The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma. The Coniacian is followed by the Santonian; the Coniacian is named after the city of Cognac in the French region of Saintonge. It was first defined by French geologist Henri Coquand in 1857; the base of the Coniacian stage is at the first appearance of the inoceramid bivalve species Cremnoceramus rotundatus. An official reference profile for the base had in 2009 not yet been appointed; the top of the Coniacian is defined by the appearance of the inoceramid bivalve Cladoceramus undulatoplicatus. The Coniacian overlaps the regional Emscherian stage of Germany, coeval with the Coniacian and Santonian stages. In magnetostratigraphy, the Coniacian is part of magnetic chronozone C34, the so-called Cretaceous Magnetic Quiet Zone, a long period with normal polarity. After a maximum of the global sea level during the early Turonian, the Coniacian was characterized by a gradual fall of the sea level.
This cycle is in sequence stratigraphy seen as a first order cycle. During the middle Coniacian a shorter, second order cycle, caused a temporary rise of the sea level on top of the longer first order trend; the following regression separates the Middle from the Upper Coniacian substage. An shorter third order cycle caused a new transgression during the Late Coniacian. Beginning in the Middle Coniacian, an anoxic event occurred in the Atlantic Ocean, causing large scale deposition of black shales in the Atlantic domain; the anoxic event lasted till the Middle Santonian and is the longest and last such event during the Cretaceous period. The Coniacian is subdivided into Lower and Upper substages, it encompasses three ammonite biozones in the Tethys domain: zone of Paratexanites serratomarginatus zone of Gauthiericeras margae zone of Peroniceras tridorsatumIn the boreal domain the Coniacian overlaps just one ammonite biozone: that of Forresteria petrocoriensis Gradstein, F. M.. G. & Smith, A. G.. Meyers, P.
A.. M. & Forster, A.. GeoWhen Database - Coniacian Late Cretaceous timescale, at the website of the subcommission for stratigraphic information of the ICS Stratigraphic chart of the Late Cretaceous, at the website of Norges Network of offshore records of geology and stratigraphy
The Paleocene or Palaeocene, the "old recent", is a geological epoch that lasted from about 66 to 56 million years ago. It is the first epoch of the Paleogene Period in the modern Cenozoic Era; as with many geologic periods, the strata that define the epoch's beginning and end are well identified, but the exact ages remain uncertain. The Paleocene Epoch is bracketed by two major events in Earth's history, it started with the mass extinction event at the end of the Cretaceous, known as the Cretaceous–Paleogene boundary. This was a time marked by the demise of non-avian dinosaurs, giant marine reptiles and much other fauna and flora; the die-off of the dinosaurs left unfilled ecological niches worldwide. The Paleocene ended with the Paleocene–Eocene Thermal Maximum, a geologically brief interval characterized by extreme changes in climate and carbon cycling; the name "Paleocene" comes from Ancient Greek and refers to the "old" "new" fauna that arose during the epoch. The K–Pg boundary that marks the separation between Cretaceous and Paleocene is visible in the geological record of much of the Earth by a discontinuity in the fossil fauna and high iridium levels.
There is fossil evidence of abrupt changes in flora and fauna. There is some evidence that a substantial but short-lived climatic change may have happened in the early decades of the Paleocene. There are several theories about the cause of the K–Pg extinction event, with most evidence supporting the impact of a 10 km diameter asteroid forming the buried Chicxulub crater on the coast of Yucatan, Mexico; the end of the Paleocene was marked by a time of major change, one of the most significant periods of global change during the Cenozoic. The Paleocene–Eocene Thermal Maximum upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and a major turnover in mammals on land; the Paleocene is divided into three stages, the Danian, the Selandian and the Thanetian, as shown in the table above. Additionally, the Paleocene is divided into six Mammal Paleogene zones; the early Paleocene was cooler and drier than the preceding Cretaceous, though temperatures rose during the Paleocene–Eocene Thermal Maximum.
