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Tree of Life
Plant Flower, Tree
Invertebrate Octopus, Ant, Bee, Butterfly, Spider, Lobster
Vertebrate Fish, Seahorse, Ray, Shark, Frog, Turtle, Tortoise, Dinosaur
Bird, Ostrich, Owl, Crow, Parrot
Mammal Bat, Rabbit, Giraffe, Camel, Horse, Elephant, Mammoth
Whale, Dolphin, Walrus, Seal, Polar Bear, Bear, Cat, Tiger, Lion, Dog, Wolf
Monkey, Chimpanzee, Human
These are organized by a classification scheme developed exclusively for Cosma. More…
shark : any of numerous mostly marine cartilaginous fishes of medium to large size that have a fusiform body, lateral branchial clefts, and a tough usually dull gray skin roughened by minute tubercles and are typically active predators sometimes dangerous to humans — Webster
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term “shark” has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus, as well as other Chondrichthyes such as the holocephalid eugenedontidans. Under this broader definition, the earliest known sharks date back to more than 420 million years ago. Acanthodians are often referred to as “spiny sharks”; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole.
Since then, sharks have diversified into over 500 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length. Sharks are found in all seas and are common to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can survive and be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.
Well-known species such as the great white shark, tiger shark, blue shark, mako shark, thresher shark, and the hammerhead shark are apex predators—organisms at the top of their underwater food chain. Many shark populations are threatened by human activities. — Wikipedia
10 Best Places to Swim With Sharks (Professional Association of Diving Instructors, Condé Nast Traveler)
25 Best Destinations for Sharks and Adventure (Travis Marshall, Scuba Diving)
Shark Diving Tips and Advice (Shart Trust)
10 Shark Diving Tips (Dive Magazine)
Phys.org - latest science and technology news stories Phys.org internet news portal provides the latest news on science including: Physics, Nanotechnology, Life Sciences, Space Science, Earth Science, Environment, Health and Medicine.
There's a giant 'Green Banana' off Florida's...
on September 30, 2020 at 7:10 pm
If you haven't heard of the "Green Banana blue hole" you might imagine a tropical cocktail you can order in Key West, or a dessert you ordered after a night on Bourbon Street.
New study reveals how reptiles divided up the...
on September 30, 2020 at 12:07 pm
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In a field where smaller is better, researchers...
on September 29, 2020 at 4:05 pm
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Study traces the evolution of gill covers
on September 29, 2020 at 7:20 am
The emergence of jaws in primitive fish allowed vertebrates to become top predators. What is less appreciated is another evolutionary innovation that may have been just as important for the success of early vertebrates: the formation of covers to protect and pump water over the gills. In a new study published in the Proceedings of the National Academy of Sciences (PNAS), USC Stem Cell scientists and their collaborators have identified a key modification to the genome that led to the evolution […]
The pace of environmental change can doom or save...
on September 28, 2020 at 7:00 pm
Increasing fishing too quickly can cause coral reef ecosystems to collapse, new University of Colorado Boulder-led research finds.
Invasive sea lampreys in Great Lakes, and the...
on September 28, 2020 at 5:20 pm
It's a mystery. Invasive sea lamprey, the Great Lakes' biggest predator, primarily feed on lake trout, one of the lakes' most prized sports fish. When trout populations are high, researchers expect to see fewer lamprey-wounded fish, and more of those wounds when lamprey populations are spiking.
New marine protected areas connect hundreds of...
on September 25, 2020 at 5:22 pm
Three hundred and fifty square kilometers of Turkey's coastline has been brought under environmental protection in a recent announcement by the Turkish government. This new area represents a significant expansion of the existing marine protected area network along the country's Mediterranean coast and firmly establishes Turkey as a leader in marine conservation in the most overfished sea on the planet.
Whale rescuers face grim task in Australia mass...
on September 25, 2020 at 7:59 am
After days wading through chilly waters, surrounded by the pained cries of hundreds of stranded whales on Australia's south coast, rescuers faced the grim task Friday of disposing of the carcasses.
Australian rescuers forced to euthanise some...
on September 24, 2020 at 8:19 am
Australian rescuers were forced Thursday to begin euthanising some surviving whales from a mass stranding that has already killed 380 members of the giant pod.
Open-ocean fish farm proposed off San Diego coast...
on September 21, 2020 at 8:20 pm
A prestigious San Diego research institute and a Long Beach social benefit investment group are teaming to create what could be the first fish farm in federal waters.