techniques were developed for inspecting amino acid differences among haemoglobin sequences; the most parsimonious cladograms depicted Simpson's Paenungulata as an authentic clade and as one of the first groups to diversify from the basal placental mammals. The amino acid sequences reject a connection with perissodactyls.
Altungulata Meridiungulata Kleinschmidt, Traute. "Paenungulata: A Comparison of the Hemoglobin Sequences from Elephant and Manatee". Mol. Biol. Evol. 3: 427–435. PMID 3444412. Archived from the original on 2010-06-30. Retrieved 2010-07-24. McKenna, M. C. and S. K. Bell. 1997. Classification of Mammals Above the Species Level. New York: Columbia University Press. ISBN 0-231-11013-8 Seiffert, Erik. "A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic and fossil evidence". BMC Evolutionary Biology. 7: 13. Doi:10.1186/1471-2148-7-224. PMC 2248600. PMID 17999766. Simpson, G. G. 1945. "The principles of classification and a classification of mammals", in Bulletin of the American Museum of Natural History 85:1-350. Gheerbrant, E. "Paenungulata". In Kenneth D. Rose, J. David Archibald; the Rise of Placental Mammals: Origins and Relationships of the Major Extant Clades. Baltimore: Johns Hopkins University Press. Pp. 84–105. ISBN 080188022X. Paleos.com: Vertebrates: Paenungulata
Eutheria is one of two mammalian clades with extant members that diverged in the Early Cretaceous or the Late Jurassic. Except for the Virginia opossum, from North America, a metatherian, all post-Miocene mammals indigenous to Europe, Africa and North America north of Mexico are eutherians. Extant eutherians, their last common ancestor, all extinct descendants of that ancestor are members of Placentalia. Eutherians are distinguished from noneutherians by various phenotypic traits of the feet, ankles and teeth. All extant eutherians lack epipubic bones; this allows for expansion of the abdomen during pregnancy. The oldest-known eutherian species is Juramaia sinensis, dated at 161 million years ago from the Jurassic in China. Eutheria was named in 1872 by Theodore Gill. Distinguishing features are: an enlarged malleolus at the bottom of the tibia, the larger of the two shin bones the joint between the first metatarsal bone and the entocuneiform bone in the foot is offset farther back than the joint between the second metatarsal and middle cuneiform bones—in metatherians these joints are level with each other various features of jaws and teeth Eutheria contains several extinct genera as well as larger groups, many with complicated taxonomic histories still not understood.
Members of the Adapisoriculidae and Leptictida have been placed within the out-dated placental group Insectivora, while Zhelestids have been considered primitive ungulates. However, more recent studies have suggested these enigmatic taxa represent stem group eutherians, more basal to Placentalia; the weakly favoured cladogram favours Boreoeuthearia as a basal Eutherian clade as sister to the Atlantogenata
Ptolemaiida is a taxon of wolf-sized afrothere mammals that lived in northern and eastern Africa during the Paleogene. The oldest fossils are from the latest Eocene strata of the Jebel Qatrani Formation, near the Fayum oasis in Egypt. A tooth is known from an Oligocene-aged stratum in Angola, Miocene specimens are known from Kenya and Uganda The origin of the Ptolemaiida is obscure, debated; the type species was thought to be a primate, but when elongated skulls with long canines of Ptolemaia and Qarunavus were found, they were thought to be hyaenodontids, or giant, carnivorous relatives of the pantolestid, of modern shrews The family Ptolemaiidae was elevated to order level in 1995, although some experts placed the Ptolemaiidae within the pantolestids. Ptolemaiida has been placed within Afrotheria on the basis of paleobiology, as the taxon was endemic to Africa, because of some similarities in the anatomical features of the skull in common with aardvarks, it is unclear if they form a sister taxon to Tubulidentata or are a paraphyletic sequence leading to them.