The climate became warm and humid worldwide towards the Eocene boundary, with subtropical vegetation growing in Greenland and Patagonia, crocodilians swimming off the coast of Greenland, early primates evolving in the tropical palm forests of northern Wyoming. The Earth's poles were temperate. In many ways, the Paleocene continued processes. During the Paleocene, the continents continued to drift toward their present positions. Supercontinent Laurasia had not yet separated into three continents - Europe and Greenland were still connected, North America and Asia were still intermittently joined by a land bridge, while Greenland and North America were beginning to separate; the Laramide orogeny of the late Cretaceous continued to uplift the Rocky Mountains in the American west, which ended in the succeeding epoch. South and North America remained separated by equatorial seas. Africa was heading north towards Europe closing the Tethys Ocean, India began its migration to Asia that would lead to a tectonic collision and the formation of the Himalayas.
The inland seas in North America and Europe had receded by the beginning of the Paleocene, making way for new land-based flora and fauna. Warm seas circulated including the poles; the earliest Paleocene featured a low diversity and abundance of marine life, but this trend reversed in the epoch. Tropical conditions gave rise including coral reefs. With the demise of marine reptiles at the end of the Cretaceous, sharks became the top predators. At the end of the Cretaceous, the ammonites and many species of foraminifera became extinct. Marine fauna came to resemble modern fauna, with only the marine mammals and the Carcharhinid sharks missing. Terrestrial Paleocene strata overlying the K–Pg boundary is in places marked by a "fern spike": a bed rich in fern fossils. Ferns are the first species to colonize areas damaged by forest fires. In general, the Paleocene is marked by the development of modern plant species. Cacti and palm trees appeared. Paleocene and plant fossils are attributed to modern genera or to related taxa.
The warm temperatures worldwide gave rise to thick tropical, sub-tropical and deciduous forest cover around the globe with ice-free polar regions covered with coniferous and deciduous trees. With no large browsing dinosaurs to thin them, Paleocene forests were denser than those of the Cretaceous. Flowering plants, first seen in the Cretaceous, continued to develop and proliferate, along with them coevolved the insects that fed on these plants and pollinated them. Mammals had first appeared in the Late Triassic, evolving from advanced cynodonts, developed alongside the dinosaurs, exploiting ecological niches untouched by the larger and more famous Mesozoic animals: in the insect-rich fo
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 113.0 ± 1.0 Ma, approximately. The Aptian precedes the Albian, all part of the Lower/Early Cretaceous; the Aptian overlaps the upper part of the regionally used stage Urgonian. The Selli Event known as OAE1a, was one of two oceanic Anoxic events in the Cretaceous period, which occurred around 120 Ma and lasted 1 to 1.3 million years. The Aptian extinction was a minor extinction event hypothesized to have occurred around 116 to 117 Ma; the Aptian was named after the small city of Apt in the Provence region of France, known for its crystallized fruits. The original type locality is in the vicinity of Apt; the Aptian was introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1840. The base of the Aptian stage is laid at magnetic anomaly M0r. A global reference profile for the base had in 2009 not yet been appointed.
The top of the Aptian is at the first appearance of coccolithophore species Praediscosphaera columnata in the stratigraphic record. In the Tethys domain, the Aptian contains eight ammonite biozones: zone of Hypacanthoplites jacobi zone of Nolaniceras nolani zone of Parahoplites melchioris zone of Epicheloniceras subnodosocostatum zone of Duffrenoyia furcata zone of Deshayesites deshayesi zone of Deshayesites weissi zone of Deshayesites oglanlensisSometimes the Aptian is subdivided in three substages or subages: Bedoulian and Clansayesian. Examples of rock units formed during the Aptian are: Antlers Formation, Cedar Mountain Formation, Cloverly Formation, Elrhaz Formation, Jiufotang Formation, Little Atherfield, Mazong Shan, Potomac Formation, Santana Formation, Twin Mountains Formation, Xinminbao Group and Yixian Formation. Eogaudryceras Georgioceras Lithancylus Pictetia Salfeldiella Zuercherella Lower Ammonitoceras Australiceras