shark sharks group fish characterized skeleton seven gill slits sides head pectoral fins fused head modern sharks classified clade sister group rays term shark extinct members outside broader definition earliest known sharks date million years ago referred sharks proper leading fish sharks species range size small dwarf deep sea species centimetres length whale shark largest fish world reaches approximately metres length sharks found seas common depths metres generally live freshwater known exceptions bull shark river shark survive found freshwater sharks covering dermal denticles protects skin damage parasites addition improving fluid dynamics numerous sets teeth known species great white shark tiger shark blue shark shark shark apex predators organisms underwater food chain shark populations threatened human activities etymology 16th century sharks known sea dogs etymology word shark uncertain largely theory derives maya word pronounced evidence etymology came oxford english dictionary notes shark came use sir sailors exhibited london posted refer large sharks caribbean_sea records isolated occurrence word shark referring sea fish letter written rules etymology etymology states original sense word predator dutch meaning villain card shark loan shark etc later applied fish predatory behaviour evolution evidence existence sharks dates period million years ago land existed plants continents scales recovered sharks agree true sharks scales actually oldest generally accepted shark scales million years ago period sharks looked different modern sharks majority modern sharks traced million years ago fossils teeth large numbers partial skeletons complete remains discovered estimates suggest sharks grow tens thousands teeth lifetime explains abundant fossils teeth consist easily calcium shark dies skeleton breaks scattering preservation requires rapid burial sediments ancient primitive sharks million years ago found strata ohio kentucky tennessee point earth history rocks soft sediments large shallow ocean stretched north_america metre long stiff triangular fins slender jaws teeth pointed wore use small number teeth found likely replace teeth regularly modern sharks caudal fins similar shape great white sharks presence fish arranged tail suggest fast swimmers great agility fossil sharks million years ago assigned groups exclusive freshwater environments time group extinct million years ago spread worldwide group appeared million years ago lived oceans freshwater results study gill structure unusually preserved million year old fossil suggested sharks living fossils evolved extensively previously thought hundreds millions years modern sharks began appear million years ago fossil shark teeth date early cretaceous recently evolved families shark family emerged oldest white shark teeth date million years ago time extinction early white shark evolution lineage white sharks teeth probably gave rise modern great white shark lineage white sharks finely teeth sharks attained gigantic proportions include extinct shark like extinct sharks primarily known fossil teeth giant shark reached total length metres approached metres total length metric tons short tons mass evidence suggests shark active predator large taxonomy sharks belong class include rays include currently thought sharks form group sharks closely related rays sharks divided usually placed clade recent studies clade scientists think divided includes contains invalid includes invalid includes species sharks split thirteen orders including orders sharks gone extinct commonly known ground sharks order includes blue tiger bull grey reef reef caribbean reef reef reef oceanic sharks collectively called requiem sharks sharks distinguished elongated snout membrane protects eyes attack generally referred horn sharks examples group include cow sharks sharks somewhat resembles marine snake commonly known sharks include shark shark shark sharks sharks great white shark distinguished large jaws reproduction include extinct commonly referred carpet sharks including sharks nurse sharks whale shark elongated toothed snout use prey group includes sharks known angel sharks flattened sharks strong resemblance anatomy teeth shark teeth embedded directly jaw constantly replaced life multiple rows replacement teeth grow groove inside jaw steadily forward comparison belt sharks lose teeth lifetime rate tooth replacement varies days months species teeth replaced time opposed simultaneous replacement entire row observed shark tooth shape depends shark diet feed crustaceans dense flattened teeth crushing feed fish needle like teeth gripping feed larger prey mammals pointed lower teeth gripping triangular upper teeth edges cutting teeth shark small non functional skeleton shark skeletons different bony fish terrestrial sharks fish rays skeletons tissue flexible half normal density bone reduces skeleton weight saving energy sharks rib easily crushed weight land jaw jaws sharks like rays attached jaw surface comparison shark gill arches needs extra support heavy exposure physical stress need strength layer tiny plates called crystal blocks calcium arranged mosaic gives areas strength found bony tissue found animals generally sharks layer jaws large specimens bull shark tiger shark great white shark layers depending body size jaws large great white shark layers snout flexible absorb power impacts fins fin skeletons elongated supported soft rays named elastic protein resembling hair feathers sharks fins sharks drift away objects directly fins allow tail direction dermal denticles unlike bony fish sharks complex dermal flexible fibers arranged network surrounding body works outer skeleton providing attachment swimming muscles saving energy