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 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
Wikispecies is a wiki-based online project supported by the Wikimedia Foundation. Its aim is to create a comprehensive free content catalogue of all species. Jimmy Wales stated that editors are not required to fax in their degrees, but that submissions will have to pass muster with a technical audience. Wikispecies is available under the GNU Free Documentation License and CC BY-SA 3.0. Started in September 2004, with biologists across the world invited to contribute, the project had grown a framework encompassing the Linnaean taxonomy with links to Wikipedia articles on individual species by April 2005. Benedikt Mandl co-ordinated the efforts of several people who are interested in getting involved with the project and contacted potential supporters in early summer 2004. Databases were evaluated and the administrators contacted, some of them have agreed on providing their data for Wikispecies. Mandl defined two major tasks: Figure out how the contents of the data base would need to be presented—by asking experts, potential non-professional users and comparing that with existing databases Figure out how to do the software, which hardware is required and how to cover the costs—by asking experts, looking for fellow volunteers and potential sponsorsAdvantages and disadvantages were discussed by the wikimedia-I mailing list.
The board of directors of the Wikimedia Foundation voted by 4 to 0 in favor of the establishment of a Wikispecies. The project is hosted at species.wikimedia.org. It was merged to a sister project of Wikimedia Foundation on September 14, 2004. On October 10, 2006, the project exceeded 75,000 articles. On May 20, 2007, the project exceeded 100,000 articles with a total of 5,495 registered users. On September 8, 2008, the project exceeded 150,000 articles with a total of 9,224 registered users. On October 23, 2011, the project reached 300,000 articles. On June 16, 2014, the project reached 400,000 articles. On January 7, 2017, the project reached 500,000 articles. On October 30, 2018, the project reached 600,000 articles, a total of 1.12 million pages. Wikispecies comprises taxon pages, additionally pages about synonyms, taxon authorities, taxonomical publications, institutions or repositories holding type specimen. Wikispecies asks users to use images from Wikimedia Commons. Wikispecies does not allow the use of content.
All Species Foundation Catalogue of Life Encyclopedia of Life Tree of Life Web Project List of online encyclopedias The Plant List Wikispecies, The free species directory that anyone can edit Species Community Portal The Wikispecies Charter, written by Wales
The Saxifragales are an order of flowering plants. Their closest relatives are a large eudicot group known as the rosids by the definition of rosids given in the APG II classification system; some authors define the rosids more including Saxifragales as their most basal group. Saxifragales is one of the eight groups; the others are Gunnerales, Rosids, Berberidopsidales and Asterids. Saxifragales have an extensive fossil record; the extant members are remnants of a diverse and widespread order. The Saxifragales order, as it is now understood, is based upon the results of molecular phylogenetic studies of DNA sequences, it is not part of any of the classification systems based on plant morphology. The group is much in need of comparative anatomical study in light of the recent expansion of the family Peridiscaceae to include Medusandra, a genus that before 2009 had not been placed in Saxifragales; the order is divided into suprafamilial groups. These groups are not understood to have any particular taxonomic rank.
Saxifragales contain about 2470 species. These are distributed into 15 families, or into 12 families if Haloragaceae sensu lato is recognized as a family consisting of Haloragaceae sensu stricto, Penthorum and Aphanopetalum. About 95% of the species are in five families: Crassulaceae, Grossulariaceae and Hamamelidaceae. Most of the families are monogeneric; the number of genera in each family is: Some authors do not recognize Choristylis as a separate genus from Itea. Some authors sink Liquidambar and Semiliquidambar into Altingia, thus Altingiaceae and Iteaceae are monogeneric in some classifications. Within the Saxifragales is a suprafamilial group known as the Saxifragaceae alliance, it comprises four families: Pterostemonaceae, Iteaceae and Saxifragaceae. These have long been known to be related to each other, but the circumscription of Saxifragaceae has changed dramatically, it is now a much smaller family. Crassulaceae and Tetracarpaeaceae have long been associated with Saxifragaceae. Penthorum has been associated with Crassulaceae, but sometimes with Saxifragaceae.
Two members of the core Saxifragales had sometimes been placed near Saxifragaceae, but elsewhere. Aphanopetalum was placed in Cunoniaceae, a family in Oxalidales though there were good reasons to put it in Saxifragales. Aphanopetalum is now excluded from Cunoniaceae. Haloragaceae was thought to be a family in Myrtales, but it is no longer included in that order. Cercidiphyllaceae had for a long time been associated with Hamamelidaceae and Trochodendraceae and was thought to be closer to the latter. Cercidiphyllaceae is now known to be a member of the woody clade of Saxifragales, along with Hamamelidaceae and Daphniphyllaceae, but Trochodendraceae is in the basal eudicot order Trochodendrales. Altingiaceae was not separated from Hamamelidaceae until phylogenetic studies showed that its inclusion might make Hamamelidaceae paraphyletic; the recognition of Altingiaceae as a separate family received strong statistical support in 2008. Daphniphyllum was always thought to have an anomalous combination of characters and it was placed in several different orders before molecular phylogenetic analysis showed it to belong to Saxifragales.