Cheloniceras Cicatrites Colombiceras Dufrenoya Eotetragonites Helicancylus Melchiorites Parahoplites Procheloniceras Prodeshayesites Pseudosaynella Roloboceras Shastoceras Upper Acanthohoplites Acanthoplites Ammonoceratites Argonauticeras Beudanticeras Burckhardites Cloioceras Desmoceras Diadochoceras Diodochoceras Eodouvilleiceras Epancyloceras Epicheloniceras Gabbioceras Gargasiceras Gyaloceras Hamites Hulenites Hypacanthoplites Jauberticeras Kazanskyella Knemiceras Mathoceras Mathoceratites Megatyloceras Metahamites Miyakoceras Neosilesites Nodosohoplites Nolaniceras Protacanthoplites Protanisoceras Sinzovia Somalites Tetragonites Theganoceras Trochleiceras Tropaeum Uhligella Conoteuthis Vectibelus Lower Parahibolites Peratobelus Tetrabelus Carinonautilus Heminautilus Upper Zhuralevia Upper Euphylloceras Upper Adygeya Naefia Boluochia zhengi Changchengornis hengdaoziensis Chaoyangia beishanensis Confuciusornis sanctus Cuspirostrisornis houi Jeholornis prima Jixiangornis orientalis Largirostrornis sexdentoris Longchengornis sanyanensis Longipteryx chaoyangensis Sapeornis chaoyangensis Sinornis santensis/Cathayornis yandica Songlingornis linghensis Yanornis martini Yixianornis grabaui Sarcosuchus Hybodus Jinanichthys longicephalus Lycoptera davidi Lycoptera muroii Peipiaosteus pani Protosephurus liui Sinamia zdanskyi Amblydectes Anhanguera Araripedactylus dehmi Araripesaurus castilhoi Arthurdactylus conandoylei Boreopterus cuiae Brasileodactylus araripensis Cearadactylus atrox Chaoyangopterus zhangi Dsungaripterus weii Dsungaripterus brancai Eoazhdarcho liaoxiensis Eopteranodon lii Gegepterus changi Haopterus gracilis Hongshanopterus lacustris Huaxiapterus benxiensis Huaxiapterus corollatus Huaxiapterus jii Istiodactylus latidens Istiodactylus sinensis Jidapterus edentus Liaoningopterus gui Liaoxipterus brachyognathus Lonchodectes Longchengpterus zhaoi Ludodactylus sibbicki Nemicolopterus crypticus Nurhachius ignaciobritoi Ornithocheirus simus Ornithocheirus mesembrinus Pricesaurus megalodon Santanadactylus Sinopterus dongi Sinopterus gui Tapejara navigans Tapejara wellnhoferi Thalassodromeus sethi Tropeognathus mesembrinus Tropeognathus robustus Tupandactylus imperator Aptian extinction Gradstein, F.
M.. G. & Smith, A. G.. D'Orbigny, A. C. V. M.. GeoWhen Database - Aptian Mid-Cretaceous timescale, at the website of the subcommission for stratigraphic information of the ICS Stratigraphic charts of the Lower Cretaceous: and, at the website of Norges Network of offshore records of geology and stratigraphy
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs that thrived in what are now North America and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 155.7 million years ago. The last ceratopsian species, Triceratops prorsus, became extinct during the Cretaceous–Paleogene extinction event, 66 million years ago. Early members of the ceratopsian group, such as Psittacosaurus, were small bipedal animals. Members, including ceratopsids like Centrosaurus and Triceratops, became large quadrupeds and developed elaborate facial horns and frills extending over the neck. While these frills might have served to protect the vulnerable neck from predators, they may have been used for display, the attachment of large neck and chewing muscles or some combination of the above. Ceratopsians ranged in size from 23 kilograms to over 9 meters and 9,100 kg. Triceratops is by far the best-known ceratopsian to the general public.
It is traditional for ceratopsian genus names to end in "-ceratops", although this is not always the case. One of the first named genera was Ceratops itself, which lent its name to the group, although it is considered a nomen dubium today as its fossil remains have no distinguishing characteristics that are not found in other ceratopsians. Ceratopsians are recognized by features of the skull. On the tip of a ceratopsian upper jaw is the rostral bone, an edentulous ossification, unique to ceratopsians. Othniel Charles Marsh recognized and named this bone, which acts as a mirror image of the predentary bone on the lower jaw; this ossification evolved to morphologically aid the mastication of plant matter. Along with the predentary bone, which forms the tip of the lower jaw in all ornithischians, the rostral forms a superficially parrot-like beak; the jugal bones below the eye are prominent, flaring out sideways to make the skull appear somewhat triangular when viewed from above. This triangular appearance is accentuated in ceratopsians by the rearwards extension of the parietal and squamosal bones of the skull roof, to form the neck frill.
