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Dorsal Fin

Dorsal fin

A dorsal fin is a fin located on the backs of fishes, whales, dolphins and porpoises, as well as the (extinct) ichthyosaurs. Its main purpose is to stabilise the animal against rolling and assist in sudden turns. Some animals have developed dorsal fins with protective functions, such as spines or venom. Many catfish can lock the leading ray of the dorsal fin in an extended position to discourage predation or to wedge themselves into a crevice. Dorsal fins come in a variety of shapes and sizes.

Fish

Nearly all types of fish have at least one dorsal fin, although there are some exceptions, such as the knifefish. Many have two or even three fins, or the fin may be a long one that merges with the caudal fin (tail). A very common pattern, characteristic of the many familiar species in the order Perciformes, is to have an forward dorsal fin formed from sharp spines, and a rear dorsal of soft rays. See fish anatomy for more details.

Whales, dolphins and porpoises

In relation to the size of the creature, the dorsal fin of the male orca is quite large, as much as 1.8 m high. Many (30-100%) captive killer whales (orcas) experience collapse of the dorsal fin, possibly because lack of exercise through turning leads to diminished muscle tone. (Only about 1% of wild orcas have collapsed dorsal fins.) The dorsal fins of most other whales are relatively small. The bowhead whale has no dorsal fin at all, as an evolutionary adaptation to its life spent cruising under icepack. The dorsal fins of whales develop distinctive nicks and wear patterns with time, and this fact is used by wildlife biologists to identify individuals in the field. Category:Anatomy ja:背びれ

Fish

Conodonta
Hyperoartia
:Petromyzontidae (lampreys)
Pteraspidomorphi (early jawless fish)
Thelodonti
Anaspida
Cephalaspidomorphi (early jawless fish)
:Galeaspida
:Pituriaspida
:Osteostraci
Gnathostomata (jawed vertebrates)
:Placodermi
:Chondrichthyes (cartilaginous fish)
:Acanthodii
:Osteichthyes (bony fish)
::Actinopterygii (ray-finned fish)
::Sarcopterygii (lobe-finned fish)
:::Actinistia (coelacanths)
:::Dipnoi (lungfish)
A fish is a poikilothermic (cold-blooded) water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates. Taxonomically, fish are a paraphyletic group whose exact relationships are much debated; a common division is into the jawless fish (class Agnatha, 75 species including lampreys and hagfish), the cartilaginous fish (class Chondrichthyes, 800 species including sharks and rays), with the remainder classed as bony fish (class Osteichthyes). Fish come in different sizes, from the 14m (45 ft) whale shark to a 7 mm (just over 1/4 of an inch) long stout infantfish. Many types of aquatic animals named "fish", such as jellyfish and cuttlefish, are not true fish. Other sea dwelling creatures, like dolphins, are actually mammals. Certain species of fish maintain elevated body temperatures to varying degrees. Endothermic teleosts (bony fishes) are all in the suborder Scombroidei and include the billfishes, tunas, and one species of "primitive" mackerel (Gasterochisma melampus). All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are known to have the capacity for endothermy, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. See also gigantothermy. Endothermy, though metabolically costly, is thought to provide advantages such as increased contractile force of muscles, higher rates of central nervous system processing, and higher rates of digestion.

Fish ecology

Fish can be found in almost all large bodies of water in either salt, brackish, or fresh water, at depths ranging from just below the surface to several thousand meters. However, hyper-saline lakes like the Great Salt Lake do not support fishes. Some species of fish have been specially bred to be kept and displayed in an aquarium, and can survive in the home environment. Catching fish for the purpose of food or sport is known as fishing. The annual yield from all fisheries worldwide is about 100 million tonnes. Overfishing is a threat to many species of fish. On May 15 2003, the journal Nature reported that all large oceanic fish species worldwide had been so systematically over caught that fewer than 10% of 1950 levels remained. [http://www.globeandmail.com/servlet/story/RTGAM.20030514.wfish1405/BNStory/National/] Particularly imperiled were sharks, Atlantic cod, Bluefin tuna, and Pacific sardines. The authors recommended immediate, drastic cutbacks in fish catches and reservation of ocean habitats worldwide.

Note on usage: "fish" vs. "fishes"

"Fishes" is the proper English plural form of "fish" that biologists use when speaking about two or more fish species, as in "There are over 25,000 fishes in the world" (meaning that there are over 25,000 fish species in the world). When speaking of two or more individual fish organisms, then the word "fish" is used, as in "There are several million fish of the species Gadus morhua" (meaning that G. morhua comprises several million individuals). To see both in action, consider the statement "There are twelve fish in this aquarium, representing five fishes" (meaning that the aquarium contains twelve individuals, some of the same species and some of different species, for a total of five species). The usage of the two words is similar to that of the words "people" and "peoples".

Fish as food

Fishes are an important source of food in many cultures. Other water-dwelling animals such as mollusks, crustaceans, and shellfish are often called "fish" when used as food. For more details, see Fish (food). Fish (food)

External links

- [http://www.70south.com/resources/animals/marine/antarcticfish 70South - information on Antarctic fish]
- [http://www.aworldoffish.com A World of Fish] Species information and fish care
- [http://www.fishbase.org Fish database] (FishBase)
- Join Ray Mullet in the [http://www.liverpoolmuseums.org.uk/nof/fish/ Fish Olympics]!
- Project for children - [http://marine.rutgers.edu/~kils/BASS/mobile/INDEX.HTM build a fish mobile with a behavior]
- [http://www.aquatichouse.com Fish Keeping]
- [http://www.aquaticcommunity.com Site with one of the largest fish databases in the world]
- [http://reelinthefish.net/interviews/jameskoliver.html Reelinthefish.net | Interview with Dr James K. Oliver, Reefbase Scientist]
- [http://fishy.us Fishy.Us]Articles & Particles
- [http://hardrockforums.com/forums Saltwater & Freshwater Forums]
- [http://www.fishfriend.com/ Your Fish Tank's Friend]
- [http://find-a-seafood-recipe.com/ Fish and Seafood Recipes]Cooking With Fish
- [http://www.easyreefer.com/ Reef aquarium community and learning center]
- [http://www.fiberi.de German Educator in Fisheries, Specialist in Fancy Goldfish and Fishhealth, with Forum and large Picture-Gallery]
- [http://www.freeonlinegames.com/play/3019.html]Interesting fish game.
- [http://www.sushifaq.com The Sushi FAQ - (the alt.food.sushi Usenet group FAQ) at SushiFAQ.com]
- [http://sushiotaku.blogspot.com/ The Sushi Otaku Blog] Category:Fisheries science Category:Seafood zh-min-nan:Hî ko:물고기 ms:Ikan ja:魚類 simple:Fish th:ปลา

Dolphin

See article below. Dolphins are aquatic mammals related to whales and porpoises. The name is from Ancient Greek delphis meaning "with a womb", viz. "a 'fish' with a womb". The word is used in a few different ways. It can mean: #Any member of the family Delphinidae (oceanic dolphins), #Any member of the families Delphinidae and Platanistoidea (oceanic and river dolphins), #Any member of the suborder Odontoceti (toothed whales; these include the above families and some others), #Used casually as a synonym for Bottlenose Dolphin, the most common and familiar species of dolphin. In this article, the second definition is used. Porpoises (suborder Odontoceti, family Phocoenidae) are thus not dolphins in our sense. Orcas and some related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common language. There are almost 40 species of dolphin in 17 genera. They vary in size from 1.2 m (4 ft) and 40 kg (88 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and 10 tonnes (the Orca). Most species weigh about 50 to 200 kg (110 to 440 lb). They are found worldwide, mostly in the shallower seas of the continental shelves, and all are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about 10 million years ago, during the Miocene.

Taxonomy

- Suborder Odontoceti, toothed whales
- Family Delphinidae, oceanic Dolphins
- Genus Delphinus
- Long-Beaked Common Dolphin, Delphinus capensis
- Short-Beaked Common Dolphin, Delphinus delphis
- Genus Tursiops
- Bottlenose Dolphin, Tursiops truncatus
- Genus Lissodelphis
- Northern Rightwhale Dolphin, Lissodelphis borealis
- Southern Rightwhale Dolphin, Lissiodelphis peronii
- Genus Sotalia
- Tucuxi, Sotalia fluviatilis
- Genus Sousa
- Indo-Pacific Hump-backed Dolphin, Sousa chinensis
-
- Chinese White Dolphin, the Chinese variant
- Atlantic Humpbacked Dolphin, Sousa teuszii
- Genus Stenella
- Atlantic Spotted Dolphin, Stenella frontalis
- Clymene Dolphin, Stenella clymene
- Pantropical Spotted Dolphin, Stenella attenuata
- Spinner Dolphin, Stenella longirostris
- Striped Dolphin, Stenella coeruleoalba
- Genus Steno
- Rough-Toothed Dolphin, Steno bredanensis
- Genus Cephalorynchus
- Chilean Dolphin, Cephalorhynchus eutropia
- Commerson's Dolphin, Cephalorhynchus commersonii
- Heaviside's Dolphin, Cephalorhynchus heavisidii
- Hector's Dolphin, Cephalorhynchus hectori
- Genus Grampus
- Risso's Dolphin, Grampus griseus
- Genus Lagenodelphis
- Fraser's Dolphin, Lagenodelphis hosei
- Genus Lagenorhyncus
- Atlantic White-Sided Dolphin, Lagenorhynchus acutus
- Dusky Dolphin, Lagenorhynchus obscurus
- Hourglass Dolphin, Lagenorhynchus cruciger
- Pacific White-Sided Dolphin, Lagenorhynchus obliquidens
- Peale's Dolphin, Lagenorhynchus australis
- White-Beaked Dolphin, Lagenorhynchus albirostris
- Genus Orcaella
- Australian Snubfin Dolphin, Orcaella heinsohni
- Irrawaddy Dolphin, Orcaella brevirostris
- Genus Peponocephalia
- Melon-headed Whale, Peponocephalia electra
- Genus Orcinus
- Killer Whale, Orcinus orca
- Genus Feresa
- Pygmy Killer Whale, Feresa attenuata
- Genus Pseudorca
- False Killer Whale, Pseudorca crassidens
- Genus Globicephala
- Long-finned Pilot Whale, Globicephala melas
- Short-finned Pilot Whale, Globicephala macrorhynchus
- Family Platanistoidea, River Dolphins
- Genus Inia
- Boto (Amazon River Dolphin), Inia geoffrensis
- Genus Lipotes
- Chinese River Dolphin (Baiji), Lipotes vexillife
- Genus Platanista
- Ganges River Dolphin, Platanista gangetica
- Indus River Dolphin, Platanista minor
- Genus Pontoporia
- La Plata Dolphin (Franciscana), Pontoporia blainvillei Six animals in the family Delphinidae are commonly called "whales" but are strictly speaking dolphins. They are sometimes called "blackfish":
- Melon-headed Whale, Peponocephalia electra
- Killer Whale, Orcinus orca
- Pygmy Killer Whale, Feresa attenuata
- False Killer Whale, Psudoorca crassidens
- Long-finned Pilot Whale, Globicephala melas
- Short-finned Pilot Whale, Globicephala macrorhynchus

Hybrid Dolphins

In 1933, three strange dolphins were beached off the Irish coast; these appeared to be hybrids between Risso's Dolphin and the Bottlenose Dolphin. This mating has since been repeated in captivity and a hybrid calf was born. In captivity, a Bottlenose Dolphin and a Rough-Toothed Dolphin produced hybrid offspring. In the wild, Spinner Dolphins have sometimes hybridised with Spotted Dolphins and Bottlenose Dolphins. In the wild, bands of males of one dolphin species have been observed to mate with lone female Spinners. Blue Whales, Fin Whales and Humpback Whales all hybridize in the wild. Dall's Porpoises and Harbour Porpoises have hybridized in the wild. There has also been a reported hybrid between a beluga and a narwhal. See also wolphin.

Evolution and anatomy of dolphins

Dolphins, along with whales and porpoises, are descendants of land-living mammals, most likely of the Artiodactyl order. Modern dolphin skeletons have two small rod shaped pelvic bones thought to be left-over hind legs. They entered the water roughly 50 million years ago. See evolution of cetaceans for the details. Dolphins have a fusiform body, adapted for fast swimming. The head contains the melon, a round organ used for echolocation. In many species, the jaws are elongated, forming a distinct beak; for some species like the Bottlenose, there is a curved mouth that looks like a fixed smile. Teeth can be very numerous (up to 250) in several species. The dolphin brain is large and has a highly structured cortex, which often is referred to in discussions about their high intelligence. The basic coloration patterns are shades of gray with a light underside and a distinct dark cape on the back. It is often combined with lines and patches of different hue and contrast. See individual species articles for details.

Dolphin behavior

dolphin brain Dolphins are widely believed to be amongst the most intelligent of all animals. A typical statement would be that dolphins are roughly as intelligent as a two-year-old human. However, experts in comparative psychology or animal cognition would be reluctant to make any such estimate, as quantitative comparisons of intelligence between species are notoriously difficult to make in principle. Straightforward comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition; furthermore, the difficulty and expense of doing experimental work with a large marine animal mean that even such tests as can meaningfully be done have still not been done, or have been carried out with inadequate sample size and methodology. See the Dolphin intelligence article for more details. Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g. the spinner dolphin). This and other behavior is interpreted as playing. They are capable of diving up to 260 m deep and 15 min long, but rarely stay underwater longer than few minutes. Frequently dolphins will accompany boats, riding the bow waves. They are also famous for their willingness to occasionally approach humans and playfully interact with them in the water. In return, in some cultures like in Ancient Greece they were treated with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. There have been reports of dolphins protecting swimmers against sharks by swimming circles around the swimmers. Dolphins are social animals, living in pods (also called "schools") of up to a dozen animals. In places with a high abundance of food, schools can join temporarily, forming an aggregation called a superpod; such groupings may exceed 1000 dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. echolocation Membership in schools is not rigid; interchange is common. However, the animals can establish strong bonds between each other. This leads to them staying with injured or ill fellows for support. Because of their high capacity for learning, humans have employed dolphins for any number of purposes. Dolphins trained to perform in front of an audience have become a favorite attraction in dolphinaria, for example SeaWorld. Dolphin/Human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled children. The military has employed dolphins for various purposes from finding mines to rescuing lost or trapped persons. Such military dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that dolphins were being trained to kill Vietnamese Skin Divers. In May 2005, researchers in Australia discovered a cultural aspect of dolphin behaviour: Some dolphins (Tursiops aduncus) teach their offspring to use a tool. The animals break off sponges and put them onto their mouths thus protecting the delicate body part during their hunt for fish on the seabed. Other than with primate simians, the knowledge to use a tool is mostly handed over only from mothers to daughters. The technology to use sponges as mouth protection is not genetically inherited but a taught cultural behaviour. Dolphins do not have acute eyesight nor do they appear to have a good sense of smell, although their sense of hearing is far above our own. Compare also: whale behavior

Feeding

Dolphins are predators, chasing their prey at high speed. The dentition is adapted to the animals they hunt: Species with long beaks and many teeth forage on fish, whereas short beaks and lesser tooth count are linked to catching squid. Some dolphins may take crustaceans. Usually, the prey is swallowed whole. The bigger species, especially the orca, are capable of eating marine mammals, even large whales. There are no known reports of cannibalism amongst dolphins. Individual species may employ a number of methods of hunting:
- Herding - where a superpod will control a school of fish while individual members take turns plowing through the herd, feeding.
- Corralling - where fish are chased to shallow water where they are more easily captured.
- Fish Wacking - where the dolphin uses its fluke to strike the fish, stunning it and sometimes sending it clear out of the water.
- Stunning - using the echolocation melon, very loud clicks are directed at prey, stunning them.
- Foraging - A recent study reported that wild bottlenose dolphins (Tursiops sp.) in Western Australia use sponges to forage in the sea bed for food.[http://www.pnas.org/cgi/content/abstract/0500232102v1]

Dolphin lore

- The popular television show Flipper, created by Ivan Tors, portrayed a dolphin in a friendly relationship with two boys, Sandy and Bud; a kind of sea going Lassie, Flipper understood English unusually well and was a marked hero: "Go tell Dad we're in trouble, Flipper! Hurry!" The show's theme song contains the lyric no one you see / is smarter than he.
- In The Hitchhiker's Guide to the Galaxy, dolphins are very intelligent creatures who tried in vain to warn humans of the impending destruction of Earth. However, their behavior was misinterpreted as playful acrobatics. Their story is told in So Long, and Thanks for All the Fish.
- After study at the Dolphins Plus research center in Key Largo, Florida, fantasy author Ken Grimwood wrote dolphins into his 1995 novel Into the Deep, including entire chapters written from the viewpoint of his dolphin characters.
- Ecco The Dolphin stars in a series of games for the Sega Genesis/Mega Drive, Game Gear, Sega Dreamcast and Playstation 2.
- A book called 'The Music of Dolphins' was written by Karen Hesse, about a girl who had lived with dolphins since the age of four.
- An American National Football League (NFL) team is named the Miami Dolphins. Their logo depicts an aqua-colored bottlenose dolphin wearing an American football helmet and jumping in front of a coral-colored sunburst.
- The Mystery Science Theater 3000 episode Devil Fish, features Mike and the 'Bots mocking dolphins. While doing so, the SOL gets blasted by a ship that turns out to be piloted by dolphins. Mike and the 'Bots then quickly apoligize.

External links

- [http://news.bbc.co.uk/2/hi/asia-pacific/4034383.stm Dolphins help lifeguards from sharks]
- [http://www.cetacea.org/ Cetacea.org site]
- [http://www.robins-island.org/ Facts and Information on Dolphins]
- [http://www.hickerphoto.com/dolphin-pictures-cat.htm Dolphin Pictures]
- [http://www.robertosozzani.it/Delfini/cont.html Red Sea Spinner Dolphin - Photo gallery]
- [http://www.tursiops.org/ Tursiops.org: Current Dolphin-related news]
- [http://www.wilddolphin.org/dolphinpictures.htm Wild Dolphin Foundation; Hawaiian Spinner Dolphin pictures, videos, information and conservation]
- [http://www.pbs.org/wnet/nature/dolphins/index.html PBS NOVA: Dolphins: Close Encounters]
- [http://www.accobams.org/download/articles/population/Agazzi_etal_2004.pdf Common dolphin prey species in the eastern Ionian Sea]
- [http://www.whale-images.com/facts_about_dolphins.htm facts about dolphins]
- [http://www.omplace.com/omsites/discover/DOLPHINS/ OM Place] A pictorial comparitive chart. Category:Cetaceans ko:돌고래 ja:イルカ simple:Dolphin

Ichthyosaur

Cymbospondylus
Mixosauridae
Merriamosauria
Shastasauridae/Shastasauria
Euichthyosauria
Parvipelvia
Leptonectidae
Thunnosauria
Stenopterygidae
Ichthyosauridae Ichthyosaurs (Greek for "fish lizards") were giant marine reptiles that resemble a dolphin with large teeth (see convergent evolution). They lived during a large part of the Mesozoic era, and appeared about 250 million years ago (Ma), slightly earlier than the dinosaurs (230 Ma); and disappeared about 90 Ma, about 25 million years before the dinosaurs became extinct. During the early Triassic, ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water, in a development similar to dolphins' and whales'. They were particularly abundant in the Jurassic period, until they were replaced as the top aquatic predators by plesiosaurs in the Cretaceous. They belong to the order known as Ichthyosauria or Ichthyopterygia ("fish flippers" a designation introduced by Sir Richard Owen in 1840, although the term is now used more for the parent clade of the Ichthyosauria).

Description

Ichthyosaurs averaged 2 to 4 meters in length (although a few were smaller, and some species grew much larger), with a porpoise-like head and a long, toothed snout. They had a large tail fin and their limbs were adapted for use as steering paddles. They were carnivorous, coming to the surface to fill their lungs with air and viviparous, for fossils have been found with their fossilized fetal young. Viviparity should not be as surprising as it appears at first: air-breathing marine creatures must come ashore to lay eggs, like turtles and some sea snakes, or else give birth to live young in surface waters. Built for speed, like modern tuna, ichthyosaurs also apparently were deep divers, like some modern whales (Motani, 2000). It has been estimated that ichthyosaurs could swim at speeds up to 25 mph (40 km/h). According to weight estimates by Ryosuke Motani [http://www.ucmp.berkeley.edu/people/motani/ichthyo/weight.html] a 2.4 meter (8 ft) Stenopterygius weighed around 163 to 168 kg (360 to 370 lb), whilst a 4.0 meter (13 ft) Ophthalmosaurus icenicus weighed 930 to 950 kg (about a ton). Although ichthyosaurs looked like fish they were not. Biologist Stephen Jay Gould said the ichthyosaur was his favorite example of convergent evolution, where similarities of structure are analogous not homologous, for this group: :"converged so strongly on fishes that it actually evolved a dorsal fin and tail in just the right place and with just the right hydrological design. These structures are all the more remarkable because they evolved from nothing— the ancestral terrestrial reptile had no hump on its back or blade on its tail to serve as a precursor." dorsal fin In fact the earliest reconstructions of ichthyosaurs omitted the dorsal fin, which had no hard skeletal structure, until finely-preserved specimens recovered in the 1890s from the Holzmaden lagerstätten in Germany revealed traces of the fin. For their food, many of the fish-shaped ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites. Some early ichthyosaurs had teeth adapted for crushing shellfish. They also most likely fed on fish, and a few of the larger species had heavy jaws and teeth that indicated they fed on smaller reptiles. Ichthyosaurs ranged so widely in size, and survived for so long, that they are likely to have had a wide range of prey. Typical ichthyosaurs have very large eyes, protected within a bony ring, suggesting they may have hunted at night.

History of discoveries

The first fossil vertebrae were published twice in 1708 as tangible mementos of the Universal Deluge. The first complete ichthyosaur fossil was found in 1811 by Mary Anning in Lyme Regis, along what is now called the Jurassic Coast. In 1905, the Saurian Expedition led by John C. Merriam of the University of California and financed by Annie Alexander, found 25 specimens in central Nevada, which during the Triassic was under a shallow ocean. Several of the specimens are now in the collection of the University of California Museum of Paleontology. Other specimens are embedded in the rock and visible at Berlin-Ichthyosaur State Park in Nye County. In 1977 the Triassic ichthyosaur Shonisaurus is the State Fossil of Nevada. Nevada is the only state to possess a complete skeleton, 55 ft (17 m) of this extinct marine reptile.

Evolutionary history

The earliest ichthyosaurs, looking more like finned lizards than the familiar fish or dolphin forms, are known from the Early and Early-Middle (Olenekian and Anisian) Triassic strata of Canada, China, Japan, and Spitsbergen in Norway. These primitive forms included the genera Chaohusaurus, Grippia, and Utatsusaurus. These very early proto-ichthyosaurs, which are now classified as Ichthyopterygia rather than as ichthyosaurs proper (Motani 1997, Motani et al. 1998), quickly gave rise to true ichthyosaurs sometime in the latest Early Triassic or earliest Middle Triassic. These latter diversified into a variety of forms, including the sea-serpant like Cymbiospondylus, which reached 10 meters, and smaller more typical forms like Mixosaurus. By the Late Triassic, ichthyosaurs consisted of both classic Shastasauria and more advanced, "dolphin"-like Euichthyosauria (Californosaurus, Toretocnemus) and Parvipelvia (Hudsonelpidia, Macgowania). Experts disagree over whether these represent an evolutionary continum, with the less specialised shastosaurs a paraphyletic grade that was evolving into the more advanced forms (Maisch and Matzke 2000), or whether the two were separate clades that evolved from a common ancestor earlier on (Nicholls and Manabe 2001). During the Carnian and Norian, shastosaurs reached huge sizes. Shonisaurus popularis, known from a number of specimens from the Carnian of Nevada, was 15 meters long. Norian shonisaurs are known from both sides of the Pacific. Himalayasaurus tibetensis and Tibetosaurus (probably a synonym) have been found in Tibet. These large (10 to 15 meters long) ichthyosaurs probably belong to the same genus as Shonisaurus (Motani et al, 1999; Lucas, 2001, pp.117-119). While the gigantic Shonisaurus sikanniensis, whose remains were found in the Pardonet formation of British Columbia by Elizabeth Nicholls, reached as much as 23 meters in length - the largest marine reptile known to date. These giants (along with their smaller cousins) seemed to have disappeared at the end of the Norian. Rhaetian (latest Triassic) ichthyosaurs are known from England, and these are very similar to those of the Early Jurassic. Like the dinosaurs, the ichthyosaurs and their contemporaries the plesiosaurs survived the end-Triassic extinction event, and immediately diversified to fill the vacant ecological niches of the earliest Jurassic. The Early Jurassic, like the Late Triassic, was the heyday of the ichthyosaurs, which are represented by four families and a variety of species, ranging from one to ten meters in length. Genera include Eurhinosaurus, Ichthyosaurus, Leptonectes, Stenopterygius, and the large predator Temnodontosaurus, along with the persistantly primitive Suevoleviathan, which was little changed from its Norian ancestors. All these animals were streamlined, dolphin-like forms, although the more primitive animals were perhaps more elongated than the advanced and compact Stenopterygius and Ichthyosaurus. Ichthyosaurs were still common in the Middle Jurassic, but had now decreased in diversity. All belonged to the single clade Ophthalmosauria. Represented by the 4 meter long Ophthalmosaurus and related genera, they were very similar to Ichthyosaurus, and had attained a perfect "tear-drop" streamlined form. The eyes of Ophthalmosaurus were huge, and it is likely that these animals hunted in dim and deep water (Motani 2000). Ichthyosaurs seemed to decrease in diversity even further with the Cretaceous. Only a single genus is known, Platypterygius, and although it had a worldwide distribution, there was little diversity species-wise. This last ichthyosaur genus fell victim to the mid-Cretaceous (Cenomanian-Turonian) extinction event (as did some of the giant Pliosaurs), although ironically less hydrodynamically efficient animals like Mosasaurs and long-necked Plesiosaurs flourished. It seems that the ichthyosaurs became the victim of their own overspecialisation, and were unable to keep up with the fast swimming and highly evasive new teleost fishes that were becoming dominant at this time, and against which the sit and wait ambush strategies of the mosasaurs proved superior (Lingham-Soliar 1999).

References

- Ellis, Richard, (2003) Sea Dragons - Predators of the Prehistoric Oceans. University Press of Kansas ISBN 0-7006-1269-6
- Stephen Jay Gould, "Bent out of Shape" in Eight Little Piggies.
- Lingham-Soliar, T. (1999): A functional analysis of the skull of Goronyosaurus nigeriensis (Squamata: Mosasauridae) and Its Bearing on the Predatory Behavior and Evolution of the Enigmatic Taxon. N. Jb. Geol. Palaeont. Abh. 2134 (3): 355-74
- Maisch, M. W. & Matzke, A. T. (2000) The ichthyosauria. Stuttgarter Beitraege zur Naturkunde. Serie B. Geologie und Palaeontologie. 2000; (298): 1-159.
- McGowan, Christopher (1992) Dinosaurs, Spitfires and Sea Dragons, Harvard University Press, ISBN 067420770X
- Motani, R. (1997), Temporal and spatial distribution of tooth implantation in ichthyosaurs, in JM Callaway & EL Nicholls (eds.), Ancient Marine Reptiles. Academic Press. pp. 81-103.
- Motani, R. (2000), Rulers of the Jurassic Seas, Scientific American vol.283, no. 6
- Motani, R., Minoura, N. & Ando, T. (1998), Ichthyosaurian relationships illuminated by new primitive skeletons from Japan. Nature 393: 255-257.
- Motani, R., Manabe, M., and Dong, Z-M, (1999) The status of Himalayasaurus tibetensis (Ichthyopterygia) [http://www.uoregon.edu/~rmotani/pdf/sMotanietal1999a.pdf pdf], Paludicola2(2):174-181 June 1999
- Nicholls, E. L. & Manabe, M. 2001. A new genus of ichthyosaur from the Late Triassic Pardonet Formation of British Columbia: bridging the Triassic-Jurassic gap. Canadian Journal of Earth Sciences 38, 983-1002.

External links

- [http://www.ucmp.berkeley.edu/diapsids/ichthyosauria.html USMP Berkeley's ichthyosaur introduction]
- [http://www.ucmp.berkeley.edu/people/motani/ichthyo/ Ryosuke Motani's detailed Ichthyosaur homepage, with vivid graphics]
- [http://www.palaeos.com/Vertebrates/Units/210Eureptilia/300.html Eureptilia: Ichthyosauria - Palaeos]
- [http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Reptilia/Ichthyosauromorpha/Ichthyosauria.htm Ichthyosauria - cladogram] (Mikko's Phylogeny Archive) Category:Prehistoric reptiles

Caudal fin

fish anatomy#Fins

Fish anatomy

Fish anatomy is primarily governed by the physical characteristics of water, which is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs light more than does air.

Body

Nearly all fish have a streamlined body, which is divided into head, trunk, and tail, although the dividing points are not always externally visible. The head includes the snout, from the eye to the forwardmost point of the upper jaw, the operculum or gill cover, and the cheek, which extends from eye to preopercle. The lower jaw defines a chin. The head may have several fleshy structures known as barbels, which may be very long and resemble whiskers. Many fish species also have a variety of protrusions or spines on the head. The nostrils or nares of almost all fishes do not connect to the oral cavity, but are pits of varying shape and depth. The outer body of the fish is covered with scales.

Fins

The fins are the most distinctive features of a fish.
- The dorsal fin is located on the back.
- The caudal fin corresponds to the fish tail.
- The anal fin is located on the bottom, behind the anus.
- The pectoral fins are located on each side, usually at a middle height on the body just behind the head.
- The pelvic fins are on the belly.
- Some types of fish have a small fleshy adipose fin on the back just forward of the caudal fin.
- Some types of fish, notably certain sharks, have horizontal caudal keels just forward of the tail fin. They provide stability and support to the caudal fin. For every fin, there are a number of fish species in which this particular fin has disappeared during evolution.

Scales

There are four types of fish scales.
1. Placoid: these scales are "composed of body dentin covered by a layer of enamel." (Gilbertson, 7.4)
- Found in: only sharks
2. Ganoid: flat, basal-looking scales that cover a fish body without much overlapping.
- Found in: gar
3. Cycloid: Small oval-shaped scales with growth rings.
- Found in: bowfin, remora
4.Ctenoid: Similar to the Cycloid scales, with growth rings. Distinguishable by the spines that cover one edge.
- Found in: halibut Category:Ichthyology

Orca

The Orca (Orcinus orca), also known as the Killer Whale or Grampus, is the largest member of the oceanic dolphin family. It is the second-most widely distributed mammal on Earth (after humans) and is found in all the world's oceans. It is also a versatile predator, eating fish, turtles, birds, seals, sharks and even other juvenile and small cetaceans. This puts the Orca at the pinnacle of the marine food chain. The orca also attacks other whales, in particular Gray Whales. The name "killer whale" reflects the animal's reputation as a magnificent and fearsome sea mammal that goes as far back as Pliny the Elder's description of the species. Today it is recognized that the Orca is neither a whale (except in the broad sense that all cetaceans are whales) nor a danger to humans. No attack on a human by an Orca in the wild has ever been recorded. There have, however, been isolated reports of captive Orcas attacking their handlers at marine theme parks.
Naming
The name "Orca" (plural "Orcas") was originally given to these animals by the ancient Romans, possibly borrowed from the Greek word which (among other things) referred to a species of whale. The name "killer whale" is widely used in common English. However since the 1960s "orca" has steadily grown in popularity as the common name to identify the species and is now more popular than the traditional name amongst those in the field. There are several reasons for the change. First, having the word whale in the name of a species that is really a dolphin causes confusion. Second, the species is called orca in most other European languages and, as there has been a steady increase in the amount of international research on the species, there has been a convergence in naming. Furthermore, the killer in "killer whale" is often wrongly assumed to imply that the creature is a killer of humans, an attitude amplified by an unfortunate movie seeking to capitalize from the buzz from Jaws (1975). Orca: The Killer Whale (1977) starred Richard Harris and Bo Derek. It is thought this long standing and often fearful reputation can be put to rest by using the more neutral name of orca. A pod of Orcas is capable of taking down a large whale. It is commonly thought that 18th-century Spanish sailors dubbed these creatures asesina ballenas, or "whale killer" for this reason. However, this title was improperly translated into English as "killer whale". The term became so prevalent that Spanish speakers commonly used its retranslation of ballena asesina. This practice has further strengthened the case for using orca. There are still many who prefer the original name, believing it to be an appropriate description of a species that does indeed kill many animals, including other cetaceans. These supporters of the original name point out that the naming heritage is not limited to Spanish sailors. Indeed the genus name "Orcinus" means "from Hell" (see Orcus) and although the name "orca" (in use since antiquity) is probably not etymologically related, the assonance might have given some people the idea that it means "whale that brings death," or "demon from hell." It is noteworthy that the name of this species is similarly intimidating in many non-European languages. To the Haida people native to the islands of Haida Gwaii off the coast of British Columbia, the animal was known as skana or "killing demon". The Japanese call them shachi (鯱), whose kanji character combines the radicals for fish (魚) and tiger (虎).
Taxonomy and evolution
The Orca is the sole species in the genus Orcinus. It is one of thirty-five species in the dolphin family. Like the Sperm Whale genus Physeter, Orcinus is a genus with a single, abundant species with no immediate relatives from a cladistic point of view, thus palaeontologists believe that the Orca is a prime candidate to have an anagenetic evolutionary history — that is the evolution of ancestral to descendant species without splitting of the lineage. If true, this would make the Orca one of the oldest dolphin species, although it is unlikely to be as old as the family itself, which is known to date back at least five million years.
Physical characteristics
The animals are distinctively marked, with a black back, white chest and sides and a white patch above and behind the eye. They have a heavy and stocky body and a large dorsal fin with a dark gray "saddle patch" behind it. Males can be up to 9.5 m long (31 ft) and weigh in excess of 6 tons; females are smaller, reaching up to 8.5 m (28 ft) and a weight of about 5 tons. Calves at birth weigh about 180 kg and are about 2.4 m long (8 ft). Unlike most dolphins, the caudal fin of an Orca is large and rounded — more of a paddle than other dolphin species. At about 1.8 m (6 ft), the dorsal fin of the male is taller than the female's, and is more of a triangle shape — a tall, elongated isosceles triangle, whereas the dorsal fin of the female is shorter and shaped like a scythe. Nicks, cuts and scrapes on these fins, as well as distinctive features of each fin, help scientists identify individuals. Large male Orcas are very distinctive and are unlikely to be confused with any other sea creature. When seen from a distance in temperate waters, females and juveniles can be confused with various other species, such as the False Killer Whale or Risso's Dolphin. Most life history data about orcas has been obtained from long-term surveys of the population off the coasts of British Columbia and Washington and by monitoring captive whales. Due to the completeness of the study and highly structured nature of the pods in this population, the information is detailed and accurate; however, transient groups and groups in other oceans may have slightly different characteristics. Females become mature at around 15 years of age. From then they have periods of polyestrous cycling with non-cycling periods of between three and sixteen months. The gestation period varies from fifteen to eighteen months. Mothers calve, with a single offspring, about once every five years. In analysed resident pods, birth occurs at any time of year, with the most popular months being those in winter. New-born mortality is very high — one survey suggested that nearly half of all calves fail to reach the age of six months. Calves nurse for up to two years, but will start to take solid food at about twelve months. Cows breed until the age of 40, meaning that on average they raise five offspring. Typically females live to the age of fifty, but may survive well into their eighties or nineties in exceptional cases. Males become sexually active at the age of 15, and live to about 30 on average, and to 50 in exceptional cases.
Range
The orca is the second-most widely distributed mammal in the world, after the human. They are found in all oceans and most seas including (unusually for cetaceans) the Mediterranean and Arabian Seas. Cooler temperate and polar regions are preferred, however. Although sometimes spotted in deep water, coastal areas are generally preferred to pelagic environments. The Orca is particularly highly concentrated in the northeast Pacific Basin, where Canada curves into Alaska, off the coast of Iceland and off the coast of northern Norway. They are regularly sighted in Antarctic waters right up to the ice-pack and indeed are believed to venture under the pack and survive breathing in air pockets like the beluga does. In the Arctic, however, the species is rarely seen in winter, as it does not approach the ice pack. It does visit these waters during summer. Information for off-shore regions and tropical waters is more scarce but widespread, if not frequent; sightings indicate that the orca can survive in most water temperatures. No estimate for the total worldwide population exists. Local estimates include 70-80,000 in the Antarctic, 8,000 in the tropical Pacific (although tropical waters are not the orca's preferred environment, the sheer size of this area — 19 million square kilometres — means there are thousands of whales), up to 2,000 off Japan, 1,500 off the cooler northeast Pacific and 1,500 off Norway. Adding very rough estimates for unsurveyed areas, the total population could be around 100,000.
Social interaction
beluga Orcas have a complex system of social grouping. The basic unit is the matriline, which consists of a single female Orca (the matriarch) and her descendants. The sons and daughters of the matriarch form part of the line as do the sons and daughters of those daughters (the sons and daughters of the sons join the matriline of their mates) and so on down the family tree. Because females can live for up to ninety years, it is not uncommon for four or even five generations of Orcas living in the same line. These matrilineal groups are highly stable over many years. Individuals will only split off from their matrilineal group for up to a few hours at a time in order to mate or forage. No permanent casting out of an individual from a matriline has ever been recorded. The average matriline size as recorded in northeast Pacific waters is nine animals. Matrilines tend to congregate with a small number of other matrilines to form a pod, consisting on average of about 18 animals. Members of a pod all have the same dialect (see the song section below) and consist of closely related matriline fragments. Unlike matrilines, pods will split apart for days or weeks at a time in order to carry out foraging before joining back together. The largest recorded pod is 49 animals. The next level of grouping is the clan. A clan consists of those pods which have a similar dialect. Again the relationship between pods appears to be genealogical, consisting of fragments of families with a common heritage on the maternal side. Different clans can occupy the same geographical area; pods from different clans are often recorded traveling together. When resident pods come together to travel as a clan, they greet each other by forming two parallel lines akin to a face-off before mingling with each other. The final layer of association, perhaps more arbitrary and devised by humans rather than the other very natural divisions, is called the community and is loosely defined as the set of clans that are regularly seen mixing with each other. Communities do not follow discernible familial or vocal patterns. In the northeast Pacific there have been three communities identified: :
- The southern community (1 clan, 3 pods, 92 orcas as of 2005, counting Luna (L98)) :
- The northern community (3 clans, 16 pods, 214 orcas as of 2000) :
- The south Alaskan community (2 clans, 11 pods, 211 orcas as of 2000) It should be emphasized that these hierarchies are valid for resident groups only. Transient, mammal-eating groups are generally smaller because, although they too are based on matrilines, males are much more likely to split off to live a solitary life. However, transient groups still have a loose connection defined by their dialect. The day-to-day behaviour of Orcas is generally divided into four activities: foraging, traveling, resting and socializing. Orcas are generally enthusiastic in their socializing, exhibiting a wide range of breaching, spyhopping, tail-slapping and head-stands. All-male groups often interact with erect penises. Whether this interaction is part of play or a display of dominance is not known.
Diet
dominance]] There are 3 "types" of orcas studied off the North West American coast, residents, transients and offshores. Residents orcas only eat fish, transients eat seals, and other whales (other than orcas), and not enough is known about offshores to confirm their diet. The array of species on which Orcas prey is extremely diverse. Specific populations tend to specialize on particular prey species, even at the expense of ignoring other potential prey. For example, some populations in the Norwegian and Greenland sea specialise on herring and follow that fish's migratory path to the Norwegian coast each autumn. Other populations in the area prey on seals. Orcas are the only mammals with this diversification of feeding among overlapping species. The Orca is the only cetacean species to regularly prey on other cetaceans. Twenty-two species have been recorded as preyed on, either through an examination of stomach contents, examining scarring on the other cetacean's body, or by simply observing the feeding activity. Pods of Orcas will even prey upon larger whales such as Fin Whales, Minke Whales, Grey Whales, or even young Blue Whales. A group of Orcas take a young Blue Whale by chasing it and its mother through the sea, wearing them out. Eventually the orcas manage to separate the pair and then surround the younger whale, thereby preventing it from returning to the sea's surface in order to breathe. Once the whale has drowned, the orcas are free to feed on it. There has also been one recorded case of probable Orca cannibalism. A study carried out by V. I. Shevchenko in the temperate areas of the South Pacific in 1975 recorded two male Orca whose stomachs contained the remains of other Orcas. Of the 30 Orcas captured and examined in this survey, 11 had empty stomachs — an unusually high percentage that indicates the Orca were forced to cannibalism through a lack of food. More commonly, Orcas prey on 30 species of fish, particularly salmon (including chinook and coho), herring, and tuna. Basking sharks, oceanic whitetip sharks, and very occasionally even great white sharks are taken for their nutrient-rich livers. There is also believed to be an element of competition elimination in taking these sharks. Other marine mammals, including most species of seal and sea lion, are also taken by polar populations. Walrus and sea otters are taken less frequently. Seven species of bird are also taken, including all penguin species as well as sea birds such as cormorants. Cephalopods, such as octopuses and a wide range of squids, are also targets. Orcas are very inventive and playful in their killing. They sometimes will throw seals to one another through the air in order to stun and kill the animal. While salmon are usually hunted by a single orca or a small group of individuals, herring are often caught using carousel feeding: the orcas force the herring into a tight ball by releasing bursts of bubbles or flashing their white underside. The orcas then slap the ball with their tail flukes, either stunning or killing up to 10-15 herring with a successful slap. The herring are then eaten one at a time. Carousel feeding has only been documented in the Norwegian orca population and with some oceanic dolphin species. Sea lions are killed by head-butting or by being slapped and stunned by a tail fluke. An orca in Friendship Cove discovered that it could regurgitate fish onto the surface, attract sea gulls, and eat them. Other orcas then learned the behavior by example.[http://www.roanoke.com/theedge/wb/xp-32407] More specialized feeding techniques are used by various populations around the world. In Patagonia, orcas feed on southern sea lion and elephant seal pups by forcing them on to beaches, even to the extent of stranding themselves, albeit temporarily. Orcas will spy-hop to locate seals resting on ice floes, and then create a wave to wash over the floe, causing the seal to be thrown into the water where a second orca waits to kill it. On average, the orca eats 60 kg of food each day. With this huge variety of prey, and no predators other than man, the orca is very much at the top of the food chain.
Song
food chain As with other dolphins, orcas are very vocal animals. They produce a variety of clicks and whistles that are used for communication and echolocation. The vocalization types vary with activity. While resting, perhaps unsurprisingly, they are much quieter, merely emitting an occasional call that is distinct from those heard when engaging in more active behaviour. Resident pods of orcas tend to be much more vocal than transient groups. Scientists surmise that there are two main reasons for this. Firstly, resident orcas stay within the same social groups for much longer, thus developing more complicated social relationships resulting in greater vocalizations. Transient groups tend to stay together for much more fleeting amounts of time (usually just a period of hours or days) and thus communicate less. Secondly, transient orcas are much more likely to feed on marine mammals than fish-loving resident pods. Orcas hunting for mammals to eat naturally must be quieter to avoid the possibility of detection. For this reason, orcas that are hunting tend to use just a single click (called a cryptic click) for echolocation rather than the long train of clicks observed in other species. Resident pods have regional dialects. Each pod has its own songs or sets of particular whistles and clicks that it will repeat over and over. Every member of the pod seems to know all the songs of the pod, so it is not possible to identify a single animal using voice alone, only a dialectal group. A particular song might be known by only one group or shared among several. The degree to which two groups have their songs in common appears to be a function of their genealogical closeness rather than their geographical closeness. Two groups that share a common set of ancestors but have grown apart in distance are likely to have a similar set of songs. This suggests that songs are passed from mother to child during the nursing period. See also: Whale song
Orcas in history
Although only scientifically identified as species in 1758, the orca has been known to man since prehistoric times. The desert culture of Nazca created a Nazca line representing an orca sometime between 200 BC and AD 600. The first description of an orca is given in Pliny the Elder's Natural History (written circa 50 BC). The aura of invincibility around the all-consuming orca was well-established by this time. Having watched the public slaughtering of a whale stranded at a harbor near Rome, Pliny writes, "Orcas, (the appearance of which no image can express, other than an enormous mass of savage flesh with teeth), are the enemy of [other whales]... they charge and pierce them like warships ramming." Indigenous tribes in the Pacific Northwest of North America such as the Tlingit, Haida, and Tsimshian featured the orca prominently in their religion and artwork.
Orcas and modern man
religionn coast.]]
Hunting
Orcas were targeted in commercial whaling for the middle part of the twentieth century once stocks of larger species had been depleted. Commercial hunting of orcas came to an abrupt halt in 1981 with the introduction of the moratorium on all whaling. (Although from a taxonomic point of view an orca is a dolphin rather than a whale, it is sufficiently large to come under the purview of the International Whaling Commission.) The greatest hunter of orcas was Norway which took an average of 56 animals per year from 1938 to 1981. Japan took an average of 43 animals from 1946 to 1981. (War year figures are not available but are likely to be fewer). The Soviet Union took a few animals each year in the Antarctic, with the extraordinary exception of the 1980 season when it took 916. Today, no country carries out a substantial hunt. Japan usually takes a few individuals each year as part of its controversial program of "scientific research." A similarly small level of subsistence whaling is carried out by Indonesia and Greenland. As well as hunting for their meat, orcas have also been killed because of their competition with fishermen. In the 1950s the United States Air Force, at the request of the Government of Iceland, used bombers and riflemen to slaughter orcas in Icelandic waters because they competed with humans for fish. The operation was considered a great success at the time by fishermen and the Icelandic government. However, many were unconvinced that orcas were responsible for the drop in fish stocks, blaming overfishing by humans instead. This debate has led to repeated studies of North Atlantic fish stocks, with neither side in the whaling debate giving ground since that time. The orca is also occasionally killed out of fear of its reputation. No human has ever been attacked by an orca in the wild, but sailors in Alaska shoot the animal occasionally with concern for their own lives. This fear has generally dissipated in recent years due to better education about the species, including the appearance of orcas in aquariums and other aquatic attractions.
Captivity
The orca's intelligence, trainability, striking appearance, playfulness in captivity, and its sheer size have made it a popular exhibit at aquariums and other aquatic attractions such as aquatic theme parks. The first orca capture and display took place in Vancouver in 1964. Over the next 15 years around sixty or seventy orcas were taken from Pacific waters for this purpose. In the late 1970s and the first half of the 1980s, orcas were generally taken from Icelandic waters (fifty in the five years to 1985). Since that time, orcas have been successfully bred in captivity and wild specimens are considerably rarer. Orcas in captivity may develop pathologies such as dorsal fin collapse, seen in 60-90% of captive males. There have been incidents with orcas in captivity attacking humans. In 1991, a group of orcas killed a trainer named Keltie Byrne at Sealand in Victoria, British Columbia (where employees were not allowed in the water with orcas), apparently not knowing she could not survive underwater. In 1999, at the SeaWorld park in Orlando, Florida, one of the same orcas allegedly killed a tourist who had sneaked into the orca's pool at night[http://www.cnn.com/US/9907/06/killer.whale/]. (The dead tourist, who was otherwise physically unharmed, was also thought to be a victim of hypothermia.) In late July 2004, during a show at the SeaWorld park in San Antonio, Texas, an orca pushed its trainer of ten years underwater and barred the way to the rim of the pool; the trainer could only be rescued from the raging animal after several minutes. One of the more infamous incidents involving orca aggression took place in August 1989, when a dominant female whale, Kandu V, struck a newcomer whale, Corky II, with her mouth during a live show. Corky II had been imported from Marineworld California just months prior to the incident. According to reports, a loud smack was heard across the stadium. Although trainers tried to keep the show rolling, the blow severed an artery near Kandu V's jaw, and she began spouting blood. The crowd was quickly ushered out, and after a 45-minute hemorrhage, Kandu V died. Opponents of these shows see these incidents as supporting their criticism. SeaWorld continued to be implicated in unfair practices by keeping orcas taken from the wild, and came under criticism from the Born Free Foundation over its continued captivity of the orca Corky II, who they want to be returned to its family in the A5 Pod—a large pod of orcas in British Columbia, Canada [http://www.bornfree.org.uk/orca40.htm].
Popular culture
As late as the 1970s, orcas were depicted negatively in fiction as ravenous predators whose behavior caused heroes to interfere to help a prey animal escape. The most extreme example is the poorly received film Orca (an obvious attempt to duplicate the success of Jaws) which featured the story of a male orca going on a vengeful rampage after its pregnant mate is killed by humans. However, the increased research of the animal and its popularity in public venues brought about a dramatic rehabilitation of the animal's public image. The sentiment about the animal grew to more as a respected predator that poses little actual threat to humans, much as the North American wolf's image has been changed. The movie Free Willy (1993) focused on the quest for freedom for a captive orca. The whale starring in the movie, Keiko, was originally caught in Icelandic waters. After rehabilitation at the Oregon Coast Aquarium in Newport, Oregon, he was later returned to the waters of the Nordic countries, his native habitat, but continued to be dependent on humans until he died of pneumonia in December 2003.
Environmental threats
The Exxon Valdez oil spill had a particularly adverse effect on the Alaskan orca population. One pod was caught in the spill; though the pod successfully swam to clear water, eleven members of the pod (about half) died in the following days and weeks. The spill had a longer-term effect in reducing the amount of available prey, such as salmon, and has thus been responsible for a local population decline. In December 2004, scientists at the North Gulf Oceanic Society said that the pod (called the AT1 pod) now only came to seven in number, having failed to reproduce at all since the spill. The population is expected to become completely extinct. [http://www.presstelegram.com/Stories/0,1413,204~23170~2584776,00.html Press Telegram report on the pod] Like other animals at the highest trophic levels of the food chain, the orca is particularly susceptible to poisoning via accumulation of Polychlorinated biphenyls (PCBs) in the body. A survey of animals off the Washington coast found that PCB levels in orcas were higher than those in harbour seals in Europe that have been sickened by the chemical. Samples from the blubber of orcas in the Norwegian Arctic show higher levels of PCBs, pesticides and brominated flame-retardants than in Polar bears. However, no direct evidence of sickness in orcas has been found. The most likely effect, if any, would be a reduced rate of reproduction. On November 15, 2005 the United States government listed the Puget Sound Orca as an endangered species due to deterioration of the three pods which spend most of the year in Puget Sound in Washington State. Other environmental pressures facing orcas include extensive whale-watching which some research indicates changes whale behavior. Heavy ship noise has caused some groups of orca to change the frequencies of their songs and calls.
Famous Orca

- Shamu — performs along with Baby Shamu and Grandbaby Shamu at SeaWorld
- Keiko — performed in the first of the three Free Willy movies.
Media

References

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- (The author describes his discovery of orca cannibalism; in Russian, transliterations vary).
Other resources

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External links

- [http://www.orca-tysfjord.no Killer Whale safari, Tysfjord, Norway]
- [http://www.tysfjord.net/thumbnails.php?album=14 Killer whale images, Tysfjord, Norway]
- [http://www.70south.com/resources/animals/whales/killer 70South - information on the Killer Whale]
- [http://www.montereybaywhalewatch.com/Features/Photos0201/ Monterey Bay Whale Watch Photos: Killer Whales Attacking Gray Whales]
- [http://www.gowhales.com/Features/KillerWhalePredation0210.htm Predation Behavior of Transient Killer Whales in Monterey Bay, California]
- [http://www.orca-tysfjord.com Killer Whale image archive showing orca from Arctic Norway]
- [http://www.hickerphoto.com/killer-whale-pictures-cat.htm Killer Whale Pictures showing Offshore, Resident and Transient Killer Whales from Canada,BC]
- [http://www.killerwhale.no Research project studying Killer whales in the Norwegian Arctic]
- [http://www.whale-images.com/killer_whale_facts.htm Killer Whale facts]
- [http://www.shamu.com theme parks] featuring captive "killer whales"
- [http://www.orcaresearch.org New Zealand, Papua New Guinea and Antarctic orca research] Category:Cetaceans ja:シャチ

Bowhead Whale

The Bowhead Whale (Balaena mysticetus), also known as Greenland Right Whale or Arctic Whale, is a marine mammal of the order Cetacea.

Description

They are robust-bodied, dark-colored animals with no dorsal fin and a strongly bowed lower jaw and narrow upper jaw. The baleen plates of Bowhead Whales, which are used to strain tiny prey from the water, are the longest of any baleen whale, exceeding 3 meters. They have massively bony skulls which they use to break through the ice to breathe. Some Inuit hunters have reported whales surfacing through 2 feet (60 centimeters) of ice. Bowheads may reach lengths of up to 20 meters; females are larger than males. The blubber layer of the bowhead whale is thicker than in any other animal, averaging 43–50cm (17–20 in).

Distribution

Bowhead Whales are the only baleen whales that spend their entire lives in and around Arctic waters. The Bowhead Whales found off Alaska spend the winter months in the southwestern Bering Sea. They migrate northward in the spring, following openings in the pack ice, into the Chukchi and Beaufort seas, hunting krill and zooplankton. Bowheads are slow swimmers and usually travel alone or in small herds of up to six animals. Although they may stay below the water surface for as long as forty minutes in a single dive, they are not thought to be deep divers.

Reproduction and Lifespan

Bowhead Whales are highly vocal and use underwater sounds to communicate while traveling, feeding, and socializing. Some Bowheads produce long repetitive songs that may be mating displays. They also breach, tail slap, and spy-hop. Sexual activity occurs between pairs and in boisterous groups of several males and one or two females. Breeding has been observed from March through August; conception is believed to occur primarily in March. Reproduction can begin when a whale is 10 to 15 years old. Females produce a calf once every 3 to 4 years, after a 13- to 14-month pregnancy. The newborn calf is about 4.5 m long and approximately 1000 kg, growing to 9 m by its first birthday. The lifespan of a bowhead was once thought to be 60 to 70 years, similar to other whales. However, discoveries of antique ivory spear points in living whales in 1993, 1995 and 1999 have triggered further research based on structures in the whale's eye, leading to the reliable conclusion that at least some individuals have lived to be 150–200 years old (another report has said a female at the age of 90 was allegedly still reproductive). [http://www.gi.alaska.edu/ScienceForum/ASF15/1529.html Bowhead Whales May Be the World's Oldest Mammals]

Population Status

Bowhead Whales have been hunted for their blubber, meat, oil, bones and baleen. They are closely related to the right whale and share with it the hunting-friendly characteristics of slow swimming and floating after death. Before commercial whaling, there were over 50,000 Bowhead Whales in the north polar region (estimated). Commercial whaling starting in 1611 near Svalbard and Greenland and wiped out herds of the slow-growing whales, and then moved on to new areas. In the North Pacific, the commercial fishery began in the mid-1800s, and within two decades over 60 percent of the Bowhead Whale population had been killed. Commercial whaling, the principal cause of the population decline, has been discontinued. The stock off Alaska has increased since commercial whaling ceased. Alaskan natives continue to take small numbers of bowhead whales in subsistence hunts each year. This level of harvest (25–40 animals annually) is not expected to affect the stock's recovery. The Bowhead Whale population of Alaska's coast appears to be recovering but remains at about 7,800 animals (1990), roughly 41 percent of the pre-whaling population. The status of the other bowhead stocks is less well known. These stocks are thought to be very small, probably in the low hundreds, for a possible worldwide population of 8,000–9,200 individuals. The bowhead is one of the most seriously endangered of all the large whales, and is listed as such by CITES.

Range, behavior, and predators

The Bowhead spends all of its life in fertile Arctic waters, unlike other whales that migrate for feeding or reproduction. Bowheads are social and nonaggressive, and will retreat under the ice when threatened. Their predators are Orca and humans.

External links

- [http://nmml.afsc.noaa.gov/education/cetaceans/bowhead2.htm Bowhead Whale: Detailed Information from NOAA] Category:Cetaceans

Evolution

, based on rRNA gene data, showing the separation of the three domains, bacteria, archaea, and eukaryotes, as described initially by Carl Woese.]] In biology, evolution is the process by which populations of organisms acquire and pass on novel traits from generation to generation, affecting the overall makeup of the population and even leading to the emergence of new species. The terms organic evolution or biological evolution are often used to distinguish this meaning from other usages. The development of the modern theory of evolution began with the introduction of the concept of natural selection in a joint 1858 paper by Charles Darwin and Alfred Russel Wallace. This theory achieved a wider readership in Darwin's 1859 book, The Origin of Species. Darwin and Wallace proposed that evolution occurs because a heritable trait that increases an individual's chance of successfully reproducing will become more common, by inheritance, from one generation to the next, and likewise a heritable trait that decreases an individual's chance of reproducing will become rarer. This work was groundbreaking, and overturned other evolutionary theories, such as that advanced by Jean Baptiste Lamarck. Because of its potential implications for the origins of humankind, the theory has been at the center of many social and religious controversies since its first inception (see Creation-evolution controversy). In the 1930s, scientists combined Darwinian natural selection with the re-discovered theory of Mendelian heredity to create the modern synthesis, now one of the fundamental scientific theories of biology. In the modern synthesis, "evolution" is defined as a change in the frequency of alleles within a population from one generation to the next. The basic mechanisms that produce these changes are natural selection, genetic drift, and genetic variation. The primary sources of genetic variation are mutation, sex, and gene flow.

Overview of evolution

Evidence of evolution

The process of evolution has left behind numerous records which reveal the history of species. While the best-known of these are the fossils, fossils are only a small part of the overall physical record of evolution. Fossils, taken together with the comparative anatomy of present-day plants and animals, constitute the morphological record. By comparing the anatomies of both modern and extinct species, biologists can reconstruct the lineages of those species with some accuracy. Using fossil evidence, for instance, the connection between dinosaurs and birds has been established by way of so-called "transitional" species such as Archaeopteryx. The development of genetics has allowed biologists to study the genetic record of evolution as well. Although we cannot obtain the DNA sequences of most extinct species, the degree of similarity and difference among modern species allows geneticists to reconstruct lineages with greater accuracy. It is from genetic comparisons that claims such as the 98-99% similarity between humans and chimpanzees come from, for instance. Other evidence used to demonstrate evolutionary lineages includes the geographical distribution of species. For instance, monotremes and most marsupials are found only in Australia, showing that their common ancestor with placental mammals lived before the submerging of the ancient land bridge between Australia and Asia. Scientists correlate all of the above evidence – drawn from paleontology, anatomy, genetics, and geography – with other information about the history of the earth. For instance, paleoclimatology attests to periodic ice ages during which the climate was much cooler; and these are found to match up with the spread of species such as the woolly mammoth which are better-equipped to deal with cold.

Morphological evidence

Fossils are important for estimating when various lineages developed. As fossilization on an organism is an uncommon occurrence, usually requiring hard parts (like bone) and death near a site where sediments are being deposited, the fossil record only provides sparse and intermittent information about the evolution of life. Fossil evidence of organisms without hard body parts, such as shell, bone, and teeth, is sparse but exists in the form of ancient microfossils and the fossilization of ancient burrows and a few soft-bodied organisms. Fossil evidence of prehistoric organisms has been found all over the Earth. The age of fossils can often be deduced from the geologic context in which they are found; and their absolute age can be verified with radiometric dating. Some fossils bear a resemblance to organisms alive today, while others are radically different. Fossils have been used to determine at what time a lineage developed, and transitional fossils can be used to demonstrate continuity between two different lineages. Paleontologists investigate evolution largely through analysis of fossils. Phylogeny, the study of the ancestry of species, has revealed that structures with similar internal organization may perform divergent functions. Vertebrate limbs are a common example of such homologous structures. Bat wings, for example, are very similar to hands. A vestigial organ or structure may exist with little or no purpose in one organism, though they have a clear purpose in other species. The human wisdom teeth and appendix are common examples.

Genetic sequence evidence

Comparison of the genetic sequence of organisms reveals that phylogenetically close organisms have a higher degree of sequence similarity than organisms that are phylogenetically distant. For example, neutral human DNA sequences are approximately 1.2% divergent (based on substitutions) from those of their nearest genetic relative, the chimpanzee, 1.6% from gorillas, and 6.6% from baboons. Sequence comparison is considered a measure robust enough to be used to correct erroneous assumptions in the phylogenetic tree in instances where other evidence is scarce. Further evidence for common descent comes from genetic detritus such as pseudogenes, regions of DNA which are orthologous to a gene in a related organism, but are no longer active and appear to be undergoing a steady process of degeneration. Since metabolic processes do not leave fossils, research into the evolution of the basic cellular processes is done largely by comparison of existing organisms. Many lineages diverged when new metabolic processes appeared, and it is theoretically possible to determine when certain metabolic processes appeared by comparing the traits of the descendants of a common ancestor.

History of evolutionary thought

metabolic.]] The idea of biological evolution has existed since ancient times, notably among Hellenists such as Epicurus and Anaximander, but the modern theory was not established until the 18th and 19th centuries, by scientists such as Jean-Baptiste Lamarck and Charles Darwin. While transmutation of species was accepted by a sizeable number of scientists before 1859, it was the publication of Charles Darwin's The Origin of Species by Means of Natural Selection which provided the first cogent mechanism by which evolutionary change could occur: his theory of natural selection. Darwin was motivated to publish his work on evolution after receiving a letter from Alfred Russel Wallace, in which Wallace revealed his own discovery of natural selection. As such, Wallace is sometimes given shared credit for the theory of evolution. Darwin's theory, though it succeeded in profoundly shaking scientific opinion regarding the development of life, could not explain the source of variation in traits within a species, and Darwin's proposal of a hereditary mechanism (pangenesis) was not compelling to most biologists. It was not until the late 19th and early 20th centuries that these mechanisms were established. pangenesis, proposed the theory of punctuated equilibrium in 1972.]] When Gregor Mendel's work regarding the nature of inheritance in the late 19th century was "rediscovered" in 1900, it led to a storm of conflict between Mendelians (Charles Benedict Davenport) and biometricians (Walter Frank Raphael Weldon and Karl Pearson), who insisted that the great majority of traits important to evolution must show continuous variation that was not explainable by Mendelian analysis. Eventually, the two models were reconciled and merged, primarily through the work of the biologist and statistician R.A. Fisher. This combined approach, applying a rigorous statistical model to Mendel's theories of inheritance via genes, became known in the 1930s and 1940s as the modern evolutionary synthesis. In the 1940s, following up on Griffith's experiment, Avery, McCleod and McCarty definitively identified deoxyribonucleic acid (DNA) as the "transforming principle" responsible for transmitting genetic information. In 1953, Francis Crick and James Watson published their famous paper on the structure of DNA, based on the research of Rosalind Franklin and Maurice Wilkins. These developments ignited the era of molecular biology and transformed the understanding of evolution into a molecular process: the mutation of segments of DNA (see molecular evolution). George C. Williams' 1966 Adaptation and natural selection: A Critique of some Current Evolutionary Thought marked a departure from the idea of group selection towards the modern notion of the gene as the unit of selection. In the mid-1970s, Motoo Kimura formulated the neutral theory of molecular evolution, firmly establishing the importance of genetic drift as a major mechanism of evolution. Debates have continued within the field. One of the most prominent public debates was over the theory of punctuated equilibrium, proposed in 1972 by paleontologists Niles Eldredge and Stephen Jay Gould to explain the paucity of transitional forms between phyla in the fossil record.

Social and religious controversies

Stephen Jay Gould from 1871 reflects part of the social controversy over whether humans and apes share a common lineage.]] There has been constant controversy surrounding the ideas presented by The Origin of Species since it was first printed in 1859. Since the early twentieth century, however, the idea that biological evolution of some form occurred and is responsible for speciation has been almost completely uncontested within the scientific community. Most controversy over the theory has come because of its philosophical, cosmological, and religious implications, and supporters as well as detractors have interpreted it as generally indicating that human beings are, like all animals, evolved, and that this account of the origins of humankind is squarely at odds with many religious interpretations. The idea that humans are "merely" animals, and are genetically very closely related to primates, have been independently argued as repellent notions by generations of detractors. Others also intepreted the truth of the theory to imply varying types of social changes — one prominent example is the idea of eugenics, formulated by Darwin's cousin Francis Galton, which argues for the improvement of human heredity by means of political policies. Others have found different political interpretations which have been used as arguments both for and against the theory. The questions raised about the relation of evolution to the origins of humans has made it an especially tenacious issue with religious traditions. It has prominently been seen as opposing a "literal" interpretation of the account of the origins of humankind as described in Genesis, the first book of the Bible. In many countries — notably in the United States — this has led to what has been called the Creation-evolution controversy, which has focused primarily on struggles over teaching curriculum.

Science of evolution

Science: fact and theory

The word "evolution" has been used to refer both to a fact and a theory, and it is important to understand both these different meanings of evolution, and the relationship between fact and theory in science.

Evolution as fact and theory

When "evolution" is used to describe a fact, it refers to the observations that populations of one species of organism do, over time change into new, or several new, species. In this sense, evolution occurs whenever a new strain of bacterium evolves that is resistant to antibodies that had been lethal to prior strains. Another clear case of evolution as fact involves the hawthorn fly, Rhagoletis pomonella. Different populations of hawthorn fly feed on different fruits. A new population spontaneously emerged in North America in the 19th century some time after apples, a non-native species, were introduced. The apple feeding population normally feeds only on apples and not on the historically preferred fruit of hawthorns. Likewise the current hawthorn feeding population does not normally feed on apples. A current area of scientific research is the investigation of whether or not the apple feeding race may further evolve into a new species. Some evidence, such as the fact that six out of thirteen alozyme loci are different, that hawthorn flies mature later in the season, and take longer to mature, than apple flies, and that there is little evidence of interbreeding (researchers have documented a 4-6%hybridization rate) suggests that this is indeed ocurring. (see Berlocher and Bush 1982, Berlocher and Feder 2002, Bush 1969, McPheron et. al. 1988, Prokopy et. al. 1988, Smith 1988) When "evolution" is used to describe a theory, it refers to an explanation for why and how evolution (for example, in the sense of "speciation") occurs. An example of evolution as theory is the modern synthesis of Darwin and Wallace's theory of natural selection and Mendel's principles of genetics. This theory has three major aspects: # Common descent of all organisms from a single ancestor or ancestral gene pool. # Manifestation of novel traits in a lineage. # Mechanisms that cause some traits to persist while others perish. When people provide evidence for evolution, in some cases they are providing evidence that evolution occurs; in other cases they are providing evidence that a given theory is the best explanation yet as to why and how evolution occurs.

The meaning of, and relationship between, fact and theory in science

:Main article: Theory The modern synthesis, like its Mendelian and Darwinian antecedents, is a scientific theory. In plain English, people use the word "theory" to signify "conjecture", "speculation", or "opinion". In this popular sense, "theories" are opposed to "facts" — parts of the world, or claims about the world, that are real or true regardless of what people think. In scientific terminology however, a theory is a model of the world (or some portion of it) from which falsifiable hypotheses can be generated and tested through controlled experiments, or be verified through empirical observation. In this scientific sense, "facts" are parts of theories – they are things, or relationships between things, that theories must take for granted in order to make predictions, or that theories predict. In other words, for scientists "theory" and "fact" do not stand in opposition, but rather exist in a reciprocal relationship – for example, it is a "fact" that every apple ever dropped on earth (under normal, controlled conditions) has been observed to fall towards the center of the planet in a straight line, and the "theory" which explains these observations is the current theory of gravitation. In this same sense evolution is a fact and modern synthesis is currently the most powerful theory explaining evolution, variation and speciation. Within the science of biology, modern synthesis has completely replaced earlier accepted explanations for the origin of species, including Lamarckism and creationism.
Who studies evolution?
Scholars in a number of academic disciplines and subdisciplines document the fact of evolution, and contribute to the theory of evolution.
Physical anthropology
Physical anthropology emerged in the late 1800s as the study of human osteology, and the fossilized skeletal remains of other hominids. At that time anthropologists debated whether their evidence supported Darwin's claims, because skeletal remains revelaed temporal and spacial variation among hominids, but Darwin had not offered an explanation of the mechanisms that produce variation. With the recognition of Mendelian genetics and the rise of the modern synthesis, however, evolution became both the fundamental conceptual framework for, and object of study of, physical anthropologists. In addition to studying skeletal remains, they began to study genetic variation among human populations (i.e.