What Percent Of The Animal Kingdom Do Vertebrates Makeup Hagfishes

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sea turtle (reptile). Green turtle (Chelonia mydas) (C. mydas) off the Hawaii Islands, Pacific Islands. Green sea turtle, chelonian. Homepage blog 2011, science and technology, animal — © iStockphoto/Thinkstock

How many of you call up the Brady Bunch episode in which Peter was studying for a biological science test? He asked Marcia for aid, and she taught him the mnemonic: "A vertebrate has a back that'south directly." Well, not all vertebrates have straight backs, but all take backbones, or vertebral columns, that help support their bodies.

Although the vertebral column is peradventure the most obvious characteristic in vertebrates, it was non present in the first ones, which probably had only a notochord (flexible rodlike structure which plays a role in the development of the nervous system). The vertebrate has a distinct head, with a differentiated encephalon and three pairs of sense organs (nasal, optic, and otic [hearing]). The body is divided into trunk and tail regions.

Several groups of vertebrates inhabit planet Earth. Let'southward accept a bout of the five main vertebrate groups alive today: the fishes, amphibians, reptiles, birds, and mammals.

Fishes

whale shark
A whale shark (Rhincodon typus) and a snorkeler off the coast of Australia.
© Comstock Images/Jupiterimages

The first fishes are thought to take emerged some 518 million years ago during the Cambrian Flow of World's history. Today, there more than xxx,000 species of fishes found in the fresh and common salt waters of the world. Living species range from the archaic, jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes.

Fishes range in adult length from less than 10 mm (0.iv inch) to more 20 meters (lx anxiety) and in weight from about 1.five grams (less than 0.06 ounce) to many thousands of kilograms. Some alive in shallow thermal springs at temperatures slightly in a higher place 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than than four,000 meters (13,100 feet) beneath the bounding main surface.

Fish reproduction methods vary, but nearly fishes lay a big number of small eggs that are fertilized and scattered outside of the body. The eggs of pelagic (open ocean) fishes usually remain suspended in the open water, while many shore and freshwater fishes lay eggs on the bottom or amongst plants. The bloodshed of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Amphibians

red salamander (Pseudotriton ruber)
Red salamanders (Pseudotriton ruber) are constitute in the eastern U.s..
© Liz Weber/Shutterstock.com

Amphibians evolved from fully aquatic tetrapods—(which were essentially "limbed fish") who descended from lobe-finned fish—old between the Early on Devonian Flow (which began 419 million years ago) to the Early Pennsylvanian Subperiod (which began 323 million years ago). The name amphibian, derived from the Greek amphibious meaning "living a double life," reflects this dual life strategy—though some species are permanent state dwellers, while other species take a completely aquatic way of being.

There are three living groups of amphibians (caecilians, salamanders, and anurans [frogs and toads]) that, collectively, make up more than 7,300 amphibian species. One similar tendency amid amphibians has been the development of straight evolution, in which the aquatic egg and free-swimming larval stages are eliminated. Development occurs fully within the egg capsule, and juveniles hatch as miniatures of the adult body form. Almost species of lungless salamanders (family Plethodontidae), the largest salamander family, some caecilians, and many species of anurans accept straight development. In improver, numerous caecilians and a few species of anurans and salamanders requite birth to alive young.

Frogs and toads brandish a wide variety of life histories. Some deposit eggs on vegetation higher up streams or ponds; upon hatching, the tadpoles drop into the water where they continue to develop throughout their larval phase. Some species create foam nests for their eggs in aquatic (watery), terrestrial (land-based), or arboreal (tree-based) habitats; after hatching, tadpoles usually develop in water. Other species eolith their eggs on country and send them to water, while marsupial frogs are so called because they behave their eggs in a pouch on their backs. A few species lack a pouch and the tadpoles are exposed on the dorsum; in some species, the female person deposits her tadpoles in a pond as soon as they sally from eggs.
Reptiles

male flying lizardPremaphotos/Nature Film Library

Reptiles are air-breathing vertebrates. They have internal fertilization, amniotic development (in which the embryo develops within a set of protective extra-embryonic membranes—the amnion, chorion, and allantois), and epidermal scales covering function or all of their body. The major groups of living reptiles—the turtles, tuataras, lizards and snakes, and crocodiles account for over 8,700 species.
Reptiles evolved from amphibians during the first part of the Pennsylvanian subperiod (323 million to 299 million years ago) and retained many amphibian structural characteristics. While almost reptiles feed on other organisms, a few are herbivorous (e.thou., tortoises). Every bit cold-blooded animals, reptiles tend to be limited to temperate and tropical areas, simply, where they occur, they are relatively common; however, they are non as big or conspicuous as birds and mammals. Most reptiles are terrestrial, but a few are aquatic. They move well-nigh by creeping or swimming in a fashion similar to amphibians. Some reptiles, all the same, can lift the body from the ground and run rapidly either in a quadrupedal or bipedal fashion. Reptiles lay relatively big, shelled eggs. In a few instances, the eggs and immature are cared for by the female; in others, the young are born alive.
Birds

European white pelican
European white pelicans (Pelecanus onocrotalus) in flight.
© Digital Vision/Getty Images

Birds make upwardly whatever of the 9,600 living species unique in having feathers, the major characteristic that distinguishes them from all other animals. They are warm-blooded vertebrates more related to reptiles than to mammals. They take a four-chambered heart (equally do mammals), forelimbs modified into wings (a trait shared with bats), a hard-shelled egg, and keen vision. Their sense of smell is not highly developed, and their auditory range is limited.

Although nearly are capable of flight, others are sedentary, and some are flightless. In a manner similar to their relatively close relatives the reptiles, birds lay shelled eggs. The young are usually cared for in a nest until they are capable of flying and self-feeding, just some birds hatch in a well-developed state that allows them to begin feeding immediately or fifty-fifty take flight. (Nesting activities similar to those of some birds are seen in the crocodilians.)

The origin of birds, feathers, and avian flying have long been hotly debated; the development of birds from reptilian ancestors is universally accepted, notwithstanding. The diversity of theropod dinosaurs (a diverse group of cannibal "cadger-hipped" dinosaurs), some with feathers, has greatly expanded our perspective of the development and early diversification of birds. While it is known that the critical period in avian evolution and flying took place during the Early Cretaceous (145.5 million to 99.vi meg years ago), at that place is evidence that feathers on theropods emerged much earlier, possibly during the Triassic and Jurassic Periods (some 252 one thousand thousand to 145 1000000 years ago).
Mammals

Okapi (Okapia johnstoni).
© IMPALASTOCK/iStock/Getty Images Plus

In that location are approximately 5,000 species of mammals living today. Mammals differ from other vertebrate animals in that their immature are nourished with milk from special mammary glands of the female parent. Mammals are distinguished past several other unique features. Pilus is a typical mammalian characteristic, although in many whales it has disappeared except in the fetal phase. The mammalian lower jaw is hinged directly to the skull, instead of through a separate bone (the quadrate) as in all other vertebrates. A chain of three tiny bones transmits sound waves across the middle ear. A muscular diaphragm separates the middle and the lungs from the intestinal cavity. Mature red blood cells (erythrocytes) in all mammals lack a nucleus; all other vertebrates have nucleated carmine blood cells. The oldest known animals classified equally mammals evolved near the boundary of the Triassic and Jurassic Periods, some 200 million years ago.

This grouping of vertebrates ranges in size from tiny shrews or small bats weighing only a few grams to the largest known animals, the whales. Most mammals are terrestrial, feeding on both animate being and vegetable matter, just a few are partially aquatic or entirely so, as in the case of the whales or porpoises. Mammals move about in a slap-up variety of ways: burrowing, bipedal or tetrapedal (four-legged) running, flying, or swimming. Reproduction usually involves the young developing inside the uterus, where nutritive materials are fabricated bachelor through an allantoic placenta or, in a few cases, a yolk sac. In placental mammals, young accept a longer developmental menses within the uterus. In marsupials, the relatively undeveloped young are carried in a pouch, where they attach themselves to their mother's nipple until they get fully developed. Monotreme mammals (that is, the platypus and echidna) differ from other mammals in that they lay eggs which hatch.