dermal teeth advantages reduce swimming tails tails provide thrust making speed acceleration dependent tail shape caudal fin shapes vary considerably shark species evolution separate environments sharks possess caudal fin dorsal portion usually noticeably larger ventral portion shark column extends dorsal portion providing greater surface area muscle attachment allows efficient negatively fish contrast bony fish possess caudal fin tiger sharks large upper lobe allows slow cruising sudden bursts speed tiger shark able twist turn water easily hunting support varied diet shark hunts schooling fish herring large lower lobe help pace fast swimming prey tail adaptations help sharks catch prey directly shark usage powerful elongated upper lobe fish squid physiology unlike bony fish sharks gas filled swim instead sharks rely large liver filled oil contains half normal density bone liver constitutes total body mass liver effectiveness limited sharks employ dynamic lift maintain depth swimming sand tiger sharks store air form swim dwelling sharks like nurse shark negative allowing rest ocean floor sharks inverted nose enter natural state researchers use condition handle sharks safely like fish sharks extract oxygen passes gills unlike fish shark gill slits covered lie row head modified called lies eye assists shark taking water plays major role dwelling sharks reduced missing active sharks shark moving water passes mouth gills process known ram ventilation rest sharks pump water gills ensure constant supply water small number species lost ability pump water gills swim rest species ram presumably unable ram ventilation true bony fish species circulation process begins blood travels shark heart shark pumps blood gills ventral branches takes place gills blood flows come form dorsal blood flows dorsal body blood body flows posterior cardinal veins enters posterior cardinal blood enters heart cycle repeats sharks cold precisely meaning internal body temperature matches ambient environment members family shark great white shark maintain higher body temperature surrounding water sharks strip red muscle located near center body generates heat body retains exchange mechanism system blood vessels called net common shark similar mechanism maintaining elevated body temperature thought evolved independently contrast bony fish exception blood tissue sharks generally marine environments high concentration allowing balance adaptation prevents sharks surviving freshwater confined marine environments exceptions exist bull shark developed way change kidney function large amounts shark dies broken bacteria causing dead body gradually smell strongly long time food moves mouth shaped stomach stored initial occurs unwanted items past stomach instead shark turns inside unwanted items mouth biggest differences digestive systems sharks mammals sharks shorter short length achieved spiral valve multiple turns single short section instead long tube like valve provides long surface area requiring food inside short gut fully remaining waste products pass senses smell sharks keen senses located short fused unlike bony fish anterior posterior nasal openings species able detect little million blood sharks ability determine direction given scent based timing scent detection similar method mammals use determine direction sound attracted chemicals found species result near sewage species nurse sharks external greatly increase ability sense prey sight shark eyes similar eyes including similar lenses adapted marine environment help tissue called tissue reflects light increasing visibility dark waters effectiveness tissue varies sharks having stronger nocturnal adaptations sharks contract pupils like humans fish sharks surrounding water eyes protect eyes species membranes membrane covers eyes hunting shark attacked species including great white shark membrane instead roll eyes backwards protect striking prey importance sight shark hunting behavior debated believe significant point membrane evidence sight important presumably shark protect eyes use sight probably varies species water conditions shark field vision swap time micro study species shark found rod cone cells giving good night vision making remaining seven species addition rods single type cone sensitive green seeing shades grey green believed effectively study indicates object contrast background colour important object detection hearing hard test hearing sharks sharp sense hearing possibly hear prey miles away small opening heads leads directly inner ear thin channel lateral line shows similar arrangement open environment series openings called lateral line pores reminder common origin sound detecting organs grouped system bony fish external opening inner ear lost organs number hundreds thousands sharks use detect electromagnetic fields living things produce helps sharks particularly shark find prey shark greatest electrical sensitivity animal sharks find prey hidden sand detecting electric fields produce ocean currents moving magnetic field earth generate electric fields sharks use orientation possibly navigation lateral line system found fish including sharks motion vibrations water shark sense frequencies range life history shark vary species live years longest lifespan years whale sharks live years reproduction unlike bony fish sharks selected meaning produce small number developed young opposed large number poorly developed young sharks ranges young reproductive cycle sharks mature slowly relative fish example lemon sharks reach sexual maturity age sexual sharks practice internal posterior male shark pelvic fins modified pair organs called analogous deliver sperm female mating rarely observed sharks smaller mate male female flexible