Do sharks have bones? Here's what's inside a shark
No, sharks don't have a single bone in their bodies. Their whole skeleton is made of cartilage, the same bendy stuff that shapes your ears and the tip of your nose. The only hard parts that aren't cartilage are their teeth.
Sounds like a weakness, right? A top ocean predator held together by ear material. It turns out to be one of the main reasons sharks are so good at being sharks.
Why cartilage instead of bone?
Cartilage is roughly half as dense as bone. A lighter skeleton means less weight to push through the water, and a more flexible one lets a shark bend and turn tighter than you'd expect from something that size.
Sharks, rays and skates all belong to the same group, the cartilaginous fishes. Scientists think their ancestors may actually have had bonier skeletons and swapped them for cartilage because it worked better in the water.
How does a shark float without bones or a swim bladder?
Most bony fish have a swim bladder, a gas-filled pouch that keeps them from sinking. Sharks don't. They stay up with two tricks instead: a light cartilage skeleton, and a huge liver packed with oil. Oil is lighter than seawater, so the liver works a bit like a built-in float.
If it's all cartilage, how do they bite so hard?
Not all shark cartilage is soft. Over time, calcium salts from their food get deposited in the cartilage of the jaw, the spine and the case around the brain, which makes those parts much stiffer. It still isn't bone, but it's tough enough to take the force of a bite.
The jaw has another trick too. A shark's upper jaw isn't fused to its skull, so it can push forward and open extremely wide when it bites.
Why are shark fossils almost always teeth?
Cartilage breaks down long before it can fossilise, so full shark skeletons almost never survive. Teeth do. That's why most of what we know about ancient sharks comes from teeth, including Megalodon, whose teeth could reach about 7 inches (18 cm) long. We've never found a complete Megalodon skeleton.
The shark "fact" almost everyone gets wrong
You've probably heard that a shark can smell a single drop of blood from a mile away. It can't. The real range is closer to a quarter of a mile, and at their most sensitive, sharks pick up about one drop of blood in a small swimming pool. Still very impressive. Just not a mile.
Quick quiz: 3 questions from the Sharks Trail
These come straight from the first Sharks Trail in Sleevr. Tap each one to check your answer.
1. What is a shark's skeleton made of: calcium, marrow or cartilage?
Cartilage. It makes sharks lighter and more flexible in the water.
2. Which is the largest shark species: the great white, the hammerhead or the whale shark?
The whale shark. It's a gentle filter feeder that can grow over 40 feet long.
3. Sharks have been around for more than 100, 200 or 400 million years?
400 million years. That makes sharks older than the dinosaurs.
Sources: Natural History Museum, "Do sharks have bones?" · BBC Science Focus, "How do sharks smell blood underwater?"
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