The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and with the end of the Paleolithic age used in archaeology; the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Middle Pleistocene and Upper Pleistocene. In addition to this international subdivision, various regional subdivisions are used. Before a change confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present, as opposed to the accepted 2.588 million years BP: publications from the preceding years may use either definition of the period. Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.
This distinguished it from the older Pliocene epoch, which Lyell had thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek πλεῖστος, pleīstos, "most", καινός, kainós, "new"; the Pleistocene has been dated from 2.588 million to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell; the end of the Younger Dryas has been dated to about 9640 BC. The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not different from previous interglacial intervals within the Pleistocene, it was not until after the development of radiocarbon dating, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites. In 2009 the International Union of Geological Sciences confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.
The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W; the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus; the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age; the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were at their present positions during the Pleistocene, the plates upon which they sit having moved no more than 100 km relative to each other since the beginning of the period.
According to Mark Lynas, the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places, it is estimated. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, several hundred in Eurasia; the mean annual temperature at the edge of the ice was −6 °C. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres thick, resulting in temporary sea-level drops of 100 metres or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the current decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one; the Cordilleran ice sheet covered the North American northwest. The Fenno-Scandian ice sheet rested including much of Great Britain. Scattered domes stretched across Siberi
California is a state in the Pacific Region of the United States. With 39.6 million residents, California is the most populous U. S. the third-largest by area. The state capital is Sacramento; the Greater Los Angeles Area and the San Francisco Bay Area are the nation's second and fifth most populous urban regions, with 18.7 million and 9.7 million residents respectively. Los Angeles is California's most populous city, the country's second most populous, after New York City. California has the nation's most populous county, Los Angeles County, its largest county by area, San Bernardino County; the City and County of San Francisco is both the country's second-most densely populated major city after New York City and the fifth-most densely populated county, behind only four of the five New York City boroughs. California's $3.0 trillion economy is larger than that of any other state, larger than those of Texas and Florida combined, the largest sub-national economy in the world. If it were a country, California would be the 5th largest economy in the world, the 36th most populous as of 2017.
The Greater Los Angeles Area and the San Francisco Bay Area are the nation's second- and third-largest urban economies, after the New York metropolitan area. The San Francisco Bay Area PSA had the nation's highest GDP per capita in 2017 among large PSAs, is home to three of the world's ten largest companies by market capitalization and four of the world's ten richest people. California is considered a global trendsetter in popular culture, innovation and politics, it is considered the origin of the American film industry, the hippie counterculture, fast food, the Internet, the personal computer, among others. The San Francisco Bay Area and the Greater Los Angeles Area are seen as global centers of the technology and entertainment industries, respectively. California has a diverse economy: 58% of the state's economy is centered on finance, real estate services and professional, scientific and technical business services. Although it accounts for only 1.5% of the state's economy, California's agriculture industry has the highest output of any U.
S. state. California is bordered by Oregon to the north and Arizona to the east, the Mexican state of Baja California to the south; the state's diverse geography ranges from the Pacific Coast in the west to the Sierra Nevada mountain range in the east, from the redwood–Douglas fir forests in the northwest to the Mojave Desert in the southeast. The Central Valley, a major agricultural area, dominates the state's center. Although California is well-known for its warm Mediterranean climate, the large size of the state results in climates that vary from moist temperate rainforest in the north to arid desert in the interior, as well as snowy alpine in the mountains. Over time and wildfires have become more pervasive features. What is now California was first settled by various Native Californian tribes before being explored by a number of European expeditions during the 16th and 17th centuries; the Spanish Empire claimed it as part of Alta California in their New Spain colony. The area became a part of Mexico in 1821 following its successful war for independence but was ceded to the United States in 1848 after the Mexican–American War.
The western portion of Alta California was organized and admitted as the 31st state on September 9, 1850. The California Gold Rush starting in 1848 led to dramatic social and demographic changes, with large-scale emigration from the east and abroad with an accompanying economic boom; the word California referred to the Baja California Peninsula of Mexico. The name derived from the mythical island California in the fictional story of Queen Calafia, as recorded in a 1510 work The Adventures of Esplandián by Garci Rodríguez de Montalvo; this work was the fifth in a popular Spanish chivalric romance series that began with Amadis de Gaula. Queen Calafia's kingdom was said to be a remote land rich in gold and pearls, inhabited by beautiful black women who wore gold armor and lived like Amazons, as well as griffins and other strange beasts. In the fictional paradise, the ruler Queen Calafia fought alongside Muslims and her name may have been chosen to echo the title of a Muslim leader, the Caliph. It's possible.