species sharks swim parallel male female females larger species bite marks appear result male maintain position mating bite marks come courtship behavior male bite female interest species females evolved thicker skin withstand bites number documented cases female shark contact male conceived details process understood genetic showed pups paternal genetic contribution ruling sperm storage extent behavior wild unknown species capability mammals major group reproduction observed scientists reproduction wild rare probably ditch effort reproduce mate present reproduction genetic diversity helps build defenses threats species species rely solely risk extinction reproduction contributed blue shark decline irish coast brooding sharks display ways bear young varying species sharks meaning eggs hatch mother body egg yolk walls embryos young continue remnants yolk young born alive fully functional sharks practice embryos hatch eat remaining eggs taking step sand tiger shark pups consume neighboring embryos survival strategy species brood young comparatively large size birth whale shark classified eggs thought aborted sharks birth sheltered areas including bays river mouths shallow reefs choose areas protection predators mainly sharks abundance food longest known gestation period shark months sharks sharks appear longer gestation periods accurate data lacking species like fish laying eggs water shark species egg case consistency leather protects developing embryo cases protection egg case known purse wash shore sharks include horn shark shark finally sharks maintain link developing young method called analogous gestation fishes young born alive fully functional requiem sharks bull blue sharks viviparous behavior classic view describes solitary hunter ranging oceans search food applies species live far social benthic lives appear likely distinct personalities solitary sharks meet breeding rich hunting grounds lead cover thousands miles year shark migration patterns complex birds sharks covering entire ocean basins sharks highly social remaining large schools islands cross species social exist example oceanic sharks dominate silky sharks comparable size feeding approached closely sharks perform threat display usually consists exaggerated swimming movements vary intensity according threat level speed general sharks swim cruise average speed kilometres hour mph feeding attacking average shark reach speeds upwards kilometres hour mph shark fastest shark fastest fish burst speeds kilometres hour mph great white shark capable speed bursts exceptions warm nature sharks physiology sharks travel day intelligence sharks possess brain body mass similar mammals birds exhibited apparent curiosity behavior resembling play wild evidence juvenile lemon sharks use learning investigation novel objects environment sleep sharks need water flowing gills order breathe species need moving able breathe swimming force water gills allowing extract oxygen water recorded eyes remain open state actively follow movements divers swimming truly asleep species need swim continuously breathe process known sleep swimming shark essentially unconscious known experiments conducted spinal cord brain coordinates swimming continue swim sleeping case larger shark species ecology feeding sharks sharks whale sharks sharks independently evolved different strategies filter feeding sharks practice ram feeding whale sharks use small fishes sharks feeding efficient tissue inside mouths attract prey deep ocean type feeding requires gill long slender form efficient analogous plates great shark traps time time huge teeth species comparatively small needed feeding highly specialized include sharks feed flesh larger fish marine mammals teeth enormous compared animal size lower teeth particularly sharp observed feeding believed prey use thick lips seal twisting bodies rip flesh dwelling species highly effective ambush predators angel sharks use camouflage lie wait suck prey mouths benthic sharks feed solely crustaceans crush flat teeth sharks feed squid fish swallow teeth point strike capture prey intact great white large predators swallow small prey huge bites large animals sharks use long tails fishes stir prey slash swimming prey tooth sharks including reef shark cooperative hunt packs herd capture elusive prey social sharks migratory traveling huge distances ocean basins large schools partly necessary find new food sources range habitat sharks found seas generally live fresh water exceptions bull shark river shark swim freshwater sharks common depths metres live deeper entirely absent metres deepest confirmed report shark portuguese metres relationship humans attacks undertook investigation alleged shark attacks confirming attacks provoked attacks average number fatalities worldwide year shark attacks contrary popular belief sharks dangerous humans species involved significant number fatal attacks humans great white oceanic tiger bull sharks sharks large powerful predators attack kill people despite responsible attacks humans filmed protective cage perception sharks dangerous animals popularized publicity given isolated attacks shark attacks popular fictional works shark attacks jaws film series jaws author jaws director steven_spielberg later attempted image sharks man eating monsters help avoid attack humans wear jewelry metal shiny refrain captivity recently benthic species shark leopard sharks survived conditions year gave rise belief sharks difficult capture transport difficult care knowledge led species including large sharks living far longer captivity safer transportation techniques enabled long distance transportation long time great white shark successfully held captivity long september successfully kept young female days releasing species suitable home species sold pet stores appropriate species flourish home dealers sell juvenile sharks like nurse shark reaching adulthood far large typical home public generally accept donated specimens housing owners tempted release species appropriate home represent considerable spatial financial investments generally approach adult lengths feet live years hawaii sharks figure prominently hawaiian mythology stories tell men shark jaws change shark human form common theme shark man warn beach sharks waters beach laugh ignore warnings eaten shark man warned hawaiian mythology includes shark gods fishing people popular ancestor guardians shark describes detail offer corpse shark body transforms gradually point awe struck family markings shark body correspond clothing beloved body wrapped shark family pet receiving food driving fish family net danger like evil uses helping kill enemies ruling chiefs typically forbade native hawaiian families claim known community best known revered shark gods older favored brother helped hawaii able assume human fish forms summit cliff crater sacred spots point temple shrine dedicated piece land ocean island ancestral god human shark banned eating humans eating shark god lost souls popular culture contrast complex portrayals european western view sharks historically fear sharks popular culture commonly eating machines notably jaws novel film sequels sharks threats films reef comedic effect series comedic effects seen batman movie channel films like sharks tend seen cartoons scene involves ocean examples include tom jerry cartoons shows produced commonly means killing character held rope similar object sharks swim right character standing shark infested waters popular popular myth sharks immune disease cancer scientifically supported sharks known cancer diseases parasites affect sharks evidence sharks resistant cancer disease scientific statistical studies sharks heightened immunity disease apparently false claims fins prevent cancer treat scientific proof supports claims study shown shark value cancer treatment conservation fishery estimated million sharks killed people year commercial recreational fishing shark yields estimated million metric tons million tons based analysis average shark weights translates total annual mortality estimate million sharks million sharks total range possible values million sharks year sharks common places including japan australia australian state victoria shark commonly fish fish chips battered deep fried fish chip shops shark called india small sharks baby sharks called tamil language telugu language sold local markets flesh developed cooking flesh breaks powder fried oil called soft bones easily considered coastal greenland sharks produce widely regarded national dish year period estimated million sharks killed traded annually commercial markets sharks killed shark fin soup fishermen capture live sharks fin dump animal water shark involves removing fin hot metal blade resulting shark soon dies predators shark fin major trade black markets world fins sell illegally fin millions year governments enforce laws protect hawaii state prohibit possession sale trade distribution shark fins estimated million sharks killed year harvesting shark fins shark fin soup status symbol asian countries considered healthy nutrients sharks killed meat european consume rays lists sharks fish king high mercury content hazardous children pregnant women sharks generally reach sexual maturity years produce offspring comparison harvested fish harvesting sharks reproduce severely impacts future populations majority shark fisheries little monitoring management rise demand shark products increases pressure fisheries major declines shark stocks recorded species depleted past years population declines unusual study suggests quarter known species sharks rays threatened extinction species classified critically endangered threats threats include habitat alteration damage loss coastal development pollution impact fisheries prey species documentary exposed sharks hunted extinction protection south_africa country world declare sharks legally protected species intending ban practice shark sea united_states congress passed years later act saw legal challenge united_states approximately pounds ruled law allowed non fishing vessels purchase shark fins fishing vessels high seas seeking close shark conservation act passed congress december signed law january european_union introduced general shark ban vessels union waters vessels flying flag member states prohibition amended june close remaining named species oceanic shark species risk extinction fishing shark cites rejected proposals united_states required countries strictly regulate trade species oceanic sharks majority required thirds voting delegates approved proposal china far world largest shark market japan battles attempts extend convention marine species led opposition march endangered commercially valuable sharks oceanic added appendix cites bringing shark fishing commerce species licensing regulation added school shark shark shark tiger shark red list list common supermarket fish sourced fisheries advocacy group campaigns limit shark fishing advocacy group directs american consumers eat sharks auspices convention conservation migratory species wild animals known memorandum understanding concluded came effect march global instrument concluded aims international coordination protection conservation management migratory sharks discussion scientific research july new_york state major market entry point shark fins banned shark fin trade joining seven states united_states pacific territories providing legal protection sharks
Shark