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
Anza-Borrego Desert State Park
Anza-Borrego Desert State Park is a California state park located within the Colorado Desert of southern California, United States. The park takes its name from 18th century Spanish explorer Juan Bautista de Anza and borrego, the Spanish word for sheep. With 600,000 acres that includes one-fifth of San Diego County, it is the largest state park in California; the park occupies eastern San Diego County and reaches into Imperial and Riverside counties, enveloping two communities: Borrego Springs, home to the park's headquarters, Shelter Valley. The park is an anchor in the Mojave and Colorado Deserts Biosphere Reserve, adjacent to the Santa Rosa and San Jacinto Mountains National Monument; the great bowl of the surrounding desert is surrounded by mountains, with the Vallecito Mountains to the south and the highest Santa Rosa Mountains to the north which are in the wilderness area, without paved roads and with the only year-round creeks. The park has 500 mi of dirt roads, 12 designated wilderness areas, 110 mi of hiking trails.
ABDSP is around a two-hour drive northeast from San Diego, southeast from Riverside or Irvine, south from Palm Springs. Access on the east-Coachella Valley side is via County Route S22 and State Route 78. Access on the west-Pacific Ocean side is via California County Routes S79. S67 provides access through the high and forested Laguna Mountains, such as in Cuyamaca Rancho State Park; these highways climb from the coast to 2,400 ft above sea level descend 2,000 ft down into the Borrego Valley in the center of the park. Park information and maps are available in the Visitor Center; the park has Wi-Fi access. The habitats are within the Colorado Desert ecosystem of the Sonoran Desert ecoregion; the higher extreme northern and eastern sections in the Peninsular Ranges are in the California montane chaparral and woodlands ecoregion. The park contains bajadas and desert washes; the bajadas are predominantly creosote bush-bur sage with creosote bush and the palo verde-cactus shrub ecosystems with the palo verde tree and ocotillo.
In the washes, Colorado/Sonoran microphylla woodlands can be found. These woodlands include such plants as smoke tree, velvet mesquite, catclaw; the park has natural oases, with the state's only native palm, the California Fan Palm. Seasonal wildflower displays can be seen in many plant community association throughout the park; the high-country to the north and east has closed-cone pine forests and oak woodlands. The oases are prolific with many types of fauna for bird-watching. Throughout the park, visitors may see bighorn sheep, mountain lions, kit foxes, mule deer, greater roadrunners, golden eagles, black-tailed jackrabbits, ground squirrels, kangaroo rats and prairie falcons. In the reptile class, desert iguanas and the red diamond rattlesnakes can be seen; some areas are habitats for the Peninsular bighorn sheep called desert bighorn sheep. Few park visitors see them, the sheep avoid human contact. Observers count this endangered species to study the population, monitor its current decline from human encroachment.
The expanses of ABDSP's eroded badlands provide a different view into the region's long-vanished tropical past. The inland of southeastern California was not always a desert. Paleontology, the study of the fossilized remains of ancient life, is the key to understanding this prehistoric world. ABDSP has an exceptional fossil record which includes preserved plants, a variety of invertebrate shells, animal tracks, an array of bones and teeth. Most fossils found in ABDSP date from six million to under a half million years in age, or about 60 million years after the last dinosaur age ended. ABDSP lies in a unique geologic setting along the western margin of the Salton Trough; this major topographic depression with the Salton Sink having elevations of 200 ft below sea level, forms the northernmost end of an active rift valley and a geological continental plate boundary. The trough extends north from the Gulf of California to San Gorgonio Pass, from the eastern rim of the Peninsular Ranges eastward to the San Andreas Fault zone along the far side of the Coachella Valley.
Over the past seven million years, a complete geologic record of over 20,000 ft of fossil-bearing sediment has been deposited within the park along the rift valley's western margin. Paleontological remains are widespread and diverse, are found scattered over hundreds of square miles of eroded badlands terrain extending south from the Santa Rosa Mountains into northern Baja California in Mexico. Both marine and terrestrial environments are represented by this rich fossil record. Six million years ago, the ancestral Gulf of California filled the Salton Trough, extending northward past what would become the city of Palm Springs; these tropical waters supported a profusion of both small marine organisms. Through time, the sea gave way as an immense volume of sediment eroded during the formation of the Grand Canyon spilled into the Salton Trough. Little by little, the ancestral Colorado River built a massive river delta across the sea way. Fossil hardwoods from the deltaic sands and associated coastal plain deposits suggest the region received three times as much rainfall as now.
The Anza-Borrego region changed from a predominately marine environment into a system of interrelated terrestrial habitats. North of the Colorado River Delta and intermittently fed by the river, a
The Sonoran Desert is a North American desert which covers large parts of the Southwestern United States in Arizona and California and of Northwestern Mexico in Sonora, Baja California, Baja California Sur. It is the hottest desert in Mexico, it has an area of 260,000 square kilometers. The western portion of the United States–Mexico border passes through the Sonoran Desert. In phytogeography, the Sonoran Desert is within the Sonoran Floristic Province of the Madrean Region in southwestern North America, part of the Holarctic Kingdom of the northern Western Hemisphere; the desert contains a variety of unique and endemic plants and animals, such as the saguaro and organ pipe cactus. The Sonoran desert wraps around the northern end of the Gulf of California, from Baja California Sur, north through much of Baja California, excluding the central northwest mountains and Pacific west coast, through southeastern California and southwestern and southern Arizona to western and central parts of Sonora.
It is bounded on the west by the Peninsular Ranges, which separate it from the California chaparral and woodlands and Baja California Desert ecoregions of the Pacific slope. To the north in California and northwest Arizona, the Sonoran Desert transitions to the colder-winter, higher-elevation Mojave, Great Basin, Colorado Plateau deserts. To the east and southeast, the deserts transition to the coniferous Arizona Mountains forests and Sierra Madre and Sierra Madre Occidental pine–oak forests at higher elevations. To the south the Sonoran–Sinaloan transition subtropical dry forest is the transition zone from the Sonoran Desert to the tropical dry forests of the Mexican state of Sinaloa; the desert's sub-regions include the Colorado Desert of southeastern California. In the 1957 publication Vegetation of the Sonoran Desert, Forrest Shreve divided the Sonoran Desert into seven regions according to characteristic vegetation: Lower Colorado Valley, Arizona Upland, Plains of Sonora, Foothills of Sonora, Central Gulf Coast, Vizcaíno Region, Magdalena Region.
Many ecologists now consider Shreve's Vizcaíno and Magdalena regions, which lie on the western side of the Baja California Peninsula, to be a separate ecoregion, the Baja California Desert. Within the southern Sonoran Desert in Mexico is found the Gran Desierto de Altar, with the Reserva de la Biosfera el Pinacate y Gran Desierto de Altar, extending 2,000 square kilometers of desert and mountainous regions; the Pinacate National Park includes the only active erg dune region in North America. The nearest city to the Reserva de la Biosfera el Pinacate y Gran Desierto de Altar is Puerto Peñasco in the state of Sonora, Mexico. Sub-regionsSonoran Desert sub-regions include: Colorado Desert Gran Desierto de Altar Lechuguilla Desert Tonopah Desert Yuha Desert Yuma Desert The Sonoran Desert includes 60 mammal species, 350 bird species, 20 amphibian species, over 100 reptile species, 30 native fish species, over 1000 native bee species, more than 2,000 native plant species; the Sonoran Desert area southeast of Tucson and near the Mexican border is vital habitat for the only population of jaguars living within the United States.
The Colorado River Delta was once an ecological hotspot within the Sonoran desert, fueled by the flow of fresh water through the Colorado river in this otherwise dry area, but the delta has been reduced in extent due to the damming and use of the river upstream. Many plants not only thrive in the harsh conditions of the Sonoran Desert. Many have evolved to have specialized adaptations to the desert climate; the Sonoran Desert's biseasonal rainfall pattern results in more plant species than any other desert in the world. The Sonoran Desert includes plant genera and species from the agave family, palm family, cactus family, legume family, numerous others; the Sonoran is the only place in the world. Cholla, hedgehog, prickly pear, nightblooming cereus, organ pipe are other taxa of cacti found here. Cactus provides food and homes to many desert mammals and birds, with showy flowers in reds, pinks and whites, blooming most from late March through June, depending on the species and seasonal temperatures.
Creosote bush and bur sage dominate valley floors. Indigo bush and Mormon tea are other shrubs. Wildflowers of the Sonoran Desert include desert sand verbena, desert sunflower, evening primroses. Ascending from the valley up bajadas, various subtrees such as velvet mesquite, palo verde, desert ironwood, desert willow, crucifixion thorn are common, as well as multi-stemmed ocotillo. Shrubs found at higher elevations include whitethorn acacia, fairy duster, jojoba. In the desert subdivisions found on Baja California, cardon cactus, elephant tree, boojum tree occur; the California fan palm is found in the Colorado Desert section of the Sonoran Desert, the only native palm in California, among many other introduced Arecac
An endangered species is a species, categorized as likely to become extinct. Endangered, as categorized by the International Union for Conservation of Nature Red List, is the second most severe conservation status for wild populations in the IUCN's schema after Critically Endangered. In 2012, the IUCN Red List featured 3,079 animal and 2,655 plant species as endangered worldwide; the figures for 1998 were 1,102 and 1,197. Many nations have laws that protect conservation-reliant species: for example, forbidding hunting, restricting land development or creating preserves. Population numbers and species' conservation status can be found at the lists of organisms by population; the conservation status of a species indicates the likelihood. Many factors are considered; the IUCN Red List of Threatened Species is the best-known worldwide conservation status listing and ranking system. Over 50% of the world's species are estimated to be at risk of extinction. Internationally, 199 countries have signed an accord to create Biodiversity Action Plans that will protect endangered and other threatened species.
In the United States, such plans are called Species Recovery Plans. Though labelled a list, the IUCN Red List is a system of assessing the global conservation status of species that includes "Data Deficient" species – species for which more data and assessment is required before their status may be determined – as well species comprehensively assessed by the IUCN's species assessment process; those species of "Near Threatened" and "Least Concern" status have been assessed and found to have robust and healthy populations, though these may be in decline. Unlike their more general use elsewhere, the List uses the terms "endangered species" and "threatened species" with particular meanings: "Endangered" species lie between "Vulnerable" and "Critically Endangered" species, while "Threatened" species are those species determined to be Vulnerable, Endangered or Critically Endangered; the IUCN categories, with examples of animals classified by them, include: Extinct no remaining individuals of the species Extinct in the wild Captive individuals survive, but there is no free-living, natural population.
Critically endangered Faces an high risk of extinction in the immediate future. Endangered Faces a high risk of extinction in the near future. Vulnerable Faces a high risk of endangerment in the medium term. Near-threatened May be considered threatened in the near future. Least concern No immediate threat to species' survival. A) Reduction in population size based on any of the following: An observed, inferred or suspected population size reduction of ≥ 70% over the last 10 years or three generations, whichever is the longer, where the causes of the reduction are reversible AND understood AND ceased, based on any of the following: direct observation an index of abundance appropriate for the taxon a decline in area of occupancy, extent of occurrence or quality of habitat actual or potential levels of exploitation the effects of introduced taxa, pathogens, competitors or parasites. An observed, inferred or suspected population size reduction of ≥ 50% over the last 10 years or three generations, whichever is the longer, where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on any of to under A1.
A population size reduction of ≥ 50%, projected or suspected to be met within the next 10 years or three generations, whichever is the longer, based on any of to under A1. An observed, inferred, projected or suspected population size reduction of ≥ 50% over any 10 year or three generation period, whichever is longer, where the time period must include both the past and the future, where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on any of to under A1. B) Geographic range in the form of either B1 OR B2 OR both: Extent of occurrence estimated to be less than 5,000 km², estimates indicating at least two of a-c: Severely fragmented or known to exist at no more than five locations. Continuing decline, observed or projected, in any of the following: extent of occurrence area of occupancy area, extent or quality of habitat number of locations or subpopulations number of mature individuals Extreme fluctuations in any of the following: extent of occurrence area of occupancy number of locations or subpopulations number of mature individuals Area of occupancy estimated to be less than 500 km², estimates indicating at least two of a-c: Severely fragmented or known to exist at no more than five locations.
