The nematodes or roundworms constitute the phylum Nematoda. They are a diverse animal phylum inhabiting a broad range of environments. Taxonomically, they are classified along with insects and other moulting animals in the clade Ecdysozoa, unlike flatworms, have tubular digestive systems with openings at both ends. Nematode species can be difficult to distinguish from one another. Estimates of the number of nematode species described to date vary by author and may change over time. A 2013 survey of animal biodiversity published in the mega journal Zootaxa puts this figure at over 25,000. Estimates of the total number of extant species are subject to greater variation. A referenced article published in 1993 estimated there may be over 1 million species of nematode, a claim which has since been repeated in numerous publications, without additional investigation, in an attempt to accentuate the importance and ubiquity of nematodes in the global ecosystem. Many other publications have since vigorously refuted this claim on the grounds that it is unsupported by fact, is the result of speculation and sensationalism.
More recent, fact-based estimates have placed the true figure closer to 40,000 species worldwide. Nematodes have adapted to nearly every ecosystem: from marine to fresh water, from the polar regions to the tropics, as well as the highest to the lowest of elevations, they are ubiquitous in freshwater and terrestrial environments, where they outnumber other animals in both individual and species counts, are found in locations as diverse as mountains and oceanic trenches. They are found in every part of the earth's lithosphere at great depths, 0.9–3.6 km below the surface of the Earth in gold mines in South Africa. They represent 90% of all animals on the ocean floor, their numerical dominance exceeding a million individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity of lifecycles, their presence at various trophic levels point to an important role in many ecosystems. They have been shown to play crucial roles in polar ecosystem; the 2,271 genera are placed in 256 families.
The many parasitic forms include pathogens in animals. A third of the genera occur as parasites of vertebrates. Nathan Cobb, a nematologist, described the ubiquity of nematodes on Earth as thus:In short, if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, if, as disembodied spirits, we could investigate it, we should find its mountains, vales, rivers and oceans represented by a film of nematodes; the location of towns would be decipherable, since for every massing of human beings, there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our highways; the location of the various plants and animals would still be decipherable, had we sufficient knowledge, in many cases their species could be determined by an examination of their erstwhile nematode parasites. Modern Latin compound of nemat- "thread" + -odes "like, of the nature of". In 1758, Linnaeus described some nematode genera included in the Vermes.
The name of the group Nematoda, informally called "nematodes", came from Nematoidea defined by Karl Rudolphi, from Ancient Greek νῆμα and -eiδἠς. It was treated as family Nematodes by Burmeister. At its origin, the "Nematoidea" erroneously included Nematodes and Nematomorpha, attributed by von Siebold. Along with Acanthocephala and Cestoidea, it formed the obsolete group Entozoa, created by Rudolphi, they were classed along with Acanthocephala in the obsolete phylum Nemathelminthes by Gegenbaur. In 1861, K. M. Diesing treated the group as order Nematoda. In 1877, the taxon Nematoidea, including the family Gordiidae, was promoted to the rank of phylum by Ray Lankester; the first clear distinction between the nemas and gordiids was realized by Vejdovsky when he named a group to contain the horsehair worms the order Nematomorpha. In 1919, Nathan Cobb proposed, he argued they should be called "nema" in English rather than "nematodes" and defined the taxon Nemates, listing Nematoidea sensu restricto as a synonym.
However, in 1910, Grobben proposed the phylum Aschelminthes and the nematodes were included in as class Nematoda along with class Rotifera, class Gastrotricha, class Kinorhyncha, class Priapulida, class Nematomorpha. In 1932, Potts elevated the class Nematoda to the level of phylum. Despite Potts' classification being equivalent to Cobbs', both names have been used and Nematode became a popular term in zoological science. Since Cobb was the first to include nematodes in a particular phylum separated from Nematomorpha, some researchers consider the valid taxon name to be Nemates or Nemata, rather than Nematoda, because of the zoological rule that gives priority to the first used term in case of synonyms; the phylogenetic relationships of the nematodes and their close relatives among the protostomian Metazoa are unresolved. Traditionally, they were held to b
Predation is a biological interaction where one organism, the predator and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation and parasitoidism, it is distinct from scavenging on dead prey, though many predators scavenge. Predators may search for prey or sit and wait for it; when prey is detected, the predator assesses. This may involve pursuit predation, sometimes after stalking the prey. If the attack is successful, the predator kills the prey, removes any inedible parts like the shell or spines, eats it. Predators are adapted and highly specialized for hunting, with acute senses such as vision, hearing, or smell. Many predatory animals, both vertebrate and invertebrate, have sharp claws or jaws to grip and cut up their prey. Other adaptations include aggressive mimicry that improve hunting efficiency. Predation has a powerful selective effect on prey, the prey develop antipredator adaptations such as warning coloration, alarm calls and other signals, mimicry of well-defended species, defensive spines and chemicals.
