If you spend enough time watching Shark Week or reading about the oceans, you’ve probably wondered are sharks mammals. These predators can be found throughout the world’s oceans and range in size from the tiny Dwarf Lanternshark at 7.9 inches long to the Whale Shark, which can get to around 60 feet long.

Are Sharks Mammals?

Sharks spend time cruising beneath the waves and look an awful lot like fish, but so do whales and dolphins, which are mammals. So, are sharks fish or mammals? Sharks are fish and are different from aquatic mammals in a variety of different ways.

For starters, the vast majority of sharks are cold-blooded or ectotherms like fish, although there are some shark exceptions to this, such as the Great White Shark, which is partially warm-blooded. Mammals, on the other hand, including whales and dolphins, are all warm-blooded. The other term for this is endothermic. They can control their body temperature through a variety of mechanisms, while the body temperature of most sharks is determined by their surroundings.

Shark Eggs. Wait, Do Sharks Lay Eggs?

Another feature that separates sharks from most mammals is that many sharks lay eggs. The only mammals that lay eggs are the platypus and echidna. When you are walking along the beach, you might find an object referred to as a mermaid’s purse. This is a case that holds the eggs of some sharks and rays. 

Some sharks don’t hold fast to this rule. Certain species have live young. In extreme cases, the female shark has eggs that hatch internally, and the young battle for survival, with only one or two defeating their siblings and able to be born.

Do Sharks Produce Milk?

One of the hallmarks of mammals is that they produce milk from mammary glands, which is where the term “mammal” comes from. Sharks do not, as a rule, produce milk, and neither do other species of fish. Several species of sharks produce a substance called uterine milk from the uterus, which can nourish the young of the species, but they don’t consume it via mammary glands, and it is very different from mammalian milk.

Hairy Sharks?

Another defining feature of mammals is that they are generally covered in fur or body hair. Even whales have hair, although they generally only have a small amount of it. In mammals, this fur or hair helps them to regulate their body temperature.

On the other hand, sharks have no hair. They are covered in a rough layer of scales that can make their skin feel like leather. Fish also lack hair and are covered in scales.

Take a Deep Breath!

Like fish, sharks breathe by using gills. These specialized aquatic organs allow these animals to have gas exchange while underwater. In sharks, gills can be quite large and need to be supported by the large frame of some of these sharks, especially huge ones like Whale Sharks. Sharks and other fish take in a mouthful of water and pass it over their gills, where gas exchange occurs and their body picks up oxygen. They release the water back out the gill slits.

Mammals breathe with lungs. If you’ve ever been on a dolphin watching trip or whale watching boat cruise, you have probably seen dolphins or whales surface. Many times when this occurs, they are taking a big breath before going back under the water. They use their blowholes to breathe, which connects to their lungs. Unlike us, these mammals can hold their breath for extended periods of times. But since sharks aren’t mammals, they don’t need to come to the surface and take a big breath of air before going back under the water.

Do Sharks Have a Skeleton?

Sharks have a skeleton, but it’s very different from the skeleton that you or I have. They have a cartilaginous skeleton, so instead of a hard, bony support structure, their skeleton is a little more flexible.

While many mammals have cartilage in parts of their body (think about the cartilage in your ears and nose), the main skeleton is a hard structure made out of bone. In fact, all mammals have three middle ear bones. Sharks don’t have these bones (because they don’t have any bones), so they are not mammals.

Check Out that Tail

Another way to tell sharks are fish is the orientation of their tail. Marine mammals have a tail that is oriented horizontally, while fish have a tail that is vertical. Sharks also have a vertical tail orientation, relating them to fish.

In Summary

Sharks may seem an awful lot like mammals, but they’re definitely fish, so now you know if sharks are fish or mammals. They share much more in common with fish than they do with mammals. So the next time someone asks you are sharks mammals, you can tell them the answer: no, they are fish.