Paeoniaceae possesses many unique features and its taxonomic position was for a long time controversial. The idea has long persisted. Paeoniaceae has been shown unequivocally to belong in Saxifragales, while Glaucidium is in the family Ranunculaceae; the family Peridiscaceae underwent radical shifting and recircumscription from 2003 to 2009. It consisted of two related genera and Whittonia; the APG II system placed the family in Malpighiales, based on a DNA sequence for the rbcL gene from Whittonia. This sequence turned out to be not from Whittonia, but from other plants whose DNA had contaminated the sample. After Peridiscaceae was placed in Saxifragales, it was expanded to include Soyauxia in 2007, expanded again to include Medusandra in 2009; the phylogeny shown below is based on the one published by Shuguang Jian and coauthors in 2008. All branches have 100% maximum likelihood bootstrap support except where labeled with bootstrap percentage. Monogeneric families are represented by genus names.
Plant order classification at: Saxifragales Trees At: Angiosperm Phylogeny Website At: Missoure Botanical Garden Website Saxifragales At: Angiosperm Phylogeny Website Wurdack, Kenneth J.. "Malpighiales phylogenetics: Gaining ground on one of the most recalcitrant clades in the angiosperm tree of life". American Journal of Botany. 96: 1551–70. Doi:10.3732/ajb.0800207. PMID 21628300. Jian, Shuguang. "Resolving an ancient, rapid radiation in Saxifragales". Systematic Biology. 57: 38–57. Doi:10.1080/10635150801888871. PMID 18275001. Kubitzki, Klaus, ed.. Flowering Plants. Eudicots: Berberidopsidales, Crossosomatales, Fabales p.p. Geraniales, Myrtales p.p. Proteales, Vitales, Clusiaceae Alliance, Passifloraceae Alliance, Huaceae, Sabiaceae; the Families and Genera of Vascular Plants. IX. Springer. ISBN 978-3-540-32219-1
Crossosomataceae is a small plant family, consisting of three genera of shrubs found only in the dry parts of the American southwest and Mexico. This family includes ten known species. Apacheria - one species, cliff brittlebush, Apacheria chiricahuensis Crossosoma - crossosoma Glossopetalon - glossopetalon Velascoa - one species
The Cronquist system is a taxonomic classification system of flowering plants. It was developed by Arthur Cronquist in a series of monographs and texts, including The Evolution and Classification of Flowering Plants and An Integrated System of Classification of Flowering Plants. Cronquist's system places flowering plants into two broad classes and Liliopsida. Within these classes, related orders are grouped into subclasses. While the scheme was used, in either the original form or in adapted versions, many botanists now use the Angiosperm Phylogeny Group classification for the orders and families of flowering plants, first developed in 1998; the system as laid out in Cronquist's An Integrated System of Classification of Flowering Plants counts 64 orders and 321 families in class Magnoliopsida and 19 orders and 65 families in class Liliopsida. Class Liliatae Subclass Alismatidae 4 orders Order Alismatales... Order Triuridales Subclass Commelinidae 8 orders Order Commelinales... Order Zingiberales Subclass Arecidae 4 orders Order Arecales...
