biology of sharks and their relatives pdf

Biology Of Sharks And Their Relatives Pdf

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Sharks and their relatives : ecology and conservation

Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton , five to seven gill slits on the sides of the head , and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha or Selachii and are the sister group to the rays.

However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus , as well as other Chondrichthyes such as the holocephalid eugenedontidans. Under this broader definition, the earliest known sharks date back to more than million years ago. Since then, sharks have diversified into over species. They range in size from the small dwarf lanternshark Etmopterus perryi , a deep sea species of only 17 centimetres 6.

They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark , which can be found in both seawater and freshwater. They have numerous sets of replaceable teeth. Well-known species such as the tiger shark , blue shark , great white shark , mako shark , thresher shark , and hammerhead shark are apex predators —organisms at the top of their underwater food chain.

Many shark populations are threatened by human activities. Until the 16th century, [8] sharks were known to mariners as "sea dogs". The etymology of the word "shark" is uncertain, the most likely etymology states that the original sense of the word was that of "predator, one who preys on others" from the Dutch schurk , meaning "villain, scoundrel" cf.

A now disproven [ original research? However, the Middle English Dictionary records an isolated occurrence of the word shark referring to a sea fish in a letter written by Thomas Beckington in , which rules out a New World etymology. Evidence for the existence of sharks dates from the Ordovician period, — million years ago, before land vertebrates existed and before a variety of plants had colonized the continents. The majority of modern sharks can be traced back to around million years ago.

Partial skeletons and even complete fossilized remains have been discovered. Estimates suggest that sharks grow tens of thousands of teeth over a lifetime, which explains the abundant fossils. The teeth consist of easily fossilized calcium phosphate , an apatite. When a shark dies, the decomposing skeleton breaks up, scattering the apatite prisms.

Preservation requires rapid burial in bottom sediments. Among the most ancient and primitive sharks is Cladoselache , from about million years ago, [14] which has been found within Paleozoic strata in Ohio, Kentucky, and Tennessee.

At that point in Earth's history these rocks made up the soft bottom sediments of a large, shallow ocean, which stretched across much of North America. Cladoselache was only about 1 metre 3. From the small number of teeth found together, it is most likely that Cladoselache did not replace its teeth as regularly as modern sharks. Its caudal fins had a similar shape to the great white sharks and the pelagic shortfin and longfin makos.

The presence of whole fish arranged tail-first in their stomachs suggest that they were fast swimmers with great agility. Most fossil sharks from about to million years ago can be assigned to one of two groups. The Xenacanthida was almost exclusive to freshwater environments.

The other group, the hybodonts , appeared about million years ago and lived mostly in the oceans, but also in freshwater. Modern sharks began to appear about million years ago. One of the most recently evolved families is the hammerhead shark family Sphyrnidae , which emerged in the Eocene. In early white shark evolution there are at least two lineages: one lineage is of white sharks with coarsely serrated teeth and it probably gave rise to the modern great white shark, and another lineage is of white sharks with finely serrated teeth.

These sharks attained gigantic proportions and include the extinct megatoothed shark, C. Like most extinct sharks, C. Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates ; the Chondrichthyes also include Chimaeras.

It was thought that the sharks form a polyphyletic group: some sharks are more closely related to rays than they are to some other sharks, [23] but current molecular studies support monophyly of both groups of sharks and batoids. Lamnoids and Carcharhinoids are usually placed in one clade , but recent studies show the Lamnoids and Orectoloboids are a clade.

Some scientists now think that Heterodontoids may be Squalean. The Squaleans are divided into Hexanchiformes and Squalomorpha. The former includes cow shark and frilled shark , though some authors propose both families to be moved to separate orders. The Squalomorpha contains the Squaliformes and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the Squatiniformes , and the Pristorajea, which may also be invalid, but includes the Pristiophoriformes and the Batoidea.

There are more than species of sharks split across twelve orders , including four orders of sharks that have gone extinct: [26]. Shark teeth are embedded in the gums rather than directly affixed to the jaw, and are constantly replaced throughout life.

Multiple rows of replacement teeth grow in a groove on the inside of the jaw and steadily move forward in comparison to a conveyor belt ; some sharks lose 30, or more teeth in their lifetime.

