Why Don’t Sharks Have Bones?

Why Don’t Sharks Have Bones?


Hello! This week is Shark Week on the Discovery
Channel, which some of us here on the internet aren’t huge fans of, so instead of sensationalizing
sharks or just making stuff up about megalodons still existing, we thought we’d talk about
science with the understanding that reality is actually pretty fascinating. Sharks and rays and skates are probably the
most complex organisms that don’t have bones, but does this mean that they’re less developed?
No! Sharks are simply part of a different class of fish. Literally, the class chondrichthyes,
which includes sharks and skates and rays and a very small group of various small little
things called holocephalis. Those are all fish with jaws and scales and chambered hearts
and a skeleton made out of cartilage. [Intro] Bones are awesome. They provide a nice rigid
internal structure, they produce red blood cells and provide firm anchors for our muscles
to attach to so we don’t just slump to the ground in a pile of goo. Indeed bony fishes,
osteichthyes, are the largest class of vertebrates in the world, with over 28,000 species. Now sharks might look like just another fish
to you, but bony fish are actually more closely related to us than they are to sharks. Terrestrial
vertebrates like us only diverge from fish around 300 million years ago while chondrichthyans
and osteichthyans broke off from each other around 400 million years ago. For all that
time, sharks and other chondrichthyans have been evolving parallel to bony fish, and boy
do they have some weird features to show for it. Sharks actually split off from fish before
the development of scales, and yet both sharks and bony fish have scales, or do they? Turns
out, shark scales evolved completely separately and are thus completely different. Sharks
didn’t have the necessary biochemical machinery to make scales. However, they did, pretty
obviously, have all of the systems in place for creating teeth, so their scales, which
cover their body, and each are fed by blood vessels, are covered in, get this, dentin,
the same stuff that makes up the inner layer of your teeth. So sharks don’t really have
scales so much as skin teeth, and indeed shark scales are sometimes referred to as dermal
denticles. Sharks also have red blood cells, but we know
that red blood cells are made inside of bones, right? Well, not 400 million years ago they
weren’t. Sharks produce red blood cells in their spleen as well as their epigonal organ
which surrounds their gonads and in a bunch of tissue around their esophagus called the
Leydig’s organ which is unique to chondrichthyans. So we’ve gone some way in discussing HOW sharks
can survive without bone, but that doesn’t help us understand why. I mean there are lots
of classes of fish that weren’t able to overcome extinction events or that were outclassed
by bony fish, so how come sharks, at the tip top of the food chain, manage to survive despite
their seemingly primitive skeletons? Well, that’s kind of going about it the wrong way.
The question isn’t so much why the top predators of the sea have cartilaginous bones, it’s
how a cartilaginous skeleton helps an animal be an effective predator. Because obviously
it does. If it didn’t, they’d be extinct. Okay, so ecologically we know that predators
have to have wider ranges than prey animals. They also have to be as fast or faster than
their prey, and possibly even more important than that, they have to be maneuverable. So
how does cartilage help? Well, first and most simply, cartilage is lighter and more flexible
than bone allowing sharks to weigh less and bend their bodies at sharper angles than bony
fish. It’s a nice combination that increases both power and maneuverability. But that’s only half the story, and here’s
where we get to the true weirdness of the chondrichthyans. Because unlike pretty much
every other vertebrate, most of their muscles don’t even connect to their skeleton! Now of course some muscles do connect to a
shark’s skeletal tissue, their jaws being the obvious example, but their primary locomotive
muscles connect to a stretchy, helical network made of collagen that’s just beneath their
skin. Arthropods use a similar arrangement. Their muscles connect directly to their exoskeleton
which, if you’ve ever been chomped on by a crab, you know is a pretty efficient arrangement.
By grabbing and pulling on the outside of the animal rather than connecting to the spine,
the muscles have greater leverage. Cooler still, this collagen framework acts
kind of like a rubber band or a spring. As the shark bends itself, the collagen stretches
on one side and energy is stored in that tissue. Then the shark simply has to relax for the
collagen to push itself back into place and even over correct a little into the next push
of its tail. The energy of every push helps fuel the next one. So, there you have it! Sharks — their lineage
may be older than those young bony fish, but that doesn’t stop them from sitting happily
atop the oceanic food chain. Thanks for watching this episode of SciShow
and choosing science over sensation. Some other YouTube channels are talking about the
science of sharks this week as well, including It’sOkToBeSmart and on the Brain Scoop there
will be five full days of shark stuff. Check it out and enjoy and thanks for watching SciShow.

Randy Schultz

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100 thoughts on “Why Don’t Sharks Have Bones?