Regardless, their close relation may offer the possibility for true dental synapomorphies in Afroinsectiphilia. As mentioned earlier, there has been much confusion about the origins and identities of the ptolemaiidans; the first specimen, a set of isolated molar teeth, of the type species, Ptolemaia lyonsi, was identified as being a primate, as they were flat and nearly identical to those of primates. When the first skull was found, it was thought to be a monstrous, wolf-sized shrew, as the skull had long canine fangs, was gracile; however there has been a reconsideration of the ptolemaiidan diet, possible behavior, as wear on the teeth suggest that it crushed hard or abrasive food, that the teeth had little or no shearing ability. So, some sources still refer to them as being gigantic, carnivorous shrews
Ungulates are any members of a diverse group of large mammals that includes odd-toed ungulates such as horses and rhinoceroses, even-toed ungulates such as cattle, giraffes, camels and hippopotamuses. Most terrestrial ungulates use the tips of their toes hoofed, to sustain their whole body weight while moving; the term means "being hoofed" or "hoofed animal". As a descriptive term, "ungulate" excludes cetaceans, as they do not possess most of the typical morphological characteristics of ungulates, but recent discoveries indicate that they are descended from early artiodactyls. Ungulates are herbivorous, many employ specialized gut bacteria to allow them to digest cellulose, as in the case of ruminants, they inhabit a wide range of habitats, including jungles and rivers. Ungulata, which used to be considered an order, has been split into the following: Perissodactyla, Tubulidentata, Sirenia and Cetacea. However, in 2009 morphological and molecular work has found that aardvarks, sea cows, elephants are more related to sengis and golden moles than to the perissodactyls and artiodactyls, form Afrotheria.
Elephants, sea cows, hyraxes are grouped together in the clade Paenungulata, while the aardvark has been considered as either a close relative to them or a close relative to sengis in the clade Afroinsectiphilia. This is a striking example of convergent evolution. There is now some dispute as to whether this smaller Ungulata is a cladistic group, or a phenetic group or folk taxon; some studies have indeed found the mesaxonian ungulates and paraxonian ungulates to form a monophyletic lineage related to either the Ferae in the clade Fereuungulata or to the bats. Other studies found the two orders not that related, as some place the perissodactyls as close relatives to bats and Ferae in Pegasoferae and others place the artiodactyls as close relatives to bats. Below is a simplified taxonomy with the extant families, in order of the relationships. Keep in mind that there are still some grey areas of conflict, such as the case with relationship of the pecoran families and the baleen whale families.
See each family for the relationships of the species as well as the controversies in their respective article. Ungulata Perissodactyla Hippomorpha Equidae: Horses and zebras Ceratomorpha Tapiridae: Tapirs Rhinocerotidae: Rhinoceroses Artiodactyla Tylopoda Camelidae: Camels and Llamas Artiofabula Suina Tayassuidae: Peccaries Suidae: Pigs Cetruminantia Ruminantia Tragulidae: Chevrotains Cervoidea Antilocapridae: Pronghorn Giraffidae: Giraffes and okapi Cervidae: Deer Moschidae: Musk deer Bovidae: Oxen and antelopes Whippomorpha Hippopotamidae: Hippopotamuses Cetacea Mysticeti Balaenidae: Bowhead and right whales Cetotheriidae: Pygmy right whale Eschrichtiidae: Gray Whale Balaenopteridae: Rorquals Odontoceti Physeteroidea Physeteridae: Sperm whale Kogiidae: Lesser sperm whales Platanistoidea Platanistidae: Indian river dolphins Ziphioidea Ziphiidae: Beaked whales Lipotoidea Lipotidae: Baiji Inioidea Iniidae: Amazonian river dolphins Pontoporiidae: La Plata dolphin Delphinoidea Monodontidae: Beluga and narwhal Phocoenidae: Porpoises Delphinidae: Oceanic dolphins Below is the general consensus of the phylogeny of the ungulate families.
Perissodactyla and Artiodactyla include the majority of large land mammals. These two groups first appeared during the late Paleocene spreading to a wide variety of species on numerous continents, have developed in parallel since that time; some scientists believed that modern ungulates are descended from an evolutionary grade of mammals known as the condylarths. The enigmatic dinoceratans were among the first large herbivorous mammals, although their exact relationship with other mammals is still debated with one of the theories being that they might just be distant relatives to living ungulates. In Australia, the marsupial Chaeropus developed hooves, convergent those of artiodactyls. Perissodactyls are said to have evolved from the Phenacodontidae, sheep-sized animals that were showing signs of anatomical features that their descendants would inherit. By the start of the Eocene, 55 million years ago, they had diversified and spread out to occupy several continents. Horses and tapirs both evolved in North America.
Of the 15 families, only three survive. These families were diverse in form and size; the largest perissodactyl, an Asian rhinoceros called Paraceratherium, reached 15 tonnes, more than twice the weight of an elephant. It has been found