6 Animals That Are Not Mammals

When we think of animals, it’s easy to picture the common mammals around us, like dogs, cats, and even humans. But the animal kingdom is vast and varied, with many creatures that aren’t mammals at all. These include birds, reptiles, and fish—each group adapted uniquely to their environments, showing incredible diversity in form and function.

However, telling the difference between these different animal families can be confusing. Why don’t