Birds known as Aves, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, a strong yet lightweight skeleton. Birds range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the world's most numerically-successful class of tetrapods, with ten thousand living species, more than half of these being passerines, sometimes known as perching birds. Birds have wings which are less developed depending on the species. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in flightless birds, including ratites and diverse endemic island species of birds; the digestive and respiratory systems of birds are uniquely adapted for flight. Some bird species of aquatic environments seabirds and some waterbirds, have further evolved for swimming; the fossil record demonstrates that birds are modern feathered dinosaurs, having evolved from earlier feathered dinosaurs within the theropod group, which are traditionally placed within the saurischian dinosaurs.
The closest living relatives of birds are the crocodilians. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago. Many of these early "stem-birds", such as Archaeopteryx, were not yet capable of powered flight, many retained primitive characteristics like toothy jaws in place of beaks, long bony tails. DNA-based evidence finds that birds diversified around the time of the Cretaceous–Palaeogene extinction event 66 million years ago, which killed off the pterosaurs and all the non-avian dinosaur lineages, but birds those in the southern continents, survived this event and migrated to other parts of the world while diversifying during periods of global cooling. This makes them the sole surviving dinosaurs according to cladistics; some birds corvids and parrots, are among the most intelligent animals. Many species annually migrate great distances. Birds are social, communicating with visual signals and bird songs, participating in such social behaviours as cooperative breeding and hunting and mobbing of predators.
The vast majority of bird species are monogamous for one breeding season at a time, sometimes for years, but for life. Other species have breeding systems that are polygynous or polyandrous. Birds produce offspring by laying eggs, they are laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching; some birds, such as hens, lay eggs when not fertilised, though unfertilised eggs do not produce offspring. Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs and feathers. Songbirds and other species are popular as pets. Guano is harvested for use as a fertiliser. Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them.
Recreational birdwatching is an important part of the ecotourism industry. The first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae. Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system in use. Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda. Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica. However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, is used by many scientists including adherents of the Phylocode system. Gauthier defined Aves to include only the crown group of the set of modern birds; this was done by excluding most groups known only from fossils, assigning them, instead, to the Avialae, in part to avoid the uncertainties about the placement of Archaeopteryx in relation to animals traditionally thought of as theropod dinosaurs.
Gauthier identified four different definitions for the same biological name "Aves", a problem. Gauthier proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below, he assigned other names to the other groups. Aves can mean all archosaurs closer to birds than to crocodiles Aves can mean those advanced archosaurs with feathers Aves can mean those feathered dinosaurs that fly Aves can mean the last common ancestor of all the living birds and all of its descendants (a "c
A newt is a salamander in the subfamily Pleurodelinae called eft during its terrestrial juvenile phase. Unlike other members of the family Salamandridae, newts are semiaquatic, alternating between aquatic and terrestrial habitats over the year, sometimes staying in the water full-time. Not all aquatic salamanders are considered newts, however. More than 100 known species of newts are found in North America, North Africa and Asia. Newts metamorphose through three distinct developmental life stages: aquatic larva, terrestrial juvenile, adult. Adult newts have lizard-like bodies and return to the water every year to breed, otherwise living in humid, cover-rich land habitats. Newts are threatened by habitat loss and pollution. Several species are endangered, at least one species, the Yunnan lake newt, has gone extinct recently; the Old English name of the animal was efte, resulting in Middle English eft. The initial'n' was added from the indefinite article'an' by provection by the early 15th century.
The form'newt' appears to have arisen as a dialectal variant of eft in Staffordshire, but entered Standard English by the Early Modern period. The regular form eft, now only used for newly metamorphosed specimens, survived alongside newt in composition, the larva being called "water-eft" and the mature form "land-eft" well into the 18th century, but the simplex "eft" as equivalent to "water-eft" has been in use since at least the 17th century. Dialectal English and Scots has the word ask used for both newts and wall lizards, from Old English āþexe, from Proto-Germanic *agiþahsijǭ "lizard-badger" or "distaff-like lizard". Latin had the name stellio for a type of spotted newt, now used for species of the genus Stellagama. Ancient Greek had the name κορδύλος for the water newt. German has Molch, from Middle High German wikt: olm, like the English term of unknown etymology. Newts are known as Tritones in historical literature, "triton" remains in use as common name in some Romance languages, in Greek, in Romanian and Bulgarian.
