Greenland Sharks May Be The World's Longest-Living Vertebrates

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Greenland Sharks May Be The World's Longest-Living Vertebrates

Biologists have long suspected that Greenland sharks were ancient animals, but it wasn't until a study published in August 2016 that we knew how old they really were. In the case of one Greenland shark, that turned out to be around 400 years. But without driver's licenses or tree rings to consult, how did the scientists know how old the animals were? The process was understandably tricky.After collecting Greenland sharks that had died from becoming ensnared in fishing nets, the team examined the animals' eye lenses for carbon-14. Carbon-14 is an isotope that filled the atmosphere during the nuclear testing of the 1950s and has diminished at a predictable rate in the years since. This makes it a great marker for the year a cell came into being, since scientists just need to see how much carbon-14 is present, then find the year that quantity matches up with. Using this process, scientists determined that three of their smaller sharks had been born in 1963 or later. By combining that with the knowledge that newborn Greenland sharks are 42 cm (16.5 in) long, they were able to estimate how many centimeters per year the sharks grow, then correlate standard radiocarbon dating with the size of each shark to determine its age. The largest shark was 392, plus or minus 150 years. What's more surprising still is that the size of most pregnant females means that the animals must be at least 150 years old before they reach breeding age. Learn more about these ancient ocean dwellers with the videos below.

Sharks Have Personalities, Too

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Sharks Have Personalities, Too

People have personalities, and most would say our pets do too. But what about wild animals? In two studies, scientists sought to figure out whether sharks all behave the same, or if they exhibit quirks unique to each individual. Researchers from the University of Exeter in the U.K. watched groups of catsharks interact in three different habitats. Even though the sizes of the groups changed, the scientists noticed that the same "well-connected" sharks stayed in their social cliques and less-social sharks hid by themselves regardless of the habitat. In 2015, a study was published in the Journal of Fish Biology that looked at other shark personality traits in two tests. For the first test, the researchers put Port Jackson sharks in a cramped underwater enclosure and timed how long it took each shark to peek out at its surroundings, then finally swim into the open. For the second test researchers stressed each shark by holding it out of the water for 60 seconds, then determined its anxiety level by recording how many times per minute it beat its tail once it got back in the water. In both tests, sharks behaved in many different ways. Some showed boldness by emerging from the box in a matter of seconds while others were hesitant for up to 20 minutes, and their tendencies toward anxiety also ran the gamut. Knowing more about shark behavior may help scientists better understand everything from species evolution to environmental conservation.

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Key Facts to Know

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    Our oceans contain three types of fish: jawless fish, bony fish, and cartilaginous fish. Sharks are cartilaginous fish. 0:38

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    Sawsharks are smaller than sawfish, which can be massive. Sawfish have gills on the undersides of their bodies whereas sawsharks have gills on the sides. 3:40

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    The biggest manta ray every recorded was 30 feet (9 meters) across 4:51

The Shark Cage Was Invented By A Shark Attack Survivor

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The Shark Cage Was Invented By A Shark Attack Survivor

After Fox endured what was, in 1963, the worst non-fatal shark attack in recorded history, he was understandably wary of the water. It was a trip to the zoo that inspired him to build a shark cage—he saw the caged lions and thought to flip the concept, putting humans behind protective bars. (Jacques Cousteau had also built a shark cage before Fox, but his cage was far less secure and had a different design.) Fox became enamored with sharks and their study, and ultimately ended up as a sought-after authority on the predators of the sea.

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from Veritasium

Key Facts to Know

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    Rodney Fox was attacked by a great white shark during a spearfishing competition in 1963. 0:11

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    When he was at the Adelaide Zoo in Australia, Rodney Fox got the idea for a shark-proof cage while looking at the lions. 3:11

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    Sharks don't typically seek out humans to attack—most attacks occur because sharks mistake humans or their equipment for a prey animal. 5:00

Sharks Have Been Around For Longer Than Trees

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Sharks Have Been Around For Longer Than Trees

The earliest sharks swam through Earth's oceans around 420 to 450 million years ago, a time when there were no true trees on land. Paleontologists can trace the history of sharks this far back by examining fossilized shark teeth and scales. About 370 million years ago, sharks appeared in forms that we would find familiar today, though some had spines and bizarre, flat-topped fins.

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Key Facts to Know

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    Sharks have existed for about 200 times longer than modern humans. 0:35

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    Sharks have survived five major mass extinction events on Earth. 0:56

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    The Megalodon shark could have reached 20 meters in length. 1:43

The Shark That Looks Like A Fancy Rug

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The Shark That Looks Like A Fancy Rug

The word "wobbegong" comes from an Australian Aboriginal word that means "shaggy beard." Tasseled wobbegongs are ambush predators—they lie in wait for prey to approach, then dislocate their jaws to bite and swallow the catch. Their teeth point backwards, which ensures a strong grip.

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Key Facts to Know

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    Wobbegong sharks are a type of depressed, or flat, fish. 0:19

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    Wobbegong sharks are often served as part of fish and chips in Australia. 0:59

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    Instead of breathing through their mouths, wobbegong sharks breathe through a set of specialized spiracles on their heads. 1:10