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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.
Sharp increase in Ningaloo whale shark injuries...
on January 24, 2020 at 9:39 am
Almost one-fifth of the whale sharks (Rhincodon typus) in Western Australia's Ningaloo Reef Marine Park show major scarring or fin amputations, with the number of injured animals increasing in recent years, new research reveals.
Large marine parks can save sharks from...
on January 23, 2020 at 4:00 pm
'No-take' marine reserves—where fishing is banned—can reverse the decline in the world's coral reef shark populations caused by overfishing, according to an Australian study.
Shark attacks remained low in 2019—but bites...
on January 23, 2020 at 3:00 pm
Shark attacks were unusually low for the second year running, with 64 unprovoked bites in 2019, according to the University of Florida's International Shark Attack File. The total was roughly in line with 2018's 62 bites and about 22% lower than the most recent five-year average of 82 incidents a year.
Deep-sea osmolyte makes biomolecular machines...
on January 22, 2020 at 2:02 pm
Researchers have discovered a method to control biomolecular machines over a wide temperature range using deep-sea osmolyte trimethylamine N-oxide (TMAO). This finding could open a new dimension in the application of artificial machines fabricated from biomolecular motors and other proteins.
Walking sharks discovered in the tropics
on January 21, 2020 at 1:10 pm
Four new species of tropical sharks that use their fins to walk are causing a stir in waters off northern Australia and New Guinea.
Fins and limbs tell evolutionary tale
on January 17, 2020 at 2:41 pm
About 400 million years ago, our early ancestors took their first hesitant steps out of the primordial seas on to land.
Sea lions: Cash cows in the Bay Area, but farther...
on January 17, 2020 at 2:06 pm
Sea lions are increasingly living in parallel universes along the California coast, a disparity best observed amid the noisy, stinking spectacle that rolls out daily at San Francisco's Pier 39 shopping center.
Mobile protected areas needed to protect...
on January 16, 2020 at 7:00 pm
World leaders are currently updating the laws for international waters that apply to most of the world's ocean environment. This provides a unique opportunity, marine scientists argue this week, to introduce new techniques that allow protected zones to shift as species move under climate change.
Discovery reveals how remora fishes know when to...
on January 16, 2020 at 7:55 am
Remoras are among the most successful marine hitchhikers, thanks to powerful suction discs that allow them to stay tightly fastened to the bodies of sharks, whales and other hosts despite incredible drag forces while traveling through the ocean. But how do these suckerfish sense the exact moment when they must "stick their landing" and board their speedy hosts in the first place?
Old fishing hooks are severe hazards for sharks
on January 15, 2020 at 1:53 pm
Startling data fresh off an eight-year tiger shark study in French Polynesia shows severe impacts the creatures of the sea face long after they are cut loose from fishing lines.