The systematic name Tritones was introduced alongside Pleurodelinae by Tschudi in 1838, based on the type genus named Triton by Laurenti in 1768. Laurenti's Triton was renamed to Triturus by Rafinesque in 1815. Tschudi's Pleurodelinae is based on the type genus Pleurodeles named by Michahelles in 1830. Newts are found in North America, North Africa and Asia; the Pacific newts and the Eastern newts with together seven species are the only representatives in North America, while most diversity is found in the Old World: In Europe and the Middle East, the group's origin, eight genera with 30 species are found, with the ribbed newts extending to northernmost Africa. Eastern Asia, from Eastern India over Indochina to Japan, is home to five genera with more than 40 species. Newts are semiaquatic, spending part of the year in the water for reproduction and the rest of the year on land. While most species prefer stagnant water bodies such as ponds, ditches or flooded meadows for reproduction, some species such as the Danube crested newt can occur in slow-flowing rivers.
The European brook newts and European mountain newts have adapted to life in cold, oxygen-rich mountain streams. During their terrestrial phase, newts live in humid habitats with abundant cover such as logs, rocks, or earth holes. Newts share many of the characteristics of their salamander kin, including semipermeable glandular skin, four equal-sized limbs, a distinct tail; the newt's skin, however, is not as smooth as that of other salamanders. Aquatic larvae have true teeth on both upper and lower jaws, external gills, they have the ability to regenerate limbs, spinal cords, hearts and upper and lower jaws. The Japanese fire belly newt can regenerate its eye lens 18 times over a period of 16 years and retain its structural and functional properties; the cells at the site of the injury have the ability to undifferentiate and differentiate again to create a new limb or organ. One hypothesis is that the undifferentiated cells are related to tumour cells, since chemicals that produce tumours in other animals will produce additional limbs in newts.
The main breeding season for newts is in July. After courtship rituals of varying complexity, which take place in ponds or slow-moving streams, the male newt transfers a spermatophore, taken up by the female. Fertilized eggs are laid singly and are attached to aquatic plants; this distinguishes them from the free-floating eggs of frogs or toads, which are laid in clumps or in strings. Plant leaves are folded over and attached to the eggs to protect them; the larvae, which resemble fish fry but are distinguished by their feathery external gills, hatch out in about three weeks. After hatching, they eat small invertebrates, or other amphibian larvae. During the subsequent few months, the larvae undergo metamorphosis, during which they develop legs, the gills are absorbed and replaced by air-breathing lungs; some species, such as the North American newts become more brightly coloured during this phase. Once metamor
A tadpole is the larval stage in the life cycle of an amphibian that of a frog or toad. They are wholly aquatic, though some species have tadpoles that are terrestrial; when first hatched from the egg they have a more or less globular body, a laterally compressed tail and internal or external gills. As they grow they undergo metamorphosis, during which process they grow limbs, develop lungs and reabsorb the tail. Most tadpoles are herbivorous and during metamorphosis the mouth and internal organs are rearranged to prepare for an adult carnivorous lifestyle. Having no hard parts, it might be expected. However, traces of biofilms have been preserved and fossil tadpoles have been found dating back to the Miocene. Tadpoles are eaten in some parts of the world and are mentioned in folk tales and used as a symbol in ancient Egyptian numerals; the name "tadpole" is from Middle English taddepol, made up of the elements tadde, "toad", pol, "head". "pollywog" / "polliwog" is from Middle English polwygle, made up of the same pol, "head", wiglen, "to wiggle".
