Is There a Bone in a Shark’s Body?
Answer:
No. Sharks, like other fish, have skeletons that are made of cartilage. Cartilage is flexible and tough material. It makes the skeleton lighter than bone to help the shark swim faster. Some sharks also have teeth that are shaped like tiny serrated spoons for crushing shellfish shells.
Some sharks have spines made of sharp calcite to protect them from predators.
Did you ever wonder why there are so many fossilized shark teeth, but so few actual fossils of sharks?
There’s a straightforward explanation for it: sharks and their relatives, unlike humans and most other vertebrate animals, don’t have bones in their skeletons.
Their bones are constructed of cartilage, the same material as your nose and ears. It’s less dense and more flexible than bone, but it doesn’t mineralize as well because it doesn’t mineralize as much.
The first thing that distinguishes sharks and their relatives, called class Chondrichthyes (“cartilage fish”), from other fishes, which are known as class Osteichthyes (“bony fishes”), is the fact that they don’t have cartilage.
What exactly is cartilage, and how is it distinct from the bone? You may exhibit the distinction on your own body!
Bend your arm halfway between your wrist and elbow. You can’t. Bone is a pretty sturdy material. Now crinkle your ears and nose for me. That’s cartilage, which is much more flexible than bone!
The denser cartilage of some shark bones is particularly thick, as seen in the vertebrae (which do typically fossilize).
The cartilage that lines the inside of your knee is different from the cartilage in your wrist. Different sections of a shark’s skeleton may have very distinct kinds of cartilage with various structures and functions.
However, the entire skeleton, including the jaws, is composed of cartilage. Chondrocraniums are shark “skulls.”
The toothed whale’s name comes from the word chondr, which is derived from the Greek words for “cartilage.” (Chondrichthyes are composed of cartilage as well.) The root word chondro was used to describe humans who had a chondrocranium in their early development but would lose it.
What about shark teeth? Shark teeth, like ours, are made of hard tissue called dentin (which we Americans call “dentine”), which is calcified.
The thicker, more robust tissue fossils are better. I’m frequently asked at my public lectures if those shark tooth necklaces sold in tourist curio shops all around the world are a conservation danger for sharks.
You’re probably familiar with the word “sabre-toothed,” which refers to sharks that have one or more of their teeth filed down. These aren’t; many are constructed from fossilized shark teeth, which are typically white in color and indicate a freshly dead animal. And dermal denticles (“skin teeth”) that sharks lack are quite toothlike and can be fossilized.
In conclusion, sharks do not have bones.