The epoccipital is a distinctive bone found lining the frills of ceratopsians. The name is a misnomer. Epoccipitals begin as separate bones that fuse during the animal's growth to either the squamosal or parietal bones that make up the base of the frill; these bones were ornamental instead of functional, may have helped differentiate species. Epoccipitals were present in all known ceratopsids with the possible exception of Zuniceratops, they appear to have been broadly different between short-frilled ceratopsids and long-frilled ceratopsids, being elliptical with constricted bases in the former group, triangular with wide bases in the latter group. Within these broad definitions, different species would have somewhat different numbers. In centrosaurines like Centrosaurus and Styracosaurus, these bones become long and spike- or hook-like. A well-known example is the coarse sawtooth fringe of broad triangular epoccipitals on the frill of Triceratops; when regarding the ossification's morphogenetic traits, it can be described as dermal.
The term epoccipital was coined by famous paleontologist Othniel Charles Marsh in 1889. The first ceratopsian remains known to science were discovered during the U. S. Geological and Geographical Survey of the Territories led by the American geologist F. V. Hayden. Teeth discovered during an 1855 expedition to Montana were first assigned to hadrosaurids and included within the genus Trachodon, it was not until the early 20th century. During another of Hayden's expeditions in 1872, Fielding Bradford Meek found several giant bones protruding from a hillside in southwestern Wyoming, he alerted paleontologist Edward Drinker Cope. Cope recognized the remains as a dinosaur, but noted that though the fossil lacked a skull, it was different from any type of dinosaur known, he named the new species Agathaumas sylvestris, meaning "marvellous forest-dweller". Soon after, Cope named two more dinosaurs that would come to be recognized as ceratopsids: Polyonax and Monoclonius. Monoclonius was notable for the number of disassociated remains found, including the first evidence of ceratopsid horns and frills.
Several Monoclonius fossils were found by Cope, assisted by Charles Hazelius Sternberg, in summer 1876 near the Judith River in Chouteau County, Montana. Since the ceratopsians had not been recognised yet as a distinctive group, Cope was uncertain about much of the fossil material, not recognizing the nasal horn core, nor the brow horns, as part of a fossil horn; the frill bone was interpreted as a part of the breastbone. In 1888 and 1889, Othniel Charles Marsh described the first well preserved horned dinosaurs and Triceratops. In 1890 Marsh classified them together in the order Ceratopsia; this prompted Cope to reexamine his own specimens and to realize that Triceratops and Agathaumas all represented a single group of similar dinosaurs, which he named Agathaumidae in 1891. Cope redescribed Monoclonius as a horned dinosaur, with a large nasal horn and two smaller horns over the eyes, a large frill. Ceratopsia was coined by Othniel Charles Marsh in 1890 to include dinosaurs possessing certain characteristic features, including horns, a rostral bone, teeth with two roots, fused neck vertebrae, a forward-oriented pubis.
The Maastrichtian is, in the ICS geologic timescale, the latest age of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, of the Mesozoic era or erathem. It spanned the interval from 72.1 to 66 million years ago. The Maastrichtian was succeeded by the Danian. At the end of this period, there was a mass extinction known as the Cretaceous–Paleogene extinction event. At this extinction event, many recognized groups such as non-avian dinosaurs and mosasaurs, as well as many other lesser-known groups, died out; the cause of the extinction is most linked to an asteroid about 10 to 15 kilometres wide colliding with Earth at the end of the Cretaceous. The Maastrichtian was introduced into scientific literature by Belgian geologist André Hubert Dumont in 1849, after studying rock strata of the Chalk Group close to the Dutch city of Maastricht; these strata are now classified as the Maastricht Formation - both formation and stage derive their names from the city. The Maastricht Formation is known for its fossils from this age, most notably those of the giant sea reptile Mosasaurus, which in turn derives its name from the Dutch city.