Know ye that at the right hand of the Indies there is an island called California close to that part of the Terrestrial Paradise, inhabited by black women without a single man among them, they lived in the manner of Amazons. They were robust of body with great virtue; the island itself is one of the wildest in the world on account of the craggy rocks. Shortened forms of the state's name include CA, Cal. Calif. and US-CA. Settled by successive waves of arrivals during the last 10,000 years, California was one of the most culturally and linguistically diverse areas in pre-Columbian North America. Various estimates of the native population range from 100,000 to 300,000; the Indigenous peoples of California included more than 70 distinct groups of Native Americans, ranging from large, settled populations living on the coast to groups in the interior. California groups were diverse in their political organization with bands, villages, on the resource-rich coasts, large chiefdoms, such as the Chumash and Salinan.
Trade, intermarriage a
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in fresh water, brackish water, or salt water; the green crab is an example of a euryhaline invertebrate that can live in brackish water. Euryhaline organisms are found in habitats such as estuaries and tide pools where the salinity changes regularly. However, some organisms are euryhaline because their life cycle involves migration between freshwater and marine environments, as is the case with salmon and eels; the opposite of euryhaline organisms are stenohaline ones, which can only survive within a narrow range of salinities. Most freshwater organisms are stenohaline, will die in seawater, most marine organisms are stenohaline, cannot live in fresh water. Osmoregulation is the active process; the osmotic pressure in the body is homeostatically regulated in such a manner that it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another by osmosis.
Two major types of osmoregulation are osmoregulators. Osmoconformers match their body osmolarity to their environment or passively. Most marine invertebrates are osmoconformers, although their ionic composition may be different from that of seawater. Osmoregulators regulate their body osmolarity, which always stays constant, are more common in the animal kingdom. Osmoregulators control salt concentrations despite the salt concentrations in the environment. An example is freshwater fish; the gills uptake salt from the environment by the use of mitochondria-rich cells. Water will diffuse into the fish, so it excretes a hypotonic urine to expel all the excess water. A marine fish has an internal osmotic concentration lower than that of the surrounding seawater, so it tends to lose water and gain salt, it excretes salt out from the gills. Most fish are stenohaline, which means they are restricted to either salt or fresh water and cannot survive in water with a different salt concentration than they are adapted to.
However, some fish show a tremendous ability to osmoregulate across a broad range of salinities. Salmon has been observed to inhabit two utterly disparate environments — marine and fresh water — and it is inherent to adapt to both by bringing in behavioral and physiological modifications; some marine fish, like sharks, have adopted a different, efficient mechanism to conserve water, i.e. osmoregulation. They retain urea in their blood in higher concentration. Urea is damaging to living tissue so, to cope with this problem, some fish retain trimethylamine oxide; this provides a better solution to urea's toxicity. Sharks, having higher solute concentration, do not drink water like marine fish; some euryhaline fish The level of salinity in intertidal zones can be quite variable. Low salinities can be caused by river inputs of freshwater. Estuarine species must be euryhaline, or able to tolerate a wide range of salinities. High salinities occur in locations with high evaporation rates, such as in salt marshes and high intertidal pools.
Shading by plants in the salt marsh, can slow evaporation and thus ameliorate salinity stress. In addition, salt marsh plants tolerate high salinities by several physiological mechanisms, including excreting salt through salt glands and preventing salt uptake into the roots. Despite having a regular freshwater presence, the Atlantic stingray is physiologically euryhaline and no population has evolved the specialized osmoregulatory mechanisms found in the river stingrays of the family Potamotrygonidae; this may be due to the recent date of freshwater colonization, and/or incomplete genetic isolation of the freshwater populations, as they remain capable of surviving in salt water. Freshwater Atlantic stingrays have only 30-50% the concentration of urea and other osmolytes in their blood compared to marine populations. However, the osmotic pressure between their internal fluids and external environment still causes water to diffuse into their bodies, they must produce large quantities of dilute urine to compensate.
