In cladistics, a monophyletic group, or clade, is a group of organisms that consists of all the descendants of a common ancestor. Monophyletic groups are characterised by shared derived characteristics, which distinguish organisms in the clade from other organisms; the arrangement of the members of a monophyletic group is called a monophyly. Monophyly is contrasted with polyphyly as shown in the second diagram. A paraphyletic group consists of all of the descendants of a common ancestor minus one or more monophyletic groups. A polyphyletic group is characterized by convergent habits of scientific interest; the features by which a polyphyletic group is differentiated from others are not inherited from a common ancestor. These definitions have taken some time to be accepted; when the cladistics school of thought became mainstream in the 1960s, several alternative definitions were in use. Indeed, taxonomists sometimes used terms without defining them, leading to confusion in the early literature, a confusion which persists.
The first diagram shows a phylogenetic tree with two monophyletic groups. The several groups and subgroups are situated as branches of the tree to indicate ordered lineal relationships between all the organisms shown. Further, any group may be considered a taxon by modern systematics, depending upon the selection of its members in relation to their common ancestor; the term monophyly, or monophyletic, derives from the two Ancient Greek words μόνος, meaning "alone, unique", φῦλον, meaning "genus, species", refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor. Conversely, the term polyphyly, or polyphyletic, builds on the ancient greek prefix πολύς, meaning "many, a lot of", refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources. By comparison, the term paraphyly, or paraphyletic, uses the ancient greek prefix παρά, meaning "beside, near", refers to the situation in which one or several monophyletic subgroups are left apart from all other descendants of a unique common ancestor.
That is, a paraphyletic group is nearly monophyletic, hence the prefix pará. On the broadest scale, definitions fall into two groups. Willi Hennig defined monophyly as groups based on synapomorphy; some authors have sought to define monophyly to include paraphyly as any two or more groups sharing a common ancestor. However, this broader definition encompasses both monophyletic and paraphyletic groups as defined above. Therefore, most scientists today restrict the term "monophyletic" to refer to groups consisting of all the descendants of one common ancestor. However, when considering taxonomic groups such as genera and species, the most appropriate nature of their common ancestor is unclear. Assuming that it would be one individual or mating pair is unrealistic for sexually reproducing species, which are by definition interbreeding populations. Monophyly and associated terms are restricted to discussions of taxa, are not accurate when used to describe what Hennig called tokogenetic relationships—now referred to as genealogies.
Some argue that using a broader definition, such as a species and all its descendants, does not work to define a genus. The loose definition fails to recognize the relations of all organisms. According to D. M. Stamos, a satisfactory cladistic definition of a species or genus is impossible because many species may form by "budding" from an existing species, leaving the parent species paraphyletic. Clade Crown group Glossary of scientific naming Monotypic taxon Paraphyly Polyphyly Abbey, Darren. "Graphical explanation of basic phylogenetic terms". University of California, Berkeley. Retrieved 15 January 2010. Carr, Steven M.. "Concepts of monophyly, polyphyly & paraphyly". Memorial University. Retrieved 15 January 2010. Hyvönen, Jaako. "Monophyly, compromise". University of Helsinki. Retrieved 15 January 2010
Jeffersonia, known as twinleaf or rheumatism root, is a small genus of herbaceous perennial plants in the family Berberidaceae. They are uncommon spring grow in limestone soils of rich deciduous forests. Jeffersonia was named for United States President Thomas Jefferson by his contemporary Benjamin Smith Barton; this genus was grouped in genus Podophyllum. Twinleaf is protected by state laws as a threatened or endangered plant in Georgia, New York, New Jersey; the leaves and flowers of this plant are smooth and emerge directly from the rhizome at base of the plant. Jeffersonia has showy white flowers with eight petals; the short-lived flower appears in May, before the forest canopy appears. The fruit is a green pear-shaped capsule with a hinged top; the characteristic leaves are large and nearly divided in half, giving rise to its common name, twinleaf. Plants in this genus grow taller than 12 inches; as with many other deciduous forest plants, the seeds are dispersed by ants, a process known as myrmecochory.
