There are at least 500 known species of sharks living across all the world’s oceans. Here are some surprising facts about them:

1. They don’t have bones
Sharks filter oxygen from the water through their gills. They belong to a group of fish called elasmobranchs, which means their bodies are made of cartilage instead of bone—similar to the tissue in our noses and ears. Rays and sawfish also belong to this group. Their cartilage skeletons are much lighter than bone, and their large, oil-filled livers help them float.

Despite lacking bones, sharks can still fossilize. As they grow, many sharks deposit calcium salts in their skeletons, making them stronger. Dried shark jaws feel heavy and solid, much like bone. These minerals, along with the enamel in their teeth, allow both skeletons and teeth to fossilize.

2. Most sharks have good vision
Sharks can see well in low-light conditions and can distinguish between colors. A reflective layer of tissue at the back of their eyes helps them see clearly in the dark.

3. They have special electricity sensors
Tiny black dots near their noses, eyes, and mouths are special organs that detect electromagnetic fields and temperature changes in the oceans.

4. Their skin feels like sandpaper
Shark skin has the texture of sandpaper because it’s covered in tiny tooth-like structures called dermal denticles. These scales point toward the tail, reducing drag and helping them swim efficiently.

5. They can be put into a trance
When a shark is flipped onto its back, it enters a trance-like state called tonic immobility. Scientists often use this technique when studying species like sawfish underwater.

6. They’ve existed for hundreds of millions of years
Fossilized shark scales found in Australia and the U.S. suggest that sharks first appeared about 455 million years ago.

7. Scientists estimate their age by counting growth rings in vertebrae
Shark vertebrae have alternating transparent and opaque rings, similar to tree rings. For instance, 10 pairs of rings indicate a 10-year-old shark. However, newer research shows this method isn’t always reliable, so scientists must study each species carefully to determine age accurately.

8. Blue sharks really are blue
Blue sharks have a vivid blue color on their backs and white underbellies. Mako and porbeagle sharks are also blue, though less brightly. Most other sharks are brown, olive, or gray.

9. Whale sharks have unique spot patterns—like fingerprints
Whale sharks, the largest fish in the oceans, can grow up to 12.2 meters long and weigh as much as 40 tons. The second-largest, the basking shark, can reach 12 meters and weigh over 5 tons. Each whale shark has a unique spot pattern, just like a fingerprint.

10. Not all sharks have the same teeth
Mako sharks have very sharp teeth, while great white sharks have triangular, serrated ones. A single sand tiger shark can go through around 35,000 teeth in its lifetime.

11. Sharks reproduce in different ways
Sharks show great diversity in reproduction. Some lay eggs, while others give live birth. Egg-laying species release egg cases that develop outside the mother’s body. Remarkably, there are also recorded cases of female sharks reproducing through parthenogenesis—giving birth without a male.