Partial list other euryhaline organisms Fish migration Osmoregulation Stenohaline Osmoconformer
Central Valley Project
The Central Valley Project is a federal water management project in the U. S. state of California under the supervision of the United States Bureau of Reclamation. It was devised in 1933 in order to provide irrigation and municipal water to much of California's Central Valley—by regulating and storing water in reservoirs in the northern half of the state, transporting it to the water-poor San Joaquin Valley and its surroundings by means of a series of canals and pump plants, some shared with the California State Water Project. Many CVP water users are represented by the Central Valley Project Water Association. In addition to water storage and regulation, the system has a hydroelectric capacity of over 2,000 megawatts, provides recreation and flood control with its twenty dams and reservoirs, it has allowed major cities to grow along Valley rivers which would flood each spring, transformed the semi-arid desert environment of the San Joaquin Valley into productive farmland. Freshwater stored in Sacramento River reservoirs and released downriver during dry periods prevents salt water from intruding into the Sacramento-San Joaquin Delta during high tide.
There are eight divisions of the project and ten corresponding units, many of which operate in conjunction, while others are independent of the rest of the network. California agriculture and related industries now directly account for 7% of the gross state product for which the CVP supplied water for about half. Many CVP operations have had considerable environmental consequences, including a decline in the salmon population of four major California rivers in the northern state, the reduction of riparian zones and wetlands. Many historical sites and Native American tribal lands have been flooded by CVP reservoirs. In addition, runoff from intensive irrigation has groundwater; the Central Valley Project Improvement Act, passed in 1992, intends to alleviate some of the problems associated with the CVP with programs like the Refuge Water Supply Program. In recent years, a combination of drought and regulatory decisions passed based on the Endangered Species Act of 1973 have forced Reclamation to turn off much of the water for the west side of the San Joaquin Valley in order to protect the fragile ecosystem in the Sacramento-San Joaquin Delta and keep alive the dwindling fish populations of Northern and Central California rivers.
In 2017 the Klamath and Trinity rivers witnessed the worst fall run Chinook salmon return in recorded history, leading to a disaster declaration in California and Oregon due to the loss of the commercial fisheries. The recreational fall Chinook salmon fishery in both the ocean and the Trinity and Klamath rivers was closed in 2017. Only 1,123 adult winter Chinook salmon returned to the Sacramento Valley in 2017, according to a report sent to the Pacific Fishery Management Council by the California Department of Fish and Wildlife; this is the second lowest number of returning adult winter run salmon since modern counting techniques were implemented in 2003. By comparison, over 117,000 winter Chinooks returned to spawn in 1969; the CVP stores about 13 million acre feet of water in 20 reservoirs in the foothills of the Sierra Nevada, the Klamath Mountains and the California Coast Ranges, passes about 7.4 million acre feet of water annually through its canals. Of the water transported, about 5 million acre feet goes to irrigate 3,000,000 acres of farmland, 600,000 acre feet supplies municipal uses, 800,000 acre feet is released into rivers and wetlands in order to comply with state and federal ecological standards.
Two large reservoirs, Shasta Lake and Trinity Lake, are formed by a pair of dams in the mountains north of the Sacramento Valley. Water from Shasta Lake flows into the Sacramento River which flows to the Sacramento-San Joaquin Delta and water from Trinity Lake flows into the Trinity River which leads to the Pacific Ocean. Both lakes release water at controlled rates. There, before it can flow on to San Francisco Bay and the Pacific Ocean, some of the water is intercepted by a diversion channel and transported to the Delta-Mendota Canal, which conveys water southwards through the San Joaquin Valley, supplying water to San Luis Reservoir and the San Joaquin River at Mendota Pool in the process reaching canals that irrigates farms in the valley. Friant Dam crosses the San Joaquin River upstream of Mendota Pool, diverting its water southwards into canals that travel into the Tulare Lake area of the San Joaquin Valley, as far south as the Kern River. New Melones Lake, a separate facility, stores water flow of a San Joaquin River tributary for use during dry periods.
