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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.
Parasitic worms in your shellfish lead a creepy...
on June 3, 2020 at 2:22 pm
If you're an oyster lover, seeing a shaggy worm slither across your appetizer is revolting—even though such worms are harmless to people. An internet search using the keywords "oyster" and "worm" will bring up a large cache of images, each one less palatable than the next.
DNA robbery in progress in Australia's copperback...
on June 2, 2020 at 11:41 am
Quailthrush are a group of songbirds unique to our region. They are widespread throughout Australia and New Guinea and there are eight recognized species.
Climate change an imminent threat to glass sponge...
on June 1, 2020 at 3:31 pm
Warming ocean temperatures and acidification drastically reduce the skeletal strength and filter-feeding capacity of glass sponges, according to new UBC research.
Mercury levels in shark fins illegal and...
on May 29, 2020 at 8:17 pm
Shark fins recently sampled from markets in China and Hong Kong contained dangerously high levels of mercury.
Seeing is believing: how media mythbusting can...
on May 26, 2020 at 12:20 pm
As the COVID-19 pandemic has swept the world, politicians, medical experts and epidemiologists have taught us about flattening curves, contact tracing, R0 and growth factors. At the same time, we are facing an "infodemic"—an overload of information, in which fact is hard to separate from fiction.
First fossil nursery of the great white shark...
on May 22, 2020 at 2:37 pm
An international research team led by Jaime A. Villafaña from the Institute of paleontology at the University of Vienna discovered the first fossil nursery area of the great white shark, Carcharodon carcharias in Chile. This discovery provides a better understanding of the evolutionary success of the largest top predator in today's oceans in the past and could contribute to the protection of these endangered animals. The study is published in the journal Scientific Reports.
Researchers reveal origins of complex hemoglobin...
on May 20, 2020 at 3:00 pm
Most biological processes are carried out by complexes of multiple proteins that work together to carry out some function. How these complicated structures could have evolved is one of modern biology's great puzzles, because they generally stick together using elaborate molecular interfaces, and the intermediate forms through which they came into being have been lost without a trace.
Ancient giant armored fish fed in a similar way...
on May 19, 2020 at 11:00 pm
Scientists from the University of Bristol and the University of Zurich have shown that the Titanichthys - a giant armoured fish that lived in the seas and oceans of the late Devonian period 380-million-years ago—fed in a similar manner to modern day basking sharks.
Ecosystem diversity drives the origin of new...
on May 19, 2020 at 5:34 pm
What drives the evolution of new species of sharks and rays? Traditionally, scientists thought it required species to be separated by geographic or spatial barriers, however a new study of elasmobranchs (the group of sharks and rays) has challenged this expectation—and found evolution is happening faster than many think.
Can't touch this! Video shows blacktip sharks use...
on May 13, 2020 at 2:18 pm
It's "hammerhead" time according aerial drone footage of blacktip sharks fleeing to shallow waters when confronted by a huge predator along the coast of southeast Florida. Footage from the drone provides the first evidence of adult blacktip sharks (Carcharhinus limbatus) using shallow waters as a refuge from the great hammerhead shark, (Sphyrna mokarran)—proving you "can't touch this."