Accepted speciesJeffersonia diphylla Pers. – Eastern North America Great Lakes region, Ohio Valley, Appalachiansunresolved namesJeffersonia dubia Benth. & Hook. f. ex Baker & Moore – China, Russia Jeffersonia lobata Nutt. Jeffersonia odorata Raf.species in homonymic genusIn 1800, Brickell used the name Jeffersonia to refer to some plants in the Loganiaceae, thus creating an illegitimate homonym. Species names coined using this illegitimate use of the name: Jeffersonia sempervirens Brickell, now called Gelsemium sempervirens J. St.-Hil Jeffersonia has had a variety of medical uses. One is hinted at by an archaic common name of Jeffersonia diphylla, Rheumatism root; the roots of both species contain berberine, a known anti-tumor alkaloid. The plant is therefore considered poisonous. Native Americans use Jeffersonia diphylla for a variety of medicines; the Cherokee use an infusion of this plant for treating dropsy, as well as gravel and urinary tract problems, as a poultice for sores and inflammation.
The Iroquois used a decoction of the plant to treat diarrhea. The whole plant was used in early American medicine as an antispasmodic, emetic and general tonic; the "root" was once used as an emetic in large doses, as an expectorant in small doses. Modern medicine does not use this plant. Traditional Chinese medicine uses Jeffersonia dubia for strengthening the stomach and bringing down fevers
Cephalon (arthropod head)
The cephalon is the head section of an arthropod. It is a tagma; the word cephalon derives from the Greek κεφαλή, meaning "head". In insects, head is a preferred term. In chelicerates and crustaceans, the cephalothorax is derived from the fusion of the cephalon and the thorax, is covered by a single unsegmented carapace. In relation with the arthropod head problem, phylogeny studies show that members of the Malacostraca class of crustaceans have five segments in the cephalon, when not fused with the thorax to form a cephalothorax. In the Late Precambrian or Lower Cambrian Proarticulata species Praecambridium sigillum, that superficially resembles a trilobite, the term is used to describe the anterior part of the animal; the head of the Thylacocephala is referred to as a cephalon. Thylacocephala are a unique group of extinct arthropods, with possible crustacean affinities, thought to occur from the lower Cambrian, but with certainty between the Lower Silurian and the Upper Cretaceous; the cephalon of trilobites is variable with a lot of morphological complexity.
The glabella, the expression of the axial lobe in the cephalon, forms a dome underneath which sat the "crop" or "stomach". The exoskeleton has few distinguishing ventral features, but the cephalon preserves muscle attachment scars and the hypostome, a small rigid plate comparable to the ventral plate in other arthropods. A toothless mouth and stomach sat upon the hypostome with the mouth facing backwards at the rear edge of the hypostome. Hypostome morphology is variable. Many variations in shape and placement of the hypostome have been described; the size of the glabella and the lateral fringe of the cephalon, together with hypostome variation, have been linked to different lifestyles and specific ecological niches. The lateral fringe of the cephalon is exaggerated in the Harpetida, in other species a bulge in the pre-glabellar area is preserved that suggests a brood pouch. Complex compound eyes are another obvious feature of the cephalon; when trilobites moulted, the librigenae separated along the facial suture to assist moulting, leaving the cranidium exposed.
Trilobite facial sutures can be divided into three main types according to where the sutures end relative to the genal angle. Early Cambrian trilobites belonging to the suborder. Other trilobites lost facial sutures secondarily. Carapace Facial suture Pygidium Tagma Thorax
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
Cyphaspis is a genus of small trilobite that lived from the Late Ordovician to the Late Devonian. Fossils have been found in marine strata in what is now Europe and North America. Various species had a compact body, a large, bulbous glabellum. Many species had long spines arranged to related genera, such as Otarian, Otarionella and Namuropyge; the following species in the genus Cyphaspis have been described: Fossils of Cyphaspis have been found in: DevonianColombia, the Czech Republic, United States, Uzbekistan SilurianCanada, the United Kingdom, the United States OrdovicianSweden, the United States Richard Fortey, Trilobite: Eyewitness to Evolution Cyphasis on Trilobites.info
Permian–Triassic extinction event
The Permian–Triassic extinction event, colloquially known as the Great Dying, the End-Permian Extinction or the Great Permian Extinction, occurred about 252 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as between the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct, it was the largest known mass extinction of insects. Some 57% of all biological families and 83% of all genera became extinct; because so much biodiversity was lost, the recovery of land-dwelling life took longer than after any other extinction event up to 10 million years. Studies in Bear Lake County, near Paris, showed a quick rebound in a localized marine ecosystem, taking around 2 million years to recover, suggesting that the impact of the extinction may have been felt less in some areas than others. There is evidence for phases, of extinction. Suggested mechanisms for the latter include one or more large meteor impact events, massive volcanism such as that of the Siberian Traps, the ensuing coal or gas fires and explosions, a runaway greenhouse effect triggered by sudden release of methane from the sea floor due to methane clathrate dissociation according to the clathrate gun hypothesis or methane-producing microbes known as methanogens.