Other smaller, independent facilities exist to provide water to local irrigation districts. Despite the rich soils and favorable weather of the 42,000-square-mile Central Valley, inhabitants of the valley who were unfamiliar with its natural rainfall patterns and started to practice intense irrigated agriculture on the arid land soon found themselves troubled by frequent floods in the Sacramento Valley and a general lack of water in the San Joaquin Valley; the Sacramento River, which drains the northern part, receives between 60–75% of the precipitation in the Valley, despite the Sacramento Valley covering less area than the much larger San Joaquin Valley, drained by the San Joaquin River, which receives only about 25% of the rainfall. Furthermore, cities drawing water from the Sacramento-San Joaquin Delta faced problems in dry summer and autumn months when the inflowing water was low. In order to continue to sustain the valley's
United States Fish and Wildlife Service
The United States Fish and Wildlife Service is an agency of the US Federal Government within the US Department of the Interior dedicated to the management of fish and natural habitats. The mission of the agency is "working with others to conserve and enhance fish, wildlife and their habitats for the continuing benefit of the American people." Aurelia Skipwith is Trump's nominee. Among the responsibilities of the FWS are enforcing federal wildlife laws. Sub-units of the FWS include: National Wildlife Refuge System—560 National Wildlife Refuges and thousands of small wetlands and other special management areas covering over 150 million acres Division of Migratory Bird Management Federal Duck Stamp National Fish Hatchery System—70 National Fish Hatcheries and 65 Fish and Wildlife Conservation Offices Endangered Species program—86 Ecological Services Field Stations International Affairs Program National Conservation Training Center USFWS Office of Law Enforcement Clark R. Bavin National Fish and Wildlife Forensic Laboratory Landscape Conservation CooperativesThe vast majority of fish and wildlife habitat is on non-federal state or private land.
Therefore, the FWS works with private groups such as Partners in Flight and Sport Fishing and Boating Partnership Council to promote voluntary habitat conservation and restoration. The FWS employs 9,000 people and is organized into a central administrative office in Falls Church, eight regional offices, nearly 700 field offices distributed throughout the United States; the FWS originated in 1871 as the United States Commission on Fish and Fisheries, more referred to as the United States Fish Commission, created by the United States Congress with the purpose of studying and recommending solutions to a noted decline in the stocks of food fish. Spencer Fullerton Baird was appointed its first commissioner. In 1903, the Fish Commission was reorganized as the United States Bureau of Fisheries. In 1885–1886, the Division of Economic Ornithology and Mammalogy was established within the United States Department of Agriculture. In 1896 it became the Division of Biological Survey, its early work focused on the effect of birds in controlling agricultural pests and mapping the geographical distribution of plants and animals in the United States.
Clinton Hart Merriam headed the Bureau for 25 years and became a national figure for improving the scientific understanding of birds and mammals in the United States. Jay Norwood Darling was appointed Chief of the new Bureau of Biological Survey in 1934. Under Darling's guidance, the Bureau began an ongoing legacy of protecting vital natural habitat throughout the country; the FWS was created in 1940, when the Bureaus of Fisheries and Biological Survey were combined after being moved to the Department of the Interior. In 1959, the methods used by FWS's Animal Damage Control Program were featured in the Tom Lehrer song "Poisoning Pigeons in the Park"; the FWS governs six US National Monuments: Hanford Reach National Monument in Washington state. Pursuant to the eagle feather law, Title 50, Part 22 of the Code of Federal Regulations, the Bald and Golden Eagle Protection Act, the US Fish and Wildlife Service administers the National Eagle Repository and the permit system for Native American religious use of eagle feathers.
These exceptions only apply to Native Americans that are registered with the federal government and are enrolled with a federally recognized tribe. In the late 1990s and early 2000s, the FWS began to incorporate the research of tribal scientists into conservation decisions; this came on the heels of Native American traditional ecological knowledge gaining acceptance in the scientific community as a reasonable and respectable way to gain knowledge of managing the natural world. Additionally, other natural resource agencies within the United States government, such as the USDA, have taken steps to be more inclusive of tribes, native people, tribal rights; this has marked a transition to a relationship of more co-operation rather than the tension between tribes and government agencies seen historically. Today, these agencies work with tribal governments to ensure the best conservation decisions are made and that tribes retain their sovereignty. Federal law enforcement in the United States Atlantic Coastal Cooperative Statistics Program National Fish and Wildlife Forensics Laboratory National Oceanic and Atmospheric Admini
The largemouth bass is a carnivorous freshwater gamefish in the Centrarchidae family, a species of black bass native to much of the United States And Northern Mexico. It is known by a variety of regional names, such as the widemouth bass, bigmouth bass, black bass, largies, Potter's fish, Florida bass, Florida largemouth, green bass, Green trout, gilsdorf bass, Oswego bass, southern largemouth and northern largemouth, LMB; the largemouth bass is the state fish of Georgia and Indiana, the state freshwater fish of Florida and Alabama, the state sport fish of Tennessee. The largemouth bass is an olive-green to greenish gray fish, marked by a series of dark, sometimes black, blotches forming a jagged horizontal stripe along each flank; the upper jaw of a largemouth bass extends beyond the rear margin of the orbit. In comparison to age, a female bass is larger than a male; the largemouth is the largest of the black basses, reaching a maximum recorded overall length of 29.5 in and a maximum unofficial weight of 25 pounds 1 ounce.