The rate of tooth replacement varies from once every 8 to 10 days to several months. In most species, teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row, which is observed in the cookiecutter shark.

Tooth shape depends on the shark's diet: those that feed on mollusks and crustaceans have dense and flattened teeth used for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as mammals have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting.

The teeth of plankton-feeders such as the basking shark are small and non-functional. Shark skeletons are very different from those of bony fish and terrestrial vertebrates.

Sharks and other cartilaginous fish skates and rays have skeletons made of cartilage and connective tissue. Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton's weight, saving energy. The jaws of sharks, like those of rays and skates, are not attached to the cranium.

The jaw's surface in comparison to the shark's vertebrae and gill arches needs extra support due to its heavy exposure to physical stress and its need for strength. It has a layer of tiny hexagonal plates called " tesserae ", which are crystal blocks of calcium salts arranged as a mosaic. Generally sharks have only one layer of tesserae, but the jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have two to three layers or more, depending on body size.

The jaws of a large great white shark may have up to five layers. Fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling the horny keratin in hair and feathers. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction.

Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body.

This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy. Tails provide thrust, making speed and acceleration dependent on tail shape. Caudal fin shapes vary considerably between shark species, due to their evolution in separate environments.

Sharks possess a heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is because the shark's vertebral column extends into that dorsal portion, providing a greater surface area for muscle attachment.

This allows more efficient locomotion among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a homocercal caudal fin. Tiger sharks have a large upper lobe , which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the porbeagle shark , which hunts schooling fish such as mackerel and herring , has a large lower lobe to help it keep pace with its fast-swimming prey.

Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver filled with oil that contains squalene , and their cartilage, which is about half the normal density of bone. Sand tiger sharks store air in their stomachs, using it as a form of swim bladder.

Bottom-dwelling sharks, like the nurse shark , have negative buoyancy, allowing them to rest on the ocean floor. Some sharks, if inverted or stroked on the nose, enter a natural state of tonic immobility. Researchers use this condition to handle sharks safely. Like other fish, sharks extract oxygen from seawater as it passes over their gills. Unlike other fish, shark gill slits are not covered, but lie in a row behind the head. A modified slit called a spiracle lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom—dwelling sharks.

Spiracles are reduced or missing in active pelagic sharks. While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species. The respiration and circulation process begins when deoxygenated blood travels to the shark's two-chambered heart.

Here the shark pumps blood to its gills via the ventral aorta artery where it branches into afferent brachial arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the posterior cardinal veins and enters the posterior cardinal sinuses.

From there blood enters the heart ventricle and the cycle repeats. Most sharks are "cold-blooded" or, more precisely, poikilothermic , meaning that their internal body temperature matches that of their ambient environment. Members of the family Lamnidae such as the shortfin mako shark and the great white shark are homeothermic and maintain a higher body temperature than the surrounding water. In these sharks, a strip of aerobic red muscle located near the center of the body generates the heat, which the body retains via a countercurrent exchange mechanism by a system of blood vessels called the rete mirabile "miraculous net".

The common thresher and bigeye thresher sharks have a similar mechanism for maintaining an elevated body temperature. In contrast to bony fish, with the exception of the coelacanth , [43] the blood and other tissue of sharks and Chondrichthyes is generally isotonic to their marine environments because of the high concentration of urea up to 2.

This adaptation prevents most sharks from surviving in freshwater, and they are therefore confined to marine environments.

Discovery of a new mode of oviparous reproduction in sharks and its evolutionary implications

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Carrier and J. Musick and M. Carrier , J.

Biology of Sharks and Their Relatives (Marine Biology)

This module will examine the evolutionary history, taxonomic diversity and ecology of sharks and their relatives. Particular consideration will be given to shark population ecology, physiology and feeding, movement patterns, and human impacts to shark populations and attempts to mitigate these impacts. Current research relating to various anthropogenic impacts and conservation issues such as by-catch, shark finning, pollution and habitat destruction will also be presented and discussed. Evolutionary history of sharks The differences between sharks and some of their relatives e. The students should be able to express a basic factual knowledge of at least some part of the core material presented in the module, and be able to show some level of appreciate how the ecology of elasmobranchs and oceanographic drivers combine to help explain distributions and migrations.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Two modes of oviparity are known in cartilaginous fishes, 1 single oviparity where one egg case is retained in an oviduct for a short period and then deposited, quickly followed by another egg case, and 2 multiple oviparity where multiple egg cases are retained in an oviduct for a substantial period and deposited later when the embryo has developed to a large size in each case.

Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton , five to seven gill slits on the sides of the head , and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha or Selachii and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus , as well as other Chondrichthyes such as the holocephalid eugenedontidans. Under this broader definition, the earliest known sharks date back to more than million years ago.

Extinction risk and conservation of the world’s sharks and rays

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A nursery Area for Sharks and Rays in Northeastern Brazil

The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1, chondrichthyan fishes—sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing targeted and incidental. Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe.

Теперь предстояло принять решение. Бросить все и ехать в аэропорт. Вопрос национальной безопасности. Он тихо выругался. Тогда почему они послали не профессионального агента, а университетского преподавателя.

 - Мы уходим или нет? - Его руки клещами сжимали горло Сьюзан. Стратмор знал, что, если он сейчас достанет мобильник и позвонит в службу безопасности, Сьюзан будет жить. Он готов был спорить на что угодно, хоть на собственную жизнь, потому что ясно представлял себе весь сценарий. Этот звонок будет для Хейла полной неожиданностью. Он запаникует и в конце концов, столкнувшись с группой вооруженных людей, ничего не сможет поделать. После минутного упорства ему придется уступить.


PDF | On Feb 1, , Keiichi Sato published Biology of sharks and their relatives, second edition | Find, read and cite all the research you.


Kutipan duplikat

Как ты легко можешь себе представить, я был шокирован, впервые наткнувшись на его письмо Северной Дакоте о не поддающемся взлому коде, именуемом Цифровая крепость. Я полагал, что это невозможно. Но всякий раз, когда я перехватывал очередное сообщение, Танкадо был все более и более убедительным. Когда я прочитал, что он использовал линейную мутацию для создания переломного ключа, я понял, что он далеко ушел от нас. Он использовал подход, который никому из нас не приходил в голову.

Хейл сдавил горло Сьюзан немного сильнее, и она вскрикнула от боли. - Ну что, вы решили. Я ее убиваю. Стратмор мгновенно взвесил все варианты. Если он позволит Хейлу вывести Сьюзан из шифровалки и уехать, у него не будет никаких гарантий. Они уедут, потом остановятся где-нибудь в лесу.

 Прочитаешь за дверью. А теперь выходи. Но Мидж эта ситуация явно доставляла удовольствие. Она подошла к окну, вертя бумагу перед глазами, чтобы найти лучший угол для падения лунного света. - Мидж… пошли. Это личный кабинет директора. - Это где-то здесь, - пробормотала она, вглядываясь в текст.

Копия, которую он разместил, зашифрована. Ее можно скачать, но нельзя открыть. Очень хитро придумано. Ключ к Цифровой крепости зашифрован и недоступен. - Ну разумеется! - Она только сейчас поняла смысл сказанного.

Скрытые тенью, на него смотрели глаза Грега Хейла, глаза, полные ужаса. Тогда Стратмор понял, что Грег Хейл должен умереть. В ТРАНСТЕКСТЕ послышался треск, и Стратмор приступил к решению стоявшей перед ним задачи - вырубить электричество.

Хаос, царивший в комнате оперативного управления, воспринимался ею как отдаленный гул. Люди на подиуме не отрываясь смотрели на экран. Агент Смит начал доклад. - По вашему приказу, директор, - говорил он, - мы провели в Севилье два дня, выслеживая мистера Энсея Танкадо.

4 comments

Fulxencio B.

Biology of Sharks and Their Relatives,. Second Edition-Jeffrey C. Carrier ​ Virtually every area of research associated with sharks and their relatives​.

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Olaf G.

Download this publication.

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Rabican J.

Elasmobranch nurseries are habitats where females give birth to their young and juveniles spend their early life history.

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Shellidelarosa

Request PDF | On Jan 1, , Jeffrey C. Carrier published Biology of Sharks and Their Relatives | Find, read and cite all the research you need on.

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