Possible contributing gradual changes include sea-level change, increasing anoxia, increasing aridity, a shift in ocean circulation driven by climate change. Until 2000, it was thought that rock sequences spanning the Permian–Triassic boundary were too few and contained too many gaps for scientists to reliably determine its details. However, it is now possible to date the extinction with millennial precision. U–Pb zircon dates from five volcanic ash beds from the Global Stratotype Section and Point for the Permian–Triassic boundary at Meishan, establish a high-resolution age model for the extinction – allowing exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, recovery at millennial timescales; the extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Ma ago, a duration of 60 ± 48 ka. A large, abrupt global decrease in the ratio of the stable isotope 13C to that of 12C, coincides with this extinction, is sometimes used to identify the Permian–Triassic boundary in rocks that are unsuitable for radiometric dating.
Further evidence for environmental change around the P–Tr boundary suggests an 8 °C rise in temperature, an increase in CO2 levels by 2000 ppm. There is evidence of increased ultraviolet radiation reaching the earth, causing the mutation of plant spores, it has been suggested that the Permian–Triassic boundary is associated with a sharp increase in the abundance of marine and terrestrial fungi, caused by the sharp increase in the amount of dead plants and animals fed upon by the fungi. For a while this "fungal spike" was used by some paleontologists to identify the Permian–Triassic boundary in rocks that are unsuitable for radiometric dating or lack suitable index fossils, but the proposers of the fungal spike hypothesis pointed out that "fungal spikes" may have been a repeating phenomenon created by the post-extinction ecosystem in the earliest Triassic; the idea of a fungal spike has been criticized on several grounds, including: Reduviasporonites, the most common supposed fungal spore, may be a fossilized alga.
The reduviasporonites may represent a transition to a lake-dominated Triassic world rather than an earliest Triassic zone of death and decay in some terrestrial fossil beds. Newer chemical evidence agrees better with a fungal origin for Reduviasporonites, diluting these critiques. Uncertainty exists regarding the duration of the overall extinction and about the timing and duration of various groups' extinctions within the greater process; some evidence suggests that there were multiple extinction pulses or that the extinction was spread out over a few million years, with a sharp peak in the last million years of the Permian. Statistical analyses of some fossiliferous strata in Meishan, Zhejiang Province in southeastern China, suggest that the main extinction was clustered around one peak. Recent research shows. In a well-preserved sequence in east Greenland, the decline of animals is concentrated in a period 10,000 to 60,000 years long, with plants taking an additional several hundred thousand years to show the full impact of the event.
An older theory, still supported in some recent papers, is that there were two major extinction pulses 9.4 million years apart, separated by a period of extinctions well above the background level, that the final extinction killed off only about 80% of marine species alive at that time while the other losses occurred during the first pulse or the interval between pulses. According to this theory one of these extinction pulses occurred at the end of the Guadalupian epoch of the Permian. For example, all but one of the surviving dinocephalian genera died out at the end of the Guadalupian, as did the Verbeekinidae, a family of large-size fusuline foraminifera; the impact of the end-Guadalupian extinction on marine organisms appears to have varied between locations and between taxonomi
The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, the longest period of the Phanerozoic Eon; the Cretaceous Period is abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas; these oceans and seas were populated with now-extinct marine reptiles and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared; the Cretaceous ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.
The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk, found in the upper Cretaceous of Western Europe. The name Cretaceous was derived from Latin creta; the Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series. In older literature the Cretaceous is sometimes divided into three series: Neocomian and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use; as with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is defined, being placed at an iridium-rich layer found worldwide, believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and into the Gulf of Mexico.
This layer has been dated at 66.043 Ma. A 140 Ma age for the Jurassic-Cretaceous boundary instead of the accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences. From youngest to oldest, the subdivisions of the Cretaceous period are: Late Cretaceous Maastrichtian – Campanian – Santonian – Coniacian – Turonian – Cenomanian – Early Cretaceous Albian – Aptian – Barremian – Hauterivian – Valanginian – Berriasian – The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms; the Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type, formed under warm, shallow marine circumstances.
Due to the high sea level, there was extensive space for such sedimentation. Because of the young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for the Cretaceous, it consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas. In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast; the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not consolidated and the Chalk Group still consists of loose sediments in many places; the group has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is a marine system consisting of competent limestone beds or incompetent marls.
Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval; these shales are an important source rock for oil and gas, for example in the subsurface of the North Sea. During th