Order Arales Subclass Liliidae 2 orders Order Liliales Family Philydraceae Family Pontederiaceae Family Liliaceae Family Iridaceae Family Agavaceae Family Xanthorrhoeaceae Family Velloziaceae Family Haemodoraceae Family Taccaceae Family Cyanastraceae Family Stemonaceae Family Smilacaceae Family Dioscoreaceae Order Orchidales Subclass Magnoliidae Order Magnoliales Winteraceae Degeneriaceae Himantandraceae Eupomatiaceae Austrobaileyaceae Magnoliaceae Lactoridaceae Annonaceae Myristicaceae Canellaceae Order Laurales Amborellaceae Trimeniaceae Monimiaceae Gomortegaceae Calycanthaceae Idiospermaceae Lauraceae Hernandiaceae Order Piperales Chloranthaceae Saururaceae Piperaceae Order Aristolochiales Aristolochiaceae Order Illiciales Illiciaceae Schisandraceae Order Nymphaeales Nelumbonaceae Nymphaeaceae Barclayaceae Cabombaceae Ceratophyllaceae Order Ranunculales Ranunculaceae Circaeasteraceae Berberidaceae Sargentodoxaceae Lardizabalaceae Menispermaceae Coriariaceae Sabiaceae Order Papaverales Papaveraceae Fumariaceae Subclass Hamamelidae Order Trochodendrales Tetracentraceae Trochodendraceae Order Hamamelidales Cercidiphyllaceae Eupteleaceae Platanaceae Hamamelidaceae Myrothamnaceae Order Daphniphyllales Daphniphyllaceae Order Didymelales Didymelaceae Order Eucommiales Eucommiaceae Order Urticales Barbeyaceae Ulmaceae Cannabaceae Moraceae Cecropiaceae Urticaceae Order Leitneriales Leitneriaceae Order Juglandales Rhoipteleaceae Juglandaceae Order Myricales Myricaceae Order Fagales Balanopaceae Ticodendraceae Fagaceae Nothofagaceae Betulaceae Order Casuarinales Casuarinaceae Subclass Caryophyllidae Order Caryophyllales Phytolaccaceae Achatocarpaceae Nyctaginaceae Aizoaceae Didiereaceae Cactaceae Chenopodiaceae Amaranthaceae Portulacaceae Basellaceae Molluginaceae Caryophyllaceae Order Polygonales Polygonaceae Order Plumbaginales Plumbaginaceae Subclass Dilleniidae Order Dilleniales Dilleniaceae Paeoniaceae Order Theales Ochnaceae Sphaerosepalaceae Sarcolaenaceae Dipterocarpaceae Caryocaraceae Theaceae Actinidiaceae Scytopetalaceae Pentaphylacaceae Tetrameristaceae Pellicieraceae Oncothecaceae Marcgraviaceae Quiinaceae Elatinaceae Paracryphiaceae Medusagynaceae Clusiaceae Order Malvales Elaeocarpaceae Tiliaceae Sterculiaceae Bombacaceae Malvaceae Order Lecythidales Lecythidaceae Order Nepenthales Sarraceniaceae Nepenthaceae Droseraceae Order Violales Flacourtiaceae Peridiscaceae Bixaceae Cistaceae Huaceae Lacistemataceae Scyphostegiaceae Stachyuraceae Violaceae Tamaricaceae Frankeniaceae Dioncophyllaceae Ancistrocladaceae Turneraceae Malesherbiaceae Passifloraceae Achariaceae Caricaceae Fouquieriaceae Hoplestigmataceae Cucurbitaceae Datiscaceae Begoniaceae Loasaceae Order Salicales Salicaceae Order Capparales Tovariaceae Capparaceae Brassicaceae Moringaceae Resedaceae Order Batales Gyrostemonaceae Bataceae Order Ericales Cyrillaceae Clethraceae Grubbiaceae Empetraceae Epacridaceae Ericaceae Pyrolaceae Monotropaceae Order Diapensiales Diapensiaceae Order Ebenales Sapotaceae Ebenaceae Styracaceae Lissocarpaceae Symplocaceae Order Primulales Theophrastaceae Myrsinaceae Primulaceae Subclass Rosidae Order Rosales Brunelliaceae Connaraceae Eucryphiaceae Cunoniaceae Davidsoniaceae Dialypetalanthaceae Pittosporaceae Byblidaceae Hydrangeaceae Columelliaceae Grossulariaceae Greyiaceae Bruniaceae Anisophylleaceae Alseuosmiaceae Crassulaceae Cephalotaceae Saxifragaceae Rosaceae Neuradaceae Crossosomataceae Chrysobalanaceae Surianaceae Rhabdodendraceae Order Fabales Mimosaceae Caesalpiniaceae Fabaceae Order Proteales Elaeagnaceae Proteaceae Order Podostemales Podostemaceae Order Haloragales Haloragaceae Gunneraceae Order Myrtales Sonneratiaceae Lythraceae Penaeaceae Crypteroniaceae Thymelaeaceae Trapaceae Myrtaceae Punicaceae Onagraceae Oliniaceae Melastomataceae Combretaceae Alzateaceae Memecylaceae Rhyncocalycaceae Order Rhizophorales Rhizophoraceae Order Cornales Alangiaceae Nyssaceae Cornaceae Garryaceae Order Santalales Medusandraceae Dipentodontaceae Olacaceae Opiliaceae Santalaceae Misodendraceae Loranthaceae Viscaceae Eremolepidaceae Balanophoraceae Order Rafflesiales Hydnoraceae Mitrastemonaceae Rafflesiaceae Order Celastrales Geissolomataceae Celastraceae Hippocrateaceae Stackhousiaceae Salvadoraceae Aquifoliaceae Icacinaceae Aextoxicaceae Cardiopteridaceae Corynocarpaceae Dichapetalaceae Tepuianthaceae Order Euphorbiales Buxaceae Simmondsiaceae Pandaceae Euphorbiaceae Order Rhamnales Rhamnaceae Leeaceae Vitaceae Order Linales Erythroxylaceae Humiriaceae Ixonanthaceae Hugoniaceae Linaceae Order Polygalales Malpighiaceae Vochysiaceae Trig
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