Slimy, scaly, sharp teeth, beady eyes… sharks sure sound like they are reptiles, don’t they? While they may look similar to reptiles, and even slink around in reptilian-like ways, sharks are not actually reptiles.
Are sharks reptiles? At first glance, sharks are confusing. It can be hard to decide exactly what animal group they belong to. Many think they are reptiles because they seem so similar to reptiles like alligators. Others think they are mammals because they are so similar in body shape to whales and dolphins. This may or may not surprise you, but sharks are actually in the fish family.
While sharks do have a backbone, which reptiles have as well, sharks do not breathe air as reptiles do. Sharks open their mouths to take in water, extract the oxygen, and release the rest through the gills on the sides of their heads. They have to be in the water to continue breathing and survive.
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Another way to tell the shark is a fish is to look at its rear fin. On a fish, it is called a “caudal” fin. The caudal fin is vertical and moves side to side, just as all fish rear fins do. This makes the shark a fish, rather than a mammal like a dolphin or a whale. Their tails are horizontal and move up and down.
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Fish vs Reptiles
Although a shark is technically a fish, they do share many similarities with reptiles, which can lead to further confusion.
The skin of a shark and the skin of many reptiles, like snakes and iguanas, is fairly similar. They are both rather rough to the touch (although you probably shouldn’t touch a shark). While reptiles can have scales or rough skin, sharks have scales called “denticles.” These scales are tiny and tooth-shaped and they help the shark swim quickly through the water.
Many reptiles have sharp teeth. Think of snakes with their sharp fangs, or even some lizards with their pointy little teeth. That’s about where the similarities end though. Sharks have incredibly pointy, sharp teeth, yes, but they can have as little as a couple dozen or as many as three thousand. They are also constantly losing and regrowing their teeth, which is something reptiles cannot do.
You may have also heard the term “cold-blooded” in relation to sharks and reptiles. It is true that they are both cold-blooded creatures, further adding to the confusion as to what sharks are. Cold-blooded means these animals rely on their environment to regulate their body temperature. This is unlike birds and mammals who can self regulate their body temperature regardless of what the temperature outside is.
Another key similarity is that both animals can lay eggs. Reptiles tend to lay eggs and bury them in the dirt or sand until the babies are ready to hatch and live on their own. Sharks can lay eggs called “cases” or “purses.” These purses can be spiral-shaped or oval-shaped.
While many sharks do lay eggs, the majority actually give live birth similar to a mammal. The babies stay inside the shark until they are ready to be birthed and then the shark births them, very similar to dolphins and whales.
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The last big similarity between the two animals is that they are carnivores or meat-eaters. Many reptiles eat crickets, mealworms, or even small rodents. Sharks also eat meat, but they get their meat from fish and other small sea creatures.
Sharks are one of the few animals that look like they could fit into multiple categories and leave you scratching your head wondering exactly what these scary creatures are. They swim like a fish, but they are shaped like a whale, but they look and feel like a reptile.
The main thing to remember when trying to identify what category a shark belongs to is to look at their bodies. Their vertical tail that pushes side to side is a caudal fin, which only fish have. Their gills allow them to pull oxygen from the water, which is something else fish do. These will be your easiest clues that the animal you are looking at, in this case, a shark, is actually a fish and not a reptile.