Continuing decline, observed or projected, in any of the following: extent of occurrence area of occupancy area, extent or quality of habitat number of locations or subpopulations number of mature individuals Extreme fluctuations in any of the following: extent of occurrence area of occupancy number of locations or subpopulations number of mature individualsC) Population estimated to number fewer than 2,500 mature individuals and either: An estimated continuing decline of at least 20% within five years or two generations, whichever is longer, OR A continuing decline, projected
Kofa National Wildlife Refuge
The Kofa National Wildlife Refuge is located in Arizona in the southwestern United States, northeast of Yuma and southeast of Quartzsite. The refuge, established in 1939 to protect desert bighorn sheep, encompasses over 665,400 acres of the Yuma Desert region of the Sonoran Desert. Broad sloping foothills as well as the sharp, needlepoint peaks of the Kofa Mountains are found in the rugged refuge; the small scattered waterholes attract a surprising number of water birds for a desert area. A wide variety of plant life is found throughout the refuge; the name Kofa comes from a former area gold mine: the King of Arizona mine, with Kofa a contraction of the name. In 1936, the Arizona Boy Scouts mounted a statewide campaign to save the bighorn sheep, leading to the creation of Kofa; the Scouts first became interested in the sheep through the efforts of Major Frederick Russell Burnham, the noted frontiersman turned conservationist who co-founded Scouting Burnham observed that fewer than 150 of these sheep lived in the Arizona mountains.
He called George F. Miller scout executive of the Boy Scout council headquartered in Phoenix, with a plan to save the sheep. Burnham put it this way: I want you to save this majestic animal, not only because it is in danger of extinction, but of more importance, some day it might provide domestic sheep with a strain to save them from disaster at the hands of a yet unknown virus. Several other prominent Arizonans joined the movement and a "save the bighorns" poster contest was started in schools throughout the state. Burnham appeared in store windows from one end of Arizona to the other; the contest-winning bighorn emblem was made into neckerchief slides for the 10,000 Boy Scouts, talks and dramatizations were given at school assemblies and on radio. The National Wildlife Federation, the Izaak Walton League, the Audubon Society joined the effort. On January 18, 1939, over 1.5 million acres were set aside at Kofa and at Cabeza Prieta National Wildlife Refuge combined, a civilian conservation corps side camp was set up to develop high mountain waterholes for the sheep.
On April 2, 1939, Kofa National Wildlife Refuge was opened. The desert bighorn sheep is now the official mascot for the Arizona Boy Scouts, the number of sheep in these parks have increased substantially; the Kofa Game Range, as it was called, was administered jointly by the U. S. Fish and Wildlife Service and the Bureau of Land Management. On February 5, 1975, Kofa was transferred to the Bureau of Land Management, but in 1976 complete authority was returned to the Department of Fish and Wildlife Services and the Kofa Game Range was renamed the Kofa National Wildlife Refuge. The population of desert bighorn sheep was estimated to be 428, they live in the two ranges that dominate the refuge landscape — the Kofa Mountains and Castle Dome Mountains of northern Yuma County and southern La Paz County. These mountains are not high, but they are rugged and rise from the surrounding desert plains, providing excellent bighorn sheep habitat. In recent years, this herd has provided animals for transplanting throughout Arizona and neighboring states.
Other notable wildlife species found in the area include desert tortoise and kit fox. Bird species that occur at Kofa include the white-winged dove, American kestrel, northern flicker, Say's phoebe, cactus wren and orange-crowned warbler. In recent years, the cougar has established a full-time presence in the park; the Kofa Mountain barberry, Berberis harrisoniana, a rare plant endemic to southwestern Arizona, occurs on the refuge. It is home to the desert fan palm, the only native palm in Arizona. Palm Canyon is a unique natural feature predominantly known for the native palm trees that grow in the canyon; these are rare in Arizona and are relicts of a geological period when the area was wetter and cooler. The turnoff for Palm Canyon is located at Milepost 85 on US Highway 95. A parking area is about eight miles east down a gravel road. Half a mile down the trail is a sign indicating the California fan palms; the hike to the canyon strenuous. The refuge provides opportunities for viewing desert plants and wildlife, rock climbing, exploring old mines, remote wilderness camping.
Temperatures exceed 120 °F in the summer, rain falls only a few times per year. Regulated hunting on the refuge is permitted for quail, bighorn sheep, cottontail rabbit and fox. Kofa was included in the desert military training exercises conducted by General George S. Patton during World War II. Unexploded ordnance may be encountered during cross-country hiking. List of flora of the Sonoran Desert Region by common name Fauna of the Sonoran Desert US Fish & Wildlife Service Kofa Wildlife Refuge website Kofa National Wildlife Refuge and Palm Canyon, Arizona Bird Checklists for Kofa Wildlife Refuge
The bobcat is a North American cat that appeared during the Irvingtonian stage of around 1.8 million years ago. Containing 2 recognized subspecies, it ranges from southern Canada to central Mexico, including most of the contiguous United States; the bobcat is an adaptable predator that inhabits wooded areas, as well as semidesert, urban edge, forest edge, swampland environments. It remains in some of its original range, but populations are vulnerable to local extinction by coyotes and domestic animals. With a gray to brown coat, whiskered face, black-tufted ears, the bobcat resembles the other species of the midsized genus Lynx, it is smaller on average than the Canada lynx, with which it shares parts of its range, but is about twice as large as the domestic cat. It has distinctive black bars on its forelegs and a black-tipped, stubby tail, from which it derives its name. Though the bobcat prefers rabbits and hares, it hunts insects, chickens and other birds, small rodents, deer. Prey selection depends on location and habitat and abundance.
Like most cats, the bobcat is territorial and solitary, although with some overlap in home ranges. It uses several methods to mark its territorial boundaries, including claw marks and deposits of urine or feces; the bobcat has a gestation period of about two months. Although bobcats have been hunted extensively by humans, both for sport and fur, their population has proven resilient though declining in some areas; the elusive predator features in the folklore of European settlers. There had been debate over whether to classify this species as Lynx rufus or Felis rufus as part of a wider issue regarding whether the four species of Lynx should be given their own genus, or be placed as a subgenus of Felis; the genus Lynx is now accepted, the bobcat is listed as Lynx rufus in modern taxonomic sources. Johnson et al. reported Lynx shared a clade with the puma, leopard cat, domestic cat lineages, dated to 7.15 million years ago. The bobcat is believed to have evolved from the Eurasian lynx, which crossed into North America by way of the Bering Land Bridge during the Pleistocene, with progenitors arriving as early as 2.6 million years ago.
The first wave moved into the southern portion of North America, soon cut off from the north by glaciers. This population evolved into modern bobcats around 20,000 years ago. A second population arrived from Asia and settled in the north, developing into the modern Canada lynx. Hybridization between the bobcat and the Canada lynx may sometimes occur. Thirteen bobcat subspecies have been recognized based on morphological characteristics: L. rufus rufus – eastern and midwestern United States L. r. gigas – northern New York to Nova Scotia and New Brunswick L. r. floridanus – southeastern United States and inland to the Mississippi valley, up to southwestern Missouri and southern Illinois L. r. superiorensis – western Great Lakes area, including upper Michigan, southern Ontario, most of Minnesota L. r. baileyi – southwestern United States and northwestern Mexico L. r. californicus – California west of the Sierra Nevada L. r. mohavensis – Mojave Desert of California L. r. escuinapae – central Mexico, with a northern extension along the west coast to southern Sonora L. r. fasciatus – Oregon, Washington west of the Cascade Range, northwestern California, southwestern British Columbia L. r. oaxacensis – Oaxaca L. r. pallescens – northwestern United States and southern British Columbia and Saskatchewan L. r. peninsularis – Baja California L. r. texensis – western Louisiana, south central Oklahoma, south into Tamaulipas, Nuevo León, CoahuilaThis subspecies division has been challenged, given a lack of clear geographic breaks in their ranges and the minor differences between subspecies.
The latest revision of cat taxonomy in 2017, by the Cat Classification Taskforce of the Cat Specialist Group recognises only two subspecies, based on phylogeographic and genetic studies, although the status of Mexican bobcats remains under review: Lynx rufus rufus – east of the Great Plains, North America Lynx rufus fasciatus – west of the Great Plains, North America The bobcat resembles other species of the genus Lynx, but is on average the smallest of the four. Its coat is variable, though tan to grayish-brown, with black streaks on the body and dark bars on the forelegs and tail, its spotted patterning acts as camouflage. The ears are pointed, with short, black tufts. An off-white color is seen on the lips and underparts. Bobcats in the desert regions of the southwest have the lightest-colored coats, while those in the northern, forested regions are darkest. Kittens are born well-furred and have their spots. A few melanistic bobcats have been captured in Florida, they may still exhibit a spot pattern.
The face appears wide due to ruffs of extended hair beneath the ears. Bobcat eyes are yellow with black pupils; the nose of the bobcat is pinkish-red, it has a base color of gray or yellowish- or brownish-red on its face and back. The pupils are round, black circles and will widen during nocturnal activity to maximize light reception; the cat has sharp hearing and vision, a good sense of smell. It is an excellent climber, swims when it needs to, but avoids water. However, cases of bobcats swimming long distances across lakes have been rec
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m