  1. swapertxking says:

    ah, the modern miracle of science.  turns out we are not related to bony fish in the way we thought.  we are more closely related to placoderms,.

  2. Kunj Bhuva says:

    Do ants have bones ….?

  3. Nolan Westrich says:

    You don't have to be faster or even as fast as your pray. Humans are very slow, compared to the animals they hunt.

  4. Sami Stark says:

    love how excited and almost out of breath he is about this (may have been late uploading but hey it was good still tho
    )

  5. Dami Williams says:

    I liked this video but would have benefitted from a visual of the cartilage skeleton and the muscle – collagen network

  6. reaperofthedamned07 says:

    Can I get i get uh…?️oneless shark?

  7. BerK says:

    GET THIS! 2:01

  8. Dequavis Hardaway says:

    i thought orcas was the top predator of the sea?? or maybe its the ocean…

  9. Ava Gibbs says:

    You should run your own shark week on your channel

  10. Karim Wassef says:

    why don't most fish have cartilage instead of bone… If cartilage is superior, why bone?

  11. Seth Begley says:

    2:36 Jesus Christ. That shark is so fat.

  12. Sergio Carranza says:

    Boneless

  13. Sergio Carranza says:

    Boneless

  14. Pixx says:

    You: Scales
    Me, an intellectual: Skin teeth

  15. GotPotatoes24 says:

    Unrelated, but I'm pretty sure at 2:40 that's a pregnant gal swimming around!

  16. Candy Domination says:

    Why when you brings dogs inside from playing outside they have that "dog" smell, but the same can not be said for humans?

  17. Gosia Hasal says:

    B O N E L E S S

  18. David says:

    Hank looks like he just got in from a massive weekend long bachelor party.

  19. Wither says:

    great whites always look like they are smiling for the camera

  20. candlewax122 says:

    I choose to believe megalodons still.exist

  21. Eric says:

    Boneless pizza and boneless sharks

  22. Charles Arthur Brennan says:

    liking purely for the shade at the start of the video

  23. ViraIshnia says:

    Lol, love the Megaladon shot

  24. J Smith says:

    All sharks are ?️oneless fish

  25. ccggenius12 says:

    So, the traditional method of preparing wasabi technically requires that you let a shark pre-chew your condiment? Neat.

  26. Jake Engdahl says:

    when she tickles the Denticles on your gonads

  27. MoonLight - says:

    Sharks have bones

  28. Dank McMemes says:

    Cus dey B o n e l e s s

  29. fans group Fan's group says:

    a tatle

  30. fans group Fan's group says:

    are you mad

  31. fans group Fan's group says:

    you are donkey

  32. fans group Fan's group says:

    humans Skelton

  33. Karen Piscopo says:

    Sharks have bones look up shark skeleton! The only bones they have are in the fins, jaw, teeth, vertebrae and ribs!

  34. San dro says:

    So sharks most advanced animals without bones? What about Octopus?

  35. Rhys Logan says:

    Science is my sensation

  36. xrated shkinny says:

    sharks do have bones jus watched a man cook one an separate the bones

  37. Miss Misstery says:

    Are there types of sharks with bones? Cause in museums and stuff there are shark bones hanged on ceilings

  38. CerberaOdollam says:

    So if you escape by the skin of your teeth….you're a shark?

  39. Goldsword Animations says:

    Watch out for sharkastic comments.

  40. Ellie Nixon says:

    Can I get my shark ?️oneless?

  41. ايوه نعم says:

    This guy's body language really sucks

  42. ProjectiluvOP says:

    Boneless fish

  43. Christian Noll says:

    Shark week/discovery channel used to be good. Not so much anymore smh

  44. XXX_insane_gamer_XXX says:

    soooooooooooooooooooooooooooo boring

  45. Bowley4 says:

    This is by far the most “WAIT WHAAAAT?!” Video I’ve ever seen on this channel. I feel like i was lied to my whole life(nobody ever mentioned this before now) and learned so much so fast I’m just astonished. Amazing

  46. M H S says:

    I have a boner

  47. Ace says:

    Hi sci show please do a video on why we don't see transitional skeletons of animals during their evolution.

  48. Poopsie Pop says:

    uhhhh can I have some ?oneless shark?

  49. Agus Rossi says:

    Really interesting But, why does the fiver rises up at night?

  50. William Shreckengost says:

    Woah. Sharks are pretty awesome, and YouTube is pretty late in suggesting this one to me.

  51. ResidentEvil302cuba rican215 says:

    I never knew this.. learn something new everyday

  52. Mojos Bigstick says:

    I just love the word elasmobranch.

  53. Recruit Lucier says:

    Why I don't go into the ocean: this entire subgroup of specific species.