The base of the Maastrichtian stage is at the first appearance of ammonite species Pachydiscus neubergicus. At the original type locality near Maastricht, the stratigraphic record was found to be incomplete. A reference profile for the base was appointed in a section along the Ardour river called Grande Carrière, close to the village of Tercis-les-Bains in southwestern France; the top of the Maastrichtian stage is defined to be at the iridium anomaly at the Cretaceous–Paleogene boundary, characterised by the extinction of many groups of life, such as certain foraminifers and calcareous nanoplankton, all ammonites and belemnites, etc. The Maastrichtian is subdivided into two substages and three ammonite biozones; the biozones are: zone of Anapachydiscus terminus zone of Anapachydiscus fresvillensis zone of Pachydiscus neubergicus till Pachydiscus epiplectusThe Maastrichtian is coeval with the Lancian North American Land Mammal Age. The following are summaries of the characteristics of specific Maastrichtian aged formations.
The Bearpaw Formation called the Bearpaw Shale, is a sedimentary rock formation found in northwestern North America. It is exposed in the U. S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, east of the Rocky Mountains. It overlies the older Two Medicine, Judith River and Dinosaur Park Formations, is in turn overlain by the Horseshoe Canyon Formation in Canada and the Fox Hills Sandstone in Montana. To the east and south it blends into the Pierre Shale. A marine formation composed of shale, it represents the last major expansion of the Western Interior Seaway before it receded from northwestern North America by the end of the Cretaceous Period, it includes well-preserved ammonite fossils. Other fossils found in this formation include many types of shellfish, bony fish, rays and marine reptiles like mosasaurs and sea turtles; the occasional dinosaur remains have been discovered from carcasses washed out to sea. The Hell Creek Formation is an intensely studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana.
The Hell Creek Formation occurs in badlands of eastern Montana and portions of North Dakota, South Dakota, Wyoming. In Montana, the Hell Creek Formation overlies the Fox Hills Formation and is the uppermost formation of the Cretaceous period, it is a series of fresh and brackish-water clays and sandstones deposited during the Maastrichtian, the last part of the Cretaceous period, by fluvial activity in fluctuating river channels and deltas and occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The climate was mild; the iridium-enriched Cretaceous–Paleogene boundary, which separates the Cretaceous from the Cenozoic, occurs as a discontinuous but distinct thin marker bedding within the Formation, near its uppermost strata. The Horseshoe Canyon Formation is up to 230 m in depth, it is Late Campanian to Early Maastrichtian in age and is composed of mudstone and carbonaceous shales. There are a variety of environments.
The Horseshoe Canyon Formation outcrops extensively in the area of Drumheller, Alberta, as well as further north along the Red Deer River near Trochu, in the city of Edmonton. The Sarir field was discovered in southern Cyrenaica during 1961 and is considered to be the largest oil field in Libya, with estimated oil reserves of 12 Gbbl. Sarir is operated by the Arabian Gulf Oil Company, a subsidiary of the state-owned National Oil Corporation; the Sarir stratigraphic column resembles succession patterns throughout the Sirte Basin, with some variations. In the early regressive phase, basal sandstones were deposited on a Precambrian basement of igneous and metamorphic rocks. Sandstones are dated on angiosperm pollen as younger than Albian from the Late Cretaceous. After a lengthy hiatus, represented by unconformity and sandstone erosion, a transgressive sequence of red and purple Anhydrite shales was laid. Variegated bed remnants occur in crestal sections of many northern structures, such as
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago, although the exact origin and timing of the evolution of dinosaurs is the subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Reverse genetic engineering and the fossil record both demonstrate that birds are modern feathered dinosaurs, having evolved from earlier theropods during the late Jurassic Period; as such, birds were the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event 66 million years ago. Dinosaurs can therefore be divided into birds; this article deals with non-avian dinosaurs. Dinosaurs are a varied group of animals from taxonomic and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish. Using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs.
Dinosaurs are represented on every continent by fossil remains. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded. Most research conducted since the 1970s, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction; some were herbivorous, others carnivorous. Evidence suggests that egg-laying and nest-building are additional traits shared by all dinosaurs and non-avian alike. While dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, some extinct groups developed skeletal modifications such as bony armor and spines. While the dinosaurs' modern-day surviving avian lineage are small due to the constraints of flight, many prehistoric dinosaurs were large-bodied—the largest sauropod dinosaurs are estimated to have reached lengths of 39.7 meters and heights of 18 meters and were the largest land animals of all time.
Still, the idea that non-avian dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large, sturdy bones are more to last until they are fossilized. Many dinosaurs were quite small: Xixianykus, for example, was only about 50 cm long. Since the first dinosaur fossils were recognized in the early 19th century, mounted fossil dinosaur skeletons have been major attractions at museums around the world, dinosaurs have become an enduring part of world culture; the large sizes of some dinosaur groups, as well as their monstrous and fantastic nature, have ensured dinosaurs' regular appearance in best-selling books and films, such as Jurassic Park. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, new discoveries are covered by the media; the taxon'Dinosauria' was formally named in 1841 by paleontologist Sir Richard Owen, who used it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were being recognized in England and around the world.
The term is derived from Ancient Greek δεινός, meaning'terrible, potent or fearfully great', σαῦρος, meaning'lizard or reptile'. Though the taxonomic name has been interpreted as a reference to dinosaurs' teeth and other fearsome characteristics, Owen intended it to evoke their size and majesty. Other prehistoric animals, including pterosaurs, ichthyosaurs and Dimetrodon, while popularly conceived of as dinosaurs, are not taxonomically classified as dinosaurs. Pterosaurs are distantly related to dinosaurs; the other groups mentioned are, like dinosaurs and pterosaurs, members of Sauropsida, except Dimetrodon. Under phylogenetic nomenclature, dinosaurs are defined as the group consisting of the most recent common ancestor of Triceratops and Neornithes, all its descendants, it has been suggested that Dinosauria be defined with respect to the MRCA of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria. Both definitions result in the same set of animals being defined as dinosaurs: "Dinosauria = Ornithischia + Saurischia", encompassing ankylosaurians, ceratopsians, ornithopods and sauropodomorphs.
Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a separate class that had evolved from dinosaurs, a distinct superorder. However, a majority of contemporary paleontologists concerned with dinosaurs reject the traditional style of classification in favor of phylogenetic taxonomy. Birds are thus considered to be dinosaurs and dinosaurs are, not extinct. Birds are classified as belonging to the subgroup M
The flowering plants known as angiosperms, Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families 13,164 known genera and c. 369,000 known species. Like gymnosperms, angiosperms are seed-producing plants. However, they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, the production of fruits that contain the seeds. Etymologically, angiosperm means a plant; the term comes from the Greek words sperma. The ancestors of flowering plants diverged from gymnosperms in the Triassic Period, 245 to 202 million years ago, the first flowering plants are known from 160 mya, they diversified extensively during the Early Cretaceous, became widespread by 120 mya, replaced conifers as the dominant trees from 100 to 60 mya. Angiosperms differ from other seed plants in several ways, described in the table below; these distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans.
Angiosperm stems are made up of seven layers. The amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms; the vascular bundles of the stem are arranged such that the phloem form concentric rings. In the dicotyledons, the bundles in the young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles, a complete ring is formed, a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside; the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.
Among the monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They once formed the stem increases in diameter only in exceptional cases; the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, provide the most trustworthy external characteristics for establishing relationships among angiosperm species; the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally from the axil of a leaf; as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More the flower-bearing portion of the plant is distinguished from the foliage-bearing or vegetative portion, forms a more or less elaborate branch-system called an inflorescence. There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become pollen grains, are the "male" cells and are borne in the stamens.
The "female" cells called megaspores, which will divide to become the egg cell, are contained in the ovule and enclosed in the carpel. The flower may consist only of these parts, as in willow, where each flower comprises only a few stamens or two carpels. Other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators; the individual members of these surrounding structures are known as petals. The outer series is green and leaf-like, functions to protect the rest of the flower the bud; the inner series is, in general, white or brightly colored, is more delicate in structure. It functions to attract bird pollinators. Attraction is effected by color and nectar, which may be secreted in some part of the flower; the characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans. While the majority of flowers are perfect or hermaphrodite, flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization.
Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot transfer pollen to the pistil. Homomorphic flowers may employ a biochemical mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers; the botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon and σπέρμα, was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked; the term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any