Sometimes predator and prey find themselves in an evolutionary arms race, a cycle of adaptations and counter-adaptations. Predation has been a major driver of evolution since at least the Cambrian period. At the most basic level, predators eat other organisms. However, the concept of predation is broad, defined differently in different contexts, includes a wide variety of feeding methods. A parasitoid, such as an ichneumon wasp, lays its eggs on its host. Zoologists call this a form of parasitism, though conventionally parasites are thought not to kill their hosts. A predator can be defined to differ from a parasitoid in two ways: it kills its prey immediately. There are other borderline cases. Micropredators are small animals that, like predators, feed on other organisms. However, since they do not kill their hosts, they are now thought of as parasites. Animals that graze on phytoplankton or mats of microbes are predators, as they consume and kill their food organisms. However, when animals eat seeds or eggs, they are consuming entire living organisms, which by definition makes them predators, albeit unconventional ones: for instance, a mouse that eats grass seeds has no adaptations for tracking and subduing prey and its teeth are not adapted to slicing through flesh.
Scavengers, organisms that only eat organisms found dead, are not predators, but many predators such as the jackal and the hyena scavenge when the opportunity arises. Among invertebrates, social wasps are both scavengers of other insects. While examples of predators among mammals and birds are well known, predators can be found in a broad range of taxa, they are common among insects, including mantids, dragonflies and scorpionflies. In some species such as the alderfly, only the larvae are predatory. Spiders are predatory, as well as other terrestrial invertebrates such as scorpions. In marine environments, most cnidarians, ctenophora and flatworms are predatory. Among crustaceans, crabs and barnacles are predators, in turn crustaceans are preyed on by nearly all cephalopods. Seed predation is restricted to mammals and insects and is found in all terrestrial ecosystems. Egg predation includes both specialist egg predators such as some colubrid snakes and generalists such as foxes and badgers that opportunistically take eggs when they find them.
Some plants, like the pitcher plant, the Venus fly trap and the sundew, are carnivorous and consume insects. Some carnivorous fungi catch nematodes using either active traps in the form of constricting rings, or passive traps with adhesive structures. Many species of protozoa and bacteria prey on other microorganisms. Among freshwater and marine zooplankton, whether single-celled or multi-cellular, predatory grazing on phytoplankton and smaller zooplankton is common, found in many species of nanoflagellates, ciliates, rotifers, a diverse range of meroplankton animal larvae, two groups of crustaceans, namely copepods and cladocerans. To feed, a predator must search for and kill its prey; these actions form a foraging cycle. The predator must decide. If it chooses pursuit, its physical capabilities determine the mode of pursuit. Having captured the prey, it may need to expend energy handling it (e.g. killing it, removing any shell or
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
Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans insects and other arthropods. Carnivorous plants have adapted to grow in places where the soil is thin or poor in nutrients nitrogen, such as acidic bogs. Charles Darwin wrote Insectivorous Plants, the first well-known treatise on carnivorous plants, in 1875. True carnivory is thought to have evolved independently nine times in five different orders of flowering plants, is represented by more than a dozen genera; this classification includes at least 583 species that attract and kill prey, absorbing the resulting available nutrients. Additionally, over 300 protocarnivorous plant species in several genera show some but not all of these characteristics. Five basic trapping mechanisms are found in carnivorous plants. Pitfall traps trap prey in a rolled leaf that contains a pool of digestive bacteria. Flypaper traps use a sticky mucilage. Snap traps utilize rapid leaf movements.
Bladder traps suck in prey with a bladder. Lobster traps known as eel traps, force prey to move towards a digestive organ with inward-pointing hairs; these traps may be passive, depending on whether movement aids the capture of prey. For example, Triphyophyllum is a passive flypaper that secretes mucilage, but whose leaves do not grow or move in response to prey capture. Meanwhile, sundews are active flypaper traps whose leaves undergo rapid acid growth, an expansion of individual cells as opposed to cell division; the rapid acid growth allows the sundew tentacles to bend, aiding in the retention and digestion of prey. The sundew species Drosera glanduligera employs a unique trapping mechanism with features of both flypaper and snap traps. Characterized by an internal chamber, pitfall traps are thought to have evolved independently at least six times; this particular adaptation is found within the families Sarraceniaceae, Nepenthaceae and Eriocaulaceae. Within the family Bromeliaceae, pitcher morphology and carnivory evolved twice.
Because these families do not share a common ancestor who had pitfall trap morphology, carnivorous pitchers are an example of convergent evolution. A passive trap, pitfall traps attract prey with nectar bribes secreted by the peristome and bright flower-like anthocyanin patterning within the pitcher; the linings of most pitcher plants are covered in a loose coating of waxy flakes which are slippery for insects, causing them to fall into the pitcher. Once within the pitcher structure, digestive enzymes or mutualistic species break down the prey into an absorbable form for the plant. Water can become trapped within the pitcher, making a habitat for other fauna; this type of'water body' is called a Phytotelma. The simplest pitcher plants are those of Heliamphora, the marsh pitcher plant. In this genus, the traps are derived from a simple rolled leaf whose margins have sealed together; these plants live in areas of high rainfall in South America such as Mount Roraima and have a problem ensuring their pitchers do not overflow.
To counteract this problem, natural selection has favoured the evolution of an overflow similar to that of a bathroom sink—a small gap in the zipped-up leaf margins allows excess water to flow out of the pitcher. Heliamphora is a member of a New World family in the order Ericales. Heliamphora is limited to South America, but the family contains two other genera and Darlingtonia, which are endemic to the Southeastern United States and California respectively. Sarracenia purpurea subsp. Purpurea can be found as far north as Canada. Sarracenia is the pitcher plant genus most encountered in cultivation, because it is hardy and easy to grow. In the genus Sarracenia, the problem of pitcher overflow is solved by an operculum, a flared leaflet that covers the opening of the rolled-leaf tube and protects it from rain; because of this improved waterproofing, Sarracenia species secrete enzymes such as proteases and phosphatases into the digestive fluid at the bottom of the pitcher. The enzymes digest the proteins and nucleic acids in the prey, releasing amino acids and phosphate ions, which the plant absorbs.
In at least one species, Sarracenia flava, the nectar bribe is laced with coniine, a toxic alkaloid found in hemlock, which increases the efficiency of the traps by intoxicating prey. Darlingtonia californica, the cobra plant, possesses an adaptation found in Sarracenia psittacina and, to a lesser extent, in Sarracenia minor: the operculum is balloon-like and seals the opening to the tube; this balloon-like chamber is pitted with areolae, chlorophyll-free patches through which light can penetrate. Insects ants, enter the chamber via the opening underneath the balloon. Once inside, they tire themselves trying to escape from these false exits, until they fall into the tube. Prey access is increased by the "fish tails", outgrowths of the operculum that give the plant its name; some seedling Sarracenia species have long, overhanging opercular outgrowths. The second major group of pitcher plants are the monkey cups or tropical pitcher plants of the genus Nepenthes. In the hundred or so species of this genus, the pitcher is borne at the end of a tendril, which grows as an extension to the midrib o
Felidae is a family of mammals in the order Carnivora, colloquially referred to as cats. A member of this family is called a felid; the term "cat" refers both to felids in general and to the domestic cat. The Felidae species exhibit the most diverse fur pattern of all terrestrial carnivores. Cats have slender muscular bodies and strong flexible forelimbs, their teeth and facial muscles allow for a powerful bite. They are all obligate carnivores, most are solitary predators ambushing or stalking their prey. Wild cats occur in Africa, Europe and the Americas; some wild cat species are adapted to forest habitats, some to arid environments, a few to wetlands and mountainous terrain. Their activity patterns range from nocturnal and crepuscular to diurnal, depending on their preferred prey species. Reginald Innes Pocock divided the extant Felidae into three subfamilies: the Pantherinae, the Felinae and the Acinonychinae, differing from each other by the ossification of the hyoid apparatus and by the cutaneous sheaths which protect their claws.
This concept has been revised following developments in molecular biology and techniques for analysis of morphological data. Today, the living Felidae are divided in two subfamilies, with the Pantherinae including seven Panthera and two Neofelis species; the Felinae include all the non-pantherine cats with 34 species. The first cats emerged during the Oligocene about 25 million years ago, with the appearance of Proailurus and Pseudaelurus; the latter species complex was ancestral to two main lines of felids: the cats in the extant subfamilies and a group of extinct cats of the subfamily Machairodontinae, which include the saber-toothed cats such as the Smilodon. The "false sabre toothed cats", the Barbourofelidae and Nimravidae, are not true cats, but are related. Together with the Felidae, Viverridae and mongooses, they constitute the Feliformia. All members of the cat family have the following characteristics in common: They are digitigrade, have five toes on their forefeet and four on their hind feet.
Their curved claws are protractile and attached to the terminal bones of the toe with ligaments and tendons. The claws are guarded except in the Acinonyx, they protract the claws by contracting muscles in the toe, they passively retract them. The dewclaws do not protract, they have 30 teeth with a dental formula of 22.214.171.124.1.2.1. The upper third premolar and lower molar are adapted as carnassial teeth, suited to tearing and cutting flesh; the canine teeth are large. The lower carnassial is smaller than the upper carnassial and has a crown with two compressed blade-like pointed cusps, their nose projects beyond the lower jaw. They have well developed and sensitive whiskers above the eyes, on the cheeks, on the muzzle, but not below the chin. Whiskers help to capture and hold prey, their skull is foreshortened with large orbits. Their tongue is covered with horny papillae, which rasp meat from aid in grooming, their eyes are large, situated to provide binocular vision. Their night vision is good due to the presence of a tapetum lucidum, which reflects light back inside the eyeball, gives felid eyes their distinctive shine.
As a result, the eyes of felids are about six times more light sensitive than those of humans, many species are at least nocturnal. The retina of felids contains a high proportion of rod cells, adapted for distinguishing moving objects in conditions of dim light, which are complemented by the presence of cone cells for sensing colour during the day, their external ears are large, sensitive to high-frequency sounds in the smaller cat species. This sensitivity allows them to locate small rodent prey, they have flexible bodies with muscular limbs. The plantar pads of both fore and hind feet form compact three-lobed cushions; the penis is boneless. Relative to body size, they have shorter bacula than canids, they can not detect the sweetness of sugar. Felids have a vomeronasal organ in the roof of the mouth; the use of this organ is associated with the Flehmen response. The standard sounds made by all felids include meowing, hissing and growling. Meowing is the main contact sound, they can purr during both phases of respiration, though pantherine cats seem to purr only during oestrus and copulation, as cubs when suckling.
Purring is a low pitch sound of less than 2 kHz and mixed with other vocalization types during the expiratory phase. Most felids are able to land on their feet after a fall due to the cat righting reflex; the colour and density of their fur is diverse. Fur colour varies from light brown to golden and reddish brown, fur pattern from distinctive small spots, stripes to small blotches and rosettes. Most cat species are born except the jaguarundi, Asian golden cat and caracal; the spotted fur of lion and cougar cubs change to a uniform fur during their ontogeny. Those living in cold environments have thick fur with long hair, like the snow leopard and the Pallas's cat; those living in tropical and hot climate zones have short fur. Several species exhibit melanism with all-black individuals. In the great majority of cat species, the tail is between a third and a half of the body length, although with some exceptions, like the Ly
The African buffalo or Cape buffalo is a large Sub-Saharan African bovine. Syncerus caffer caffer, the Cape buffalo, is the typical subspecies, the largest one, found in Southern and East Africa. S. c. nanus is the smallest subspecies, common in forest areas of Central and West Africa, while S. c. brachyceros is in West Africa and S. c. aequinoctialis is in the savannas of East Africa. The adult buffalo's horns are its characteristic feature: they have fused bases, forming a continuous bone shield across the top of the head referred to as a "boss", they are regarded as among the most dangerous animals on the African continent, according to some estimates they gore and kill over 200 people every year. The African buffalo is not an ancestor of domestic cattle and is only distantly related to other larger bovines, its unpredictable temperament means that the African buffalo has never been domesticated, unlike its Asian counterpart, the water buffalo. African Cape buffaloes have few predators aside from large crocodiles.
As a member of the big five game, the Cape buffalo is a sought-after trophy in hunting. The African buffalo is a robust species, its shoulder height can range from 1.0 to 1.7 m and its head-and-body length can range from 1.7 to 3.4 m. Compared with other large bovids, it has a long but stocky body and short but thickset legs, resulting in a short standing height; the tail can range from 70 to 110 cm long. Savannah-type buffaloes weigh 500 to 1,000 kg, with males larger than females, reaching the upper weight range. In comparison, forest-type buffaloes, at 250 to 450 kg, are only half that size, its head is carried low. The front hooves of the buffalo are wider than the rear, associated with the need to support the weight of the front part of the body, heavier and more powerful than the back. Savannah-type buffaloes have dark brown coats with age. Old bulls have whitish circles around their eyes and on their face. Females tend to have more-reddish coats. Forest-type buffaloes are 30-40% smaller, reddish brown in colour, with much more hair growth around the ears and with horns that curve back and up.
Calves of both types have red coats. A characteristic feature of the horns of adult male African buffalo is that the bases come close together, forming a shield referred to as a "boss". From the base, the horns diverge downwards smoothly curve upwards and outwards and in some cases inwards and or backwards. In large bulls, the distance between the ends of the horns can reach upwards of one metre; the horns form when the animal reaches the age of five or six years but the bosses do not become "hard" till 8 to 9 years old. In cows, the horns are, on average, 10–20% smaller, they do not have a boss. Forest buffalo horns are smaller than those of the savanna buffalo from Southern and Eastern Africa measuring less than 40 centimetres, are never fused. Syncerus caffer caffer is the nominate subspecies and the largest one, with large males weighing up to 910 kg; the average weight of bulls from South Africa was 753 kg. In Serengeti National Park, eight bulls averaged 751 kg. Mature cows from Kruger National Park averaged 513 kg.
In both Kenya and Botswana, the average adult weight of this race was estimated as 631 kg. It is peculiar to East Africa. Buffaloes of this subspecies living in the south of the continent, notably tall in size and ferocity, are the so-called Cape buffalo. Color of this subspecies is the darkest black. S. c. nanus is the smallest of the subspecies. The color is red, with darker patches on the head and shoulders, in the ears, forming a brush; the dwarf buffalo is common in forest areas of West Africa. This subspecies is so different from the nominate subspecies that some researchers still consider it to be a separate species, S. nanus. Hybrids between the nominate and dwarf subspecies are not uncommon. S. c. brachyceros is, in morphological terms, intermediate between the first two subspecies. It occurs in West Africa, its dimensions are small compared to other buffalo found in Cameroon, which weigh half as much as the Cape subspecies. Adults average in weight up to 400 kg. S. c. aequinoctialis is confined to the savannas of Central Africa.
It is similar to the Cape buffalo, but somewhat smaller, its color is lighter. This subspecies is sometimes considered to be the same as the Sudanese buffalo. S. c. mathewsi is not universally recognized by all authorities. It lives in mountainous areas of the Democratic Republic of the Congo and Uganda; the African buffalo is one of the most successful grazers in Africa. It lives in swamps and floodplains, as well as mopane grasslands, the forests of the major mountains of Africa; this buffalo prefers a habitat with dense cover, such as reeds and thickets, but can be found in open woodland. While not demanding in regards to their habitat, they require water daily, so they depend on perenn
The Bengal tiger is a Panthera tigris tigris population in the Indian subcontinent. It is listed as Endangered on the IUCN Red List since 2008, was estimated at comprising fewer than 2,500 individuals by 2011, it is threatened by poaching and fragmentation of habitat. None of the Tiger Conservation Landscapes within its range is considered large enough to support an effective population of more than 250 adult individuals. India's tiger population was estimated at 1,706–1,909 individuals in 2010. By 2014, the population had reputedly increased to an estimated 2,226 individuals. Around 440 tigers are estimated in 103 tigers in Bhutan; the tiger is estimated to be present in the Indian subcontinent since the Late Pleistocene, for about 12,000 to 16,500 years. The Bengal tiger ranks among the biggest wild cats alive today, it is considered to belong to the world's charismatic megafauna. It is the national animal of both Bangladesh, it is known as the Royal Bengal tiger. Felis tigris was the scientific name used by Carl Linnaeus in 1758 for the tiger.
It was subordinated to the genus Panthera by Reginald Innes Pocock in 1929. Bengal is the traditional type locality of the species and the nominate subspecies Panthera tigris tigris; the validity of several tiger subspecies in continental Asia was questioned in 1999. Morphologically, tigers from different regions vary little, gene flow between populations in those regions is considered to have been possible during the Pleistocene. Therefore, it was proposed to recognize only two subspecies as valid, namely P. t. tigris in mainland Asia, P. t. sondaica in the Greater Sunda Islands and in Sundaland. The extinct and living tiger populations in continental Asia have been subsumed to P. t. tigris since the revision of felid taxonomy in 2017. The Bengal tiger is defined by three distinct mitochondrial nucleotide sites and 12 unique microsatellite alleles; the pattern of genetic variation in the Bengal tiger corresponds to the premise that it arrived in India 12,000 years ago. This is consistent with the lack of tiger fossils from the Indian subcontinent prior to the late Pleistocene, the absence of tigers from Sri Lanka, separated from the subcontinent by rising sea levels in the early Holocene.
The Bengal tiger's coat is yellow to light orange, with stripes ranging from dark brown to black. The white tiger is a recessive mutant of the tiger, reported in the wild from time to time in Assam, Bengal and from the former State of Rewa. However, it is not to be mistaken as an occurrence of albinism. In fact, there is only one authenticated case of a true albino tiger, none of black tigers, with the possible exception of one dead specimen examined in Chittagong in 1846. Males have an average total length of 270 to 310 cm including the tail, while females measure 240 to 265 cm on average; the tail is 85 to 110 cm long, on average, tigers are 90 to 110 cm in height at the shoulders. The weight of males ranges from 180 to 258 kg; the smallest recorded weights for Bengal tigers are from the Bangladesh Sundarbans, where adult females are 75 to 80 kg. The tiger has exceptionally stout teeth, its canines are 7.5 to 10 cm long and thus the longest among all cats. The greatest length of its skull is 332 to 376 mm. Bengal tigers weigh up to 325 kg, reach a head and body length of 320 cm.
Several scientists indicated that adult male Bengal tigers from the Terai in Nepal and Bhutan, Assam and West Bengal in north India attain more than 227 kg of body weight. Seven adult males captured in Chitwan National Park in the early 1970s had an average weight of 235 kg ranging from 200 to 261 kg, that of the females was 140 kg ranging from 116 to 164 kg. Thus, the Bengal tiger rivals the Amur tiger in average weight. In addition, the record for the greatest length of a tiger skull was an "over the bone" length of 16.25 in. Verifiable Sundarbans tiger weights are not found in any scientific literature. Forest Department records list weight measurements. There are reports of head and body lengths, some of which are listed as over 366 cm. More researchers from the University of Minnesota and the Bangladesh Forest Department carried out a study for the US Fish and Wildlife Service and weighed three Sundarbans tigresses from Bangladesh. Two of them were captured and sedated for radio-collaring, the other one had been killed by local villagers.
The two collared tigresses were weighed using 150 kg scales, the tigress killed by villagers was weighed using a balance scale and weights. The three tigresses had a mean weight of 76.7 kg. One of the two older female's weight 75 kg weighed less than the mean because of her old age and poor condition at the time of capture; the teeth wear of the two radio-collared females indicated that they were between 12 and 14 years old. The tigress killed by the villagers was a young adult between 3 and 4 years old, she was a pre-territorial transient. Skulls and body weights of Sundarbans tigers were found to be distinct from tigers in other habitats, indicating that they may have adapted to the unique conditions of the mangrove habitat, their small sizes are due to a combination of