  54. Arthur Williams says:

    I got Stockholm Syndrome for sharks when I did a shark cage dive in Hawaii a few years ago. They didn't want to hurt us at all, but so many had fishing hooks trailing from their mouths and fins. One had clearly been hit by a boat propeller, because it had three jagged scars along it's back. We were more dangerous to them them then they were to us.

  55. KGF_V1P3R says:

    I found this video when I searched up can sharks have ebola

  56. The Lone Dovahkiin says:

    Just opening the video with some massive shade

  57. Gabriel Grigore says:

    Wait they dont???

  58. Downfall says:

    Hey, I wonder how it feels to have barely any bone in your body.

  59. Bloody Idiots says:

    ?oneless.

  60. Manuel Alejandro Ordonez says:

    can we preserve shark bone

  61. Manuel Alejandro Ordonez says:

    orca(killer whale) eat sharks

  62. sdfkjgh says:

    Skin Teeth actually sounds like an SCP.

  63. Christopher Sweezey says:

    I think you burned Shark Week too hard…

  64. John Michael says:

    Sharks are cool!

  65. One Punch Man says:

    If sharks have no bones….
    Why its a vertebrate???

  66. Sir Loin Of Beef says:

    It's
    BONELESS

  67. IntermediateJesus says:

    Sharks are literally made out of teeth.

  68. Bram Jans says:

    I once dissected a shark, them having no big tough bones made it quite easy, although I didn't expect them to have such a big liver.

  69. Bram Jans says:

    Sharks on top of the oceanic food chain? Orca sais no

  70. Skater Boy says:

    "Why don't Sharks have Bones?"

    They have teeth made of bone

  71. Car C says:

    Dudes amped up in this one…

  72. VampireDucks says:

    Discovery Channel deserved that. Kpow!

  73. Wayne Hasch says:

    Is this guy on meth OR angel dust ??

  74. Dad Bod says:

    What would happen if our muscles connected to our skin? Would we have better leverages and be stronger? Or would our skin rip from the immense pressure?

  75. Chelsey Abbott says:

    THANK YOU! its so rare lately to find a real shark week documentary and not just a "killer shark eith a taste of prey" show

  76. Tragoudistros.MPH says:

    I had no idea their muscles connected to their skin! That's amazing!

  77. Born BredBermudian says:

    One thing I'm still confused about. If we diverged from fish like sharks did, but later. And we're obviously not considered fish, why are sharks considered fish still? May be a dumb question but I'm just wondering.

  78. Duffy Mullaney says:

    Im terrified of the sight of sharks… But they fascinate me… And I love scishow… This is gonna be a long episode

  79. Hawkeye Stegosaurus says:

    I never thought about why sharks don't have bones, but now I know and it was a thrill ride of emotions.

  80. patrick murphy says:

    This was very interesting! Thanks!

  81. Michael Elbert says:

    Sharks do have bones they have it two Jaw bones

  82. Rhys says:

    Dude whats the rush, slow down with the talking man I had no idea what youre saying

  83. Reece Harbottle says:

    Sharks do have bones but made up of cardilage where after the thing dies the bones dissapear

  84. j k says:

    But … I wanted to hear about the chambered heart made of cartilage!

  85. Terilee Bruyere says:

    What a lovely smile on the White Shark's face. {Camera man} "Say cheese"

  86. wintertide wolf says:

    Hank threw shade this whole episode.

  87. Amanda LeBlanc says:

    I just want to express how much I appreciate your intro (and the content, of course).

  88. Gerald Barnes says:

    There fish

  89. Gerald Barnes says:

    Fish,reptilian,and mammal

  90. Krueger's Kid says:

    Why do people continue to say sharks are at the top of the food chain when we know it's Orca as the one true apex predator.

  91. Greg Hamilton says:

    Seriously, Hank, you've gotta stop doing so much coke before you appear on camera.
    Your voice & mannerisms are getting into the realms of parody lately. (You're more like a marionette than a man!) It can't be good for your health either…
    Why don't you take a break, get yourself cleaned up & let Olivia take over for a while?

  92. Digital Bear says:

    If every teacher was like you, I guarantee kids would love school and pay more attention in class.

  93. Quinn Ethan says:

    SHARKS DONT HAVE BONES?

  94. karora yendrembam says:

    What about teeth… ????

  95. GODDAMN BUBBLES says:

    lol this guy sounds like he's hopped up on coffee!! XD

  96. Abhishek Raj says:

    Sharks hv 7 bones

  97. John Bear says:

    Red blood cells are also created in the lungs, and liver.

  98. Takashi Kurogane says:

    So this is how muscle hank looked like in the past?

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