Tadpoles are young amphibians that live in the water, though a few tadpoles are semi-terrestrial and terrestrial. During the tadpole stage of the amphibian life cycle, most respire by means of autonomous external or internal gills, they do not have arms or legs until the transition to adulthood, have a large, flattened tail with which they swim by lateral undulation, similar to most fish. As a tadpole matures, it most metamorphosizes by growing limbs and outwardly absorbing its tail by apoptosis. Lungs develop around the time of leg development, tadpoles late in development will be found near the surface of the water, where they breathe air. During the final stages of external metamorphosis, the tadpole's mouth changes from a small, enclosed mouth at the front of the head to a large mouth the same width as the head; the intestines shorten to accommodate the new diet. Most tadpoles are herbivorous; some species are omnivorous. Tadpoles vary in size, both during their development and between species.
For example, in a single family, length of late-stage tadpoles varies between 33 millimetres and 106 millimetres. The tadpoles of Pseudis paradoxa grow to the largest of any frog. Despite their soft-bodied nature and lack of mineralised hard parts, fossil tadpoles have been recovered from Upper Miocene strata, they are preserved with more robust structures preserved as a carbon film. In Miocene fossils from Libros, the brain case is preserved in calcium carbonate, the nerve cord in calcium phosphate. Other parts of the tadpoles' bodies exist as organic remains and bacterial biofilms, with sedimentary detritus present in the gut. Tadpole remains with telltale external gills are known from several labyrinthodont groups; some tadpoles are used as food. Tadpoles of megophryid frog Oreolalax rhodostigmatus are large, more than 10 cm in length, are collected for human consumption in China. In India, Clinotarsus curtipes are collected for food, in Peru at least Telmatobius mayoloi tadpoles are collected for food and medicine.
According to Sir George Scott, in the origin myths of the Wa people in China and Myanmar, the first Wa originated from two female ancestors Ya Htawm and Ya Htai, who spent their early phase as tadpoles in a lake in the Wa country known as Nawng Hkaeo. In the Ancient Egyptian numerals, a hieroglyphic representing a tadpole was used to denote the value of 100,000. McDiarmid, Roy W.. Tadpoles: the Biology of Anuran Larvae. Chicago: University of Chicago Press. ISBN 0226557634
Hawksbill sea turtle
The hawksbill sea turtle is a Critically Endangered sea turtle belonging to the family Cheloniidae. It is the only extant species in the genus Eretmochelys; the species has a worldwide distribution, with Atlantic and Indo-Pacific subspecies—E. I. imbricata and E. i. bissa, respectively. The hawksbill's appearance is similar to that of other marine turtles. In general, it has a flattened body shape, a protective carapace, flipper-like limbs, adapted for swimming in the open ocean. E. imbricata is distinguished from other sea turtles by its sharp, curving beak with prominent tomium, the saw-like appearance of its shell margins. Hawksbill shells change colors, depending on water temperature. While this turtle lives part of its life in the open ocean, it spends more time in shallow lagoons and coral reefs; the World Conservation Union as a result of Human fishing practices, classifies E. imbricata as critically endangered. Hawksbill shells were the primary source of tortoiseshell material used for decorative purposes.
The Convention on International Trade in Endangered Species outlaws the capture and trade of hawksbill sea turtles and products derived from them. Adult hawksbill sea turtles grow to 1 m in length, weighing around 80 kg on average; the heaviest hawksbill captured weighed 127 kg. The turtle's shell, or carapace, has an amber background patterned with an irregular combination of light and dark streaks, with predominantly black and mottled-brown colors radiating to the sides. Several characteristics of the hawksbill sea turtle distinguish it from other sea turtle species, its elongated, tapered head ends in a beak-like mouth, its beak is more pronounced and hooked than others. The hawksbill's forelimbs have two visible claws on each flipper. One of the hawksbill's more distinguished characteristics is the pattern of thick scutes that make up its carapace. While its carapace has five central scutes and four pairs of lateral scutes like several members of its family, E. imbricata's posterior scutes overlap in such a way as to give the rear margin of its carapace a serrated look, similar to the edge of a saw or a steak knife.
