7 of the Most Uniquely Fierce Sharks

[ ♪ Intro ] Sharks come in a lot of different shapes and sizes, and not just big, bigger, and “God, help save me!” Worldwide, there are at least 500 different shark species, and most of them aren’t the bazillion-toothed, seal and surfer-terrorizing nemeses of the deep that Hollywood tells us they are. The great white may have a bite force of more than one and a half metric tons and a top speed of 40 kilometers per hour, but that stuff is almost boring compared the other species out there. Because slashing, shredding, and dismembering with mere teeth and/or brute force is not interesting enough for many of nature’s weirdest sharks. No, these sharks went down evolutionary roads that produced adaptations like slingshot faces, chainsaw snouts, glow-in-the-dark skin, and lifespans that rival trees. The Greenland shark looks like a poorly executed granite sculpture of a much more attractive species, and that’s not even the weirdest thing about it. In 2016, researchers discovered that Greenland sharks may be the world’s longest-living vertebrates. The oldest one they tested was at least 272 years old, although it could have been as old as 512. Even the low end of that range is way longer than the previous record-holding vertebrate, the bowhead whale, which lives for about 200 years. Greenland sharks have such a long lifespan that females probably don’t reach sexual maturity until they’re around 150 years old, which seems like a really long time to wait for that first date. Now, we don’t know a ton about these sharks. It hasn’t been that long since we discovered they live so long, and biologists hadn’t studied them much before that. But researchers think the secret to the Greenland shark’s long life might be the bone-crushingly cold water it lives in, which is usually around 1-10 degrees Celsius. The cold water probably lowers the shark’s growth rate, along with its metabolic rate, or how quickly it uses up energy. The cold might even affect its genes. Researchers studying nematode worms have found that cold temperatures can activate anti-aging genes. Sharks are not worms, obviously, but some scientists think something similar might happen for the cold-loving Greenland shark. The genes might help the shark's body fold proteins, for example, keeping it healthy for longer. Misfolded proteins become more common as an organism ages, and they can cause age-related diseases when they accumulate. The cold could also activate genes that help the shark fight off infection or get rid of molecules that could damage its DNA. Either way, some of these sharks, the individual living sharks, have probably been around since before the American revolution. And that is just weird to think about. The thresher shark might seem sort of average at first, that is, until you see its tail. The top half of the shark’s tail fin is as long as the rest of its body, which has inspired all kinds of wild speculation about these sharks taking down their prey Indiana Jones-style. Ridiculous. Until … scientists found out it was true. In 2010, sharks from one species of thresher shark, called the pelagic thresher, were observed literally whipping shoals of sardines with their big long tail fins. The whipping action of the tail fin has been clocked at 129 kilometers per hour, through water! And is so powerful that it doesn’t just kill the shark’s prey, it dismembers it. You can see the advantage: Swiping at a bunch of prey at once means they don’t have to bother chasing around individual fish. And they don’t have to bother with cutting their food up into bite-sized portions, either, since their whip-tail does that for them. I don’t think Indiana Jones ever tried that particular strategy, but maybe he should have. The sawshark, meanwhile, uses a very different weapon for its slicing-and-dicing: its face. It’s like the Leatherface of the deep, with a rostrum, or snout, that looks kind of like a chainsaw, flat and elongated, and lined with modified, teeth-like scales. But the saw is more than just a weapon. Sharks have electroreceptors on their heads called the ampullae of Lorenzini, which they use to sense the electrical fields generated by prey animals. Sawsharks are bottom dwellers, and their ampullae of Lorenzini are located on the underside of the rostrum. That, along with the long, mustache-like nasal barbels located about midway down the rostrum, helps the sawshark locate buried prey. Then, once the shark finds it, it can use the saw to quickly dispatch it. Goblin sharks are kind of the opposite of what you’d expect from a deadly predator: They’re sort of flabby and poorly toned, with long snouts and skin that’s a weird pinkish-gray color. But what the goblin shark lacks in good looks and athletic physique, it makes up for with its own bizarre built-in face weapon: an upper jaw that can be dropped and fired at its prey, and then drawn back again. Kind of like a certain alien that once tried to eat Sigourney Weaver. The goblin shark’s jaw isn’t directly fused to its skull, it’s attached more indirectly, with ligaments and extra bits of cartilage. That’s what makes it so freakishly mobile. The shark stretches the ligaments to draw the jaw back to the rest of its head, then fires it forward by relaxing them. As an added bonus, researchers think the movement might create suction that draws the shark’s prey towards its mouth. So the goblin shark doesn’t just look like a movie alien, it also hunts like one. But there’s a good reason for its strange appearance, too. The shark’s skin is basically see-through because it lives in the deep ocean, where pigmentation is totally unnecessary. And its flabby body is thought to be an adaptation to the energy-deficient environment down there. By not having a lot of muscle, the sharks save the energy they’d otherwise use to maintain it. Goblin sharks are also thought to spend more time hovering than swimming, probably for similar energy-conserving reasons. Although it’s clearly also hovering because that’s just super creepy and it’s really good at that. The wobbegong is more of a stealth killer, with an arsenal of strategies for attracting, apprehending, and ambushing prey. The shark has wiggly lobes on its upper lip, which to prey, look like yummy things to eat, or maybe a safe place to hide. Except that really, the prey are the yummy things to eat, and the lobes are the opposite of a safe place to hide. Scientists think the lobes also help the wobbegong blend into the ocean floor, where it spends most of its time. Because its prey often comes to it, the wobbegong doesn’t have to waste a lot of time and energy hunting its food. It just hangs out and waits for its takeout order to arrive, usually in the form of fish, cephalopods, and other small, doomed creatures. Prey doesn’t even have to come very close, because the wobbegongs can send their mouths out to meet their prey, independent of the rest of their bodies. One species, the spotted wobbegong, can extend its mouth further than the length of its own head. Like the goblin shark, the motion enlarges the shark’s mouth, which also generates suction that traps prey as it passes by. And if that doesn’t work, they do have another option: some wobbegongs have been observed sneaking up on their prey. Extra, super creepy. The frilled shark, named for the frills on its gills, is sort of like an eel, sort of like a snake, and sort of like a thing that tried to eat the Millenium Falcon in the Empire Strikes Back. What it’s not very much like is a shark, at least not most sharks as we know and recognize them. It really looks much more like an eel … until you see its bizarre, backward-facing teeth. Scientists think these strange teeth might be used to lure prey. They’re bright white and stand out against the dark skin of the shark, so curious fish might be tempted to come in for a better look. Since the teeth face backward, they hook the prey and make it very hard to escape. The frilled shark’s mouth is also long and flexible, like a snake’s. That allows it to open its mouth really wide, swallowing prey up to half its body length. Frilled sharks live at depths of 120 to 1,200 meters, and they aren’t seen very often, so we don’t know exactly what their feeding behavior looks like. But scientists think the arrangement of the shark’s fins, combined with its natural buoyancy, suggests that it might, like, hover in the water, and then strike at passing prey like a snake. The catshark doesn’t have a whip for a tail, or a saw for a head, or hooks for teeth. It has a different type of clever adaptation that helps it survive 500-600 meters below the surface, where it lives: it glows in the dark. Catsharks are biofluorescent: They have special pigment in their skin that absorbs blue light, the only color that penetrates that far into the ocean, and then re-emits some of the energy as green light. This strategy isn’t as common as bioluminescence, where an organism produces its own light through a chemical reaction. But scientists are starting to realize that biofluorescence is more widespread among fish than we thought. It’s just been hard to detect it because the glow is often too dim for us humans to see without special equipment. And in 2016, researchers discovered it in catsharks. The sharks’ eyes, which are shaped like a cat’s, are much more sensitive to light. They’re attuned to the blue and green part of the spectrum, and they have long rod cells that help them see better in low light. So they can probably see the biofluorescence pretty clearly. We aren’t totally sure what they use it for, but the researchers think the green glow helps the sharks see each other in the dark. More specifically, it could help them find mates, an idea that’s backed up by the fact that males and females have different glowing patterns. In at least one species, the males’ claspers, which they use to mate, are part of that pattern. There’s still a lot we don’t know about why some sharks glow, or about most of the unusual qualities on this list. But one thing is for sure: To find the truly awesome sharks out there, you have to look past those plain old boring Hollywood sharks to their lesser-known but weirdly fascinating cousins. Happy swimming, everyone! Thanks for watching this episode of SciShow! If you’re interested in learning more about some of the strangest animals out there, along with all kinds of other fascinating science, you can go on over to youtube.com/scishow to subscribe. [ ♪ Outro ]

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