The fish lives 10 to 16 years on average. The juvenile largemouth bass consumes small bait fish, small shrimp, insects. Adults consume smaller fish, snails, frogs, salamanders and small water birds and baby alligators. In larger lakes and reservoirs, adult bass occupy deeper water than younger fish, shift to a diet consisting entirely of smaller fish like shad, yellow perch, ciscoes and sunfish, it consumes younger members of larger fish species, such as catfish, walleye, white bass, striped bass, smaller black bass. Prey items can be larger. Studies of prey utilization by largemouths show that in weedy waters, bass grow more due to difficulty in acquiring prey. Less weed cover allows bass to more find and catch prey, but this consists of more open-water baitfish. With little or no cover, bass can starve or be stunted. Fisheries managers must consider these factors when designing regulations for specific bodies of water. Under overhead cover, such as overhanging banks, brush, or submerged structure, such as weedbeds, humps and drop-offs, the largemouth bass uses its senses of hearing, sight and smell to attack and seize its prey.
Adult largemouth are apex predators within their habitat, but they are preyed upon by many animals while young. Notably in the Great Lakes Region, Micropterus salmoides along with many other species of native fish have been known to prey upon the invasive round goby. Remains of said fish have been found inside the stomachs of largemouth bass consistently; this feeding habit may impact the ecosystem positively, but more research must be conducted to verify this. Note that it is illegal to use Neogobius melanostomus as bait in the Great Lakes Region. Largemouth bass reach sexual maturity and begin spawning when they are about a year old. Spawning takes place in the spring season when the water temperature first holds steady above 60˚F. In the northern region of the United States, this occurs anywhere from late April until early July. In the southern states, where the largest and healthiest specimens inhabit, this process can begin in March and is over by June. Males create nests by moving debris from the bottom of the body of water using their tails.
These nests are about twice the length of the males, although this can vary. Bass prefer sand, muck, or gravel bottoms, but will use rocky and weedy bottoms where there is cover for their nest, such as roots or twigs. After finishing the nest, the males swim near the nest looking for a female to mate with. After one is found, the two bass swim around the nest together, turning their bodies so that the eggs and sperm that are being released will come in contact on the way down to the nest. Bass will spawn twice per spring, with some spawning three or four times, although this is not as common; the male will guard the nest until the eggs hatch, which can take about 2 to 4 days in the southern U. S and Northern Mexico, longer in the northern part of its Native Range. Depending on the water temperature, the male will stay with the nest until the infant bass are ready to swim out on their own, which can be about two more weeks after they hatch. After this, the male and newborns will switch to more of a summer mode, in which they focus more on feeding.
Largemouth bass are keenly sought after by anglers and are noted for the excitement of their'fight,' meaning how vigorously the fish resists being hauled into the boat or onto shore after being hooked. The fish will become airborne in their effort to throw the hook, but many say that their cousin species, the smallmouth bass, is more aggressive. Anglers most fish for largemouth bass with lures such as plastic worms, jigs and live bait, such as worms and minnows. A recent trend is the use of large swimbaits to target trophy bass that forage on juvenile rainbow trout in California. Fly fishing for largemouth bass may be done using both topwater and worm imitations tied with natural or synthetic materials. Other Live baits, such as frogs or crawfish, can be productive. In fact, large golden shiners are a popular live bait used to catch trophy bass when they are sluggish in the heat of summer or in the cold of winter. Largemouth bass hang around big patches of weeds and other shallow water cover.
These fish are capable of surviving in a wide variety of climates and waters
A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma