True Facts: The Curious Adaptations of Sharks

This right here is a little baby shark. It's cute, isn't it? Rubbing up on that veiny sack. This one was laid as an egg and then abandoned, left to fend for itself. Well, not entirely. The mother did leave it attached to that ball. It is a yolk sac and contains enough food to get the baby through to hatching. Provides a bit of comfort, too, by the looks of it. It's like a stuffy and mushy peas all wrapped up in a testicle. Now, shark eggs come in all sorts of different shapes and sizes, with different ways of attaching to crap on the seafloor. This sex toy here is actually the egg of a crested horn shark, and it's thought to blend in with the kelp that it's often found in. But listen, being an abandoned egg can suck. Literally. This is a Port Jackson shark sucking out the insides of one of those eggs. It's using that bottom-of-the-ice-cream-cone technique, too. Knows what it's doing. In many species of shark, though, the eggs hatch inside the mother, where the embryos then develop. The embryos start off with yolk sacs just like the ones you see in eggs, but often the pregnancy lasts longer than that food supply does. But baby's gotta eat, and the mother has to figure out how to give it more food. Sometimes it's a nutritious mucus. In the case of the great white shark, the mother creates unfertilized eggs, which the embryos can gobble up with their tiny little teeth. And it's not all just sitting around and waiting in there. Some babies can be quite active. Here you can see a tawny nurse shark embryo swimming freely between its mother's two uteruses. It's cute, right? Inside, there are often embryos from different fathers. And one thing this baby is doing is looking around for half-brothers and half-sisters to snack on. Not even born yet, they're in a Game of Thrones situation. Now apparently these babies peek out of their mother's cloaca as they're swimming back and forth between her two uteruses. You just saw it, didn't you? I know you did. Right there. That's the Gerber baby. That's where they come from. Once born, sharks are endowed with a number of amazing adaptations. Many sharks can swim very quickly. Jerry, what's this footage? Well, I'm saying swim quickly, and this one's walking. What is it? Epelich shark? Well, whatever it's called, it's going to ruin the reputation of the rest of the sharks. Try putting that in a scary movie, Jerry. Look out, shark! Everyone walk at a moderate pace in the opposite direction. It'd be a disaster. All right, let's try this again. Many sharks can swim quite quickly. This comes in handy because sharks live in places where there are sharks. And also because the pancakes they eat don't exactly lie still on a plate. Run away, pancake! Now, it's not all that easy to move quickly through water. If you've ever done water aerobics, then you've probably felt like an idiot. But you've also probably felt that water pushes back on you when you move. Like most fish, sharks move their powerful tails back and forth to move forward. But as they move forward, they also have to stay up. Most fishes use swim bladders to stay buoyant. Imagine you swallowed a condom you'd blown up with air, Jerry. Why is it a condom, Jerry? It's just a balloon. No, it doesn't make it more relatable. Sounds filthy. Anyway. Sharks don't have swim bladders, but they have some tricks to lighten up. They have a very fatty liver, which helps. And a skeleton made out of cartilage instead of bone. Every time you look at a shark, your ear whispers to your nose, that could have been us. But even with all that, sharks have a tendency towards the sinking. So, to stay afloat, many sharks take advantage of lift. Certain shapes at certain angles cause fluids to move more quickly over one surface than the other. You may have heard that the water on top moves faster because it has to reach the end at the same time as the water on the bottom. Science hippies at Cambridge showed that that's just not true. The water on top moves quite a bit farther in the same amount of time. Anyway. The end result is that there's a difference in pressure between the top and the bottom, resulting in a force that pushes in the direction of the lower pressure. The fins of many sharks are just the right shape to take advantage of lift. The hammerhead takes advantage of all of it. Here you can see how to put one back together, if you break it. They will often swim at an angle, getting lift from their side fins as well as the one on the top. Now, you've probably noticed that water can get a bit mushy-mushy when it passes quickly over a fin. This is called mushy-mushy or turbulence. If you've ever been in a waterpark wave pool, then you've felt what it's like to be covered in urine. But you've also felt how swirling water can complicate movement. If the water gets too swirly-swirling, it can be hard to push against it. And it can counteract lift. So sharks have evolved some special tricks to reduce turbulence. This one's a shady one, isn't it? Look at that side eye. Brilliant.org is a great way to learn. You know how some sharks have to keep swimming to stay alive? Well, it's like that with learning. Well, I don't mean you're gonna die if you don't. But a lifetime of learning keeps you sharp and in step with how the world is changing. Brilliant teaches you about math, science, and computer science in an engaging, hands-on way. These interactive, bite-sized lessons keep you engaged and let you learn at your own pace, even if you only have 15 minutes a day. And that's important, especially if you want to tackle an area that might have intimidated you in the past. We all have them. Come on, statistics? There are thousands of lessons with new ones added each month. They teach you fundamental concepts about how the world works and they can open up new opportunities for how you approach your work. To try everything Brilliant has to offer, free for a full 30 days, visit brilliant.org slash ZeFrank or click on the link in the description. The first 200 of you will get 20% off Brilliant's annual premium subscription. Brilliant has been a long-time sponsor of this show and I'm a fan. Please check them out today. Where were we? Oh, right. Sharks have evolved some special adaptations to reduce turbulence. Their skin is covered with denticles. Not like denticles of the octopus, but rather denticles which are made from exactly the same thing that teeth are made out of, dentin and enamel. Science hippies dented these testicles, sorry, tested these denticles to see what effect they have on the flow of water around the shark. The tips of the denticles interact with the fast-moving water, but between them, water is sort of trapped in an eddy. An eddy doesn't like that one bit. The net result is that less of the surface of the shark is interacting with the faster flow. This means less drag and more efficient swimming. Listen, you try to swim in drag, your boa gets all tangled and never mind the petticoat. Now the shortfin mako is the fastest shark, reaching speeds of 70 to 100 kilometers an hour. They have special denticles. If water begins to curl backwards on their skin, creating drag, their denticles pop up and trap that backward-flowing water, which reduces the drag and lets them swim faster. But having your body covered in teeth has some other benefits. I mean, it's like having a little coat of armor. The whale shark, for example, has an interesting challenge. Its eyes protrude from the sides of its head. You know, you're going to bump those into the corner of a coffee table. So you know what they did? They put some armor right on their eyeballs. So they can take a scratch or two. And if that's not enough, they can also retract their eyeball into their head. I mean, you could lose a ping pong ball in that hole. Want to see it from the inside? Ready? Yoink. Now other fish figured out that if you rub against the grain, those denticles can be used as an exfoliator. Scratchy scratchy. I mean, it comes with some risks, I suppose. It's like using a lion's mane for a hand towel. Personally, I prefer my conveniences be a bit farther from a set of teeth. Now in some sharks, denticles seem to play a very different sort of role. These sharks have photophores, cells that can create light. In fact, a shark, the kitefin shark, is the largest bioluminescent vertebrate. Oftentimes, they have a lot of these photophores down on their underpants. So that when you look up at them, they blend in with the light coming down from above. You can hide from other sharks or something that you plan on eating. The denticles that surround these photophores seem to act like little light diffusers, creating a more even glow. Other sharks can glow, but in a different way. Two species of cat shark have cells that fluoresce, meaning that they don't generate light. But rather, they take in one wavelength of light and use it to emit a different wavelength of light. In this case, they take in blue and spit out green. You can see that some of these denticles are transparent, allowing the light to shine through. Even their eggs glow. Now this sort of glowing seems to be more about visual communication between the sharks. Males and females have different patterns, and it's possible that other fish can't see this light that they emit. So the cat shark can be camouflaged for an ambush, but perfectly visible to a potential mate, like cracking a glow stick at a rave to get someone's attention. Now up close, sharks do rely on their vision to communicate and to hunt. But sometimes the water can get murky, and some things that are delicious bury themselves under the sand. To help with this, sharks have another set of sensory organs. Right there, all those little holes that look like a five o'clock shadow, those are ampullae of Lorenzini, the second most fun-to-say organ, right behind islets of Langerhans. The little pores lead to canals which are filled with a conductive jelly. Looks a bit like Vaseline when you squeeze it out. I mean, I'd be doing that all day. Nerve fibers are in contact with the jelly and can sense small changes in electrical potential or voltage. Now living things have electrical fields around them which can change when charged ions move suddenly between membranes, like when you flex a muscle, for example. Even shark babies can sense changes in this electrical field. Watch this one, an electrical field is about to be turned on. There, look at that, it becomes completely motionless. Hammerheads have a whole bunch of these sensors, up front on their face where evolution stepped on them. Now the sawfish is not a shark, it's a ray, which is closely related. It has sensors all up and down that front bit. It's rostrum. Certainly comes in handy when your eyes are on the top and your mouth's on the bottom. It uses that rostrum sort of like an old man with a metal detector. You know, out there alone, sweeping it back and forth. Sometimes doesn't even turn it on, just doesn't want to say hi to people. Anyway, if the rostrum does detect something, conveniently it doubles as a weapon. And listen, it uses it exactly like you would if you had one of those things. And if they're not slicing at it, they can use their rostrum to press their prey against the ocean floor until they can slurp it up. Now, unlike sawfish, sharks often don't have something to push up against when they catch their food. I mean, eating underwater can be challenging with your food floating around like that. Look at those two little fish out on a risky first date. If you've ever bobbed for apples, then you know what it's like to have a mouthful of other people's saliva. You also know that in water, it can be difficult to get things in your mouth without the use of hands. But sharks have figured out a few ways to go about it. One approach is called ram feeding. Sort of a floating orifice or flashlight of the sea. Perhaps fellatio as yet unrealized. It's essentially just opening your mouth and swimming. But that's different than what this whale shark is doing, which is called suction feeding. Stop it. It repeatedly opens its mouth and creates negative pressure, sucking in water and the tiny things that it eats. Also bubbles. They like the bubbles. I imagine it's sort of like underwater pop rocks or some sort of extreme whale shark diet. No, seriously, it fills you up. Now, don't start thinking that it's all soft up front like grandma's gums. Even whale sharks have 6,000 tiny, tiny teeth. They just start using them. Many other sharks, of course, do use their chompers. It's a good set of utensils to have if your leftovers are larger than you are. And listen, if you spend a lot of time chasing something, it's good to be able to hold on when you catch up. One of the most impressive, though, is the cookie gutter shark. There it is with the old number two. I mean the pencil, not like... All right. Doesn't look that bad, does it? Here's what it looks like from the bottom. Mutant zombie penis vibes. Their bottom teeth are fused and their mouths appear to be able to create suction. Their bites look like someone used an ice cream scoop. A lot of people say these sharks spin to create that shape, but there's no evidence for that, and it's probably bulls**t. Anyway, other sharks, like those in the genus Squatina, got tired of the chase. They bury themselves. Naked, face down, sandin' your naughty bits, just sayin'. But if a fish comes along, it's f**ked. I know what you're saying. What happens when sharks get horny? It's the best segue. Well, I'll tell you forthwith. These are basking sharks, and it's thought that this circling is part of their mating behavior. You know, check out the tail you might want to get with. As with most fish, they can't talk, which actually probably makes it easier to flirt. They use signals, like the classic head bob. Yeah, I see you. And if they're into it, they might turn over and show you the rest of the package. It's quite cute, almost refined. With other sharks, it's more like trying to meet someone in a mosh pit at Coachella. It's a f**kin' mess. That guy knows. Foreplay can be a bit rough. Many sharks have a kink around biting. Get yourself a mouthful of fin. I mean, this right here looks downright romantic. And you can't blame them for trying to get a bit of grippage. You try having sex in the deep end with nothing to hold on to. You tell me what went where in the end. The male must insert his double penis- Jerry, it's not a double penis. They're called claspers. I know, but just because it looks like one doesn't mean it is. I mean, if that were true, we'd be in a pickle. I mean, right there, pickles. You want a jar of d**ks, Jerry? Anyway, claspers are modified fins. He's got two because it all goes down from the side. And with all this rolling around, you don't know what side you're gonna be on. When inserted into the female's cloaca, the ends of the claspers in some species open up like a little umbrella. And a little siphon pumps water and sperm up in there. And soon enough, there'll be more little shark babies. Look at that turtle back there. I mean, that's a dirty turtle. What else? What do you mean, Jerry? Oh, you mean if things that look like penises were actually penises? Well, your fingers, for one. And the number one for that matter. You'd have to count down from three to penis using your penis fingers, Jerry. And never mind drinking your soda pop through a straw. I mean, that'd be some surprise, wouldn't it? Just be glad things are the way they are. On the tree.