The turtle's carapace has been known to reach 1 m in length. The hawksbill appears to employ its sturdy shell to insert its body into tight spaces in reefs. Crawling with an alternating gait, hawksbill tracks left in the sand are asymmetrical. In contrast, the green sea turtle and the leatherback turtle have a more symmetrical gait. Due to its consumption of venomous cnidarians, hawksbill sea turtle flesh can become toxic; the hawksbill sea turtle has been shown to be biofluorescent and is the first reptile recorded with this characteristic. It is unknown if this is derived from the turtle's diet, which includes biofluorescent organisms like the hard coral Physogyra lichtensteini. Males have more intense pigmentation than females, a behavioural role of these differences is speculated. Hawksbill sea turtles have a wide range, found predominantly in tropical reefs of the Indian and Atlantic Oceans. Of all the sea turtle species, E. imbricata is the one most associated with warm tropical waters. Two major subpopulations are known, in the Indo-Pacific.
In the Atlantic, hawksbill populations range as far west as the Gulf of Mexico and as far southeast as the Cape of Good Hope in South Africa. They live off the waters off Virginia. In the Caribbean, the main nesting beaches are in the Lesser Antilles, Guadeloupe, Tortuguero in Costa Rica, in the Yucatan, they feed in the waters around Mona Island near Puerto Rico among other places. In the Indian Ocean, hawksbills are a common sight along the east coast of Africa, including the seas surrounding Madagascar and nearby island groups, all along the southern Asian coast, including the Persian Gulf, the Red Sea, the coasts of the Indian Subcontinent and Southeast Asia, they are present across the Malay northern Australia. Their Pacific range is limited to the ocean's subtropical regions. In the west, it extends from the southwestern tips of the Korean Peninsula and the Japanese Archipelago south to northern New Zealand; the Philippines hosts several nesting sites, including the island of Boracay and Punta Dumalag in Davao City.
Dahican Beach in Mati City, Davao Oriental hosts one of the most important hatcheries of its kind along with Olive Riley Turtles in the archipelagic country of the Philippines. A small group of islands in the southwest of the archipelago has been named the "Turtle Islands" because two species of sea turtles nest there: the hawksbill and the green sea turtle. In January 2016, a juvenile was seen in Gulf of Thailand. A 2018 article by The Straits Times reported that around 120 hawksbill juvenile turtles hatched at Pulau Satumu, Singapore. Found in Singapore waters, hawksbill turtles have returned to areas such East Coast Park and Palau Satumu to nest. In Hawaii, hawksbills nest on the "main" islands of Oahu, Maui and Hawaii. In Australia, hawksbills are known to nest on Milman Island in the Great Barrier Reef. Hawksbill sea turtles nest as far west as Cousine Island in the Seychelles, where the species has been protected since 1994, the population is showing some recovery; the Seychelles' inner islands and islets, such as Aldabra, are popular feeding grounds for immature hawksbills.
In the eastern Pacific, hawksbills are known to occur from the Baja Peninsula in Mexico south along the coast to southern Peru. Nonetheless, as as 2007, the species had been considered extirpated in the re
Monotremes are one of the three main groups of living mammals, along with placentals and marsupials. The monotremes are typified by structural differences in their brains, digestive tract, reproductive tract, other body parts compared to the more common mammalian types. In addition they lay eggs rather than bear live young, like marsupials, they store their newly hatched, larvae-like, developing puggles in a pouch, like all mammals, the female monotremes nurse their young with milk. Monotremes are traditionally referred to as the mammalian subclass Prototheria; the only surviving examples of monotremes are all indigenous to Australia and New Guinea although there is evidence that they were once more widespread including some extinct species in South America. The existing monotreme species are four species of echidnas. There is some debate regarding monotreme taxonomy. Like other mammals, monotremes are endothermic with a high metabolic rate. In common with reptiles and marsupials, monotremes lack the connective structure which in placental mammals is the primary communication route between the right and left brain hemispheres.
The anterior commissure does provide an alternate communication route between the two hemispheres, in monotremes and marsupials it carries all the commissural fibers arising from the neocortex, whereas in placental mammals the anterior commissure carries only some of these fibers. Extant monotremes lack teeth as adults. Fossil forms and modern platypus young have a "tribosphenic" form of molars, one of the hallmarks of extant mammals; some recent work suggests that monotremes acquired this form of molar independently of placental mammals and marsupials, although this hypothesis remains disputed. Tooth loss in modern monotremes might be related to their development of electrolocation. Monotreme jaws are constructed somewhat differently from those of other mammals, the jaw opening muscle is different; as in all true mammals, the tiny bones that conduct sound to the inner ear are incorporated into the skull, rather than lying in the jaw as in cynodonts and other premammalian synapsids. Nonetheless, findings on the extinct species Teinolophos confirm that suspended ear bones evolved independently among monotremes and therians.
The external opening of the ear still lies at the base of the jaw. The sequencing of the platypus genome has provided insight into the evolution of a number of monotreme traits, such as venom and electroreception, as well as showing some new unique features, such as the fact that monotremes possess 5 pairs of sex chromosomes and that one of the X chromosomes resembles the Z chromosome of birds, suggesting that the two sex chromosomes of marsupial and placental mammals evolved after the split from the monotreme lineage. Additional reconstruction through shared genes in sex chromosomes supports this hypothesis of independent evolution; this feature, along with some other genetic similarities with birds, such as shared genes related to egg-laying, is thought to provide some insight into the most recent common ancestor of the synapsid lineage leading to mammals and the sauropsid lineage leading to birds and modern reptiles, which are believed to have split about 315 million years ago during the Carboniferous.
The presence of vitellogenin genes is shared with birds. DNA analyses suggest that although this trait is shared and is synapomorphic with birds, platypuses are still mammals and that the common ancestor of extant mammals lactated. L-ascorbic acid is synthesized only in the kidneys; the monotremes have extra bones in the shoulder girdle, including an interclavicle and coracoid, which are not found in other mammals. Monotremes retain a reptile-like gait, with legs on the sides of, rather than underneath, their bodies; the monotreme leg bears a spur in the ankle region. This venom is derived from b-defensins, proteins that are present in mammals that create holes in viral and bacterial pathogens; some reptile venom is composed of different types of b-defensins, another trait shared with reptiles. It is thought to be an ancient mammalian characteristic, as many non-monotreme archaic mammal groups possess venomous spurs; the key anatomical difference between monotremes and other mammals gives them their name.
Monotremes, like reptiles, have a single cloaca. In monotremes, only semen passes through the penis; the monotreme penis is similar to that of turtles, is covered by a preputial sac. Monotreme eggs are retained for some time within the mot
In biology, precocial species are those in which the young are mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called "altricial", where the young are born or hatched helpless; these categories form a continuum, without distinct gaps between them. Precocial species are nidifugous, meaning that they leave the nest shortly after birth or hatching; the span between precocial and altricial species is broad in birds. Precocial birds hatch with their eyes open and are covered with downy feathers that are soon replaced by adult-type feathers. Birds of this kind can swim and run much sooner after hatching than altricial young, such as songbirds. Precocial birds can be ready to leave the nest in a short period of time following hatching. Many precocial chicks are not independent in thermoregulation, they depend on the attending parent to brood them with body heat for a short period of time. Precocial birds find their own food, sometimes with instruction from the parents.
Examples of precocial birds include the domestic chicken, many species of ducks and geese, waders and the hoatzin. Precociality is found in many other animal groups. Familiar examples of precocial mammals are most ungulates, the guinea pig, most species of hare; this last example is significant as it illustrates that precociality is not a conservative characteristic, in the evolutionary sense, since the related rabbit is altricial. Precocial species have a longer gestation or incubation period than related altricial species, smaller litters or clutches, since each offspring has to be brought to a advanced state before birth or hatching; the phenomenon of imprinting studied by Konrad Lorenz is characteristic of precocial birds. Precocial species are called "superprecocial". Examples are the megapode birds, which have full flight feathers and which, in some species, can fly on the same day they hatch from their eggs. Another example is the blue wildebeest, whose calves can stand within an average of six minutes from birth and walk within thirty minutes.
Such behavior gives them an advantage over other herbivore species. Hartebeest calves are not as precocial as wildebeest calves and take up to thirty minutes or more before they stand, as long as forty-five minutes before they can follow their mothers for short distances, they are unable to keep up with their mothers. The word "precocial" is derived from the same root as precocious, implying in both cases early maturity. Precociality is thought to be ancestral in birds. Thus, altricial birds tend to be found in the most derived groups. There is some evidence for precociality in troodontids. Precocious puberty Parental investment Starck J. M. Ricklefs R. E.. "Patterns of Development: The Altricial – Precocial Spectrum". Avian Growth and Development. New York: Oxford University Press
In biology, altricial species are those in which the young are incapable of moving around on their own soon after hatching or being born. The word is derived from the Latin root alere, meaning "to nurse, to rear, or to nourish" and indicates the need for young to be fed and taken care of for a long duration. Species whose young are or mobile are called precocial. In bird and mammal biology, altricial species are those species whose newly hatched or born young are immobile, lack hair or down, are not able to obtain food on their own, must be cared for by adults. Altricial young require care for a length of time. Among birds, these include herons, woodpeckers, owls and most passerines. Among mammals and most rodents are altricial. Domestic cats and humans are some of the best-known altricial organisms. For example, newborn domestic cats cannot see, maintain their own body temperature, or gag, require external stimulation to defecate and urinate; the larvae of some insects may be considered altricial as well.
In particular, the larvae of eusocial insects such as ants and wasps are immobile and helpless grubs that are dependent on the workers tending to them. At the opposite end of the spectrum are precocial animals in which the young have open eyes, have hair or down, have large brains, are mobile and somewhat able to flee from, or defend themselves against, predators. For example, with ground-nesting birds such as ducks or turkeys, the young are ready to leave the nest in one or two days. Among mammals, most ungulates are precocial, being able to walk immediately after birth. Beyond the precocial are the superprecocial animals, such as the megapode birds, which hatch with full flight feathers. Different animals employ different altricial strategies; the ability of the parents to obtain nutrition and contribute to the pre-natal and post-natal development of their young appears to be associated. Precocial birds are able to provide protein-rich eggs and thus their young hatch in the fledgling stage – able to protect themselves from predators and the females have less post-natal involvement.
Altricial birds are less able to contribute nutrients in the pre-natal stage. This may be related to r/K selection. In birds, altricial young grow faster than precocial young; this is hypothesized to occur so that exposure to predators during the nestling stage of development can be minimized. In the case of mammals it has been suggested that large adult body sizes favor production of large, precocious young, which develop with a long gestation period. Large young may be associated with long lifespan, extended reproductive period, reduced litter size, it has been suggested that altricial strategies in mammals may be favoured if there is a selective advantage to mothers that are capable of resorbing embryos in early stages of development. Some ecological niches require young to be precocial for survival, such as cetaceans: restricted to water, immobile, their helpless young would drown. In birds, the terms Aves altrices and Aves precoces was introduced by Carl Jakob Sundevall and the terms nidifugous and nidicolous by Lorenz Oken in 1816.
The two classifications were considered identical in early times, but the meanings are different, in that "altricial" and "precocial" refer to developmental stage, while "nidifugous" and "nidicolous" refer to leaving or staying at the nest. The two strategies result in different brain sizes of the newborns compared to adults. Precocial animals' brains are large at birth relative to their body size, hence their ability to fend for themselves. However, as adults, their brains are not more able. Altricial animals' brains are small at birth, thus their need for care and protection, but their brains continue to grow; as adults, altricial animals end up with comparatively larger brains than their precocial counterparts. Thus the altricial species have a wider skill set at maturity. Precocial Parental investment The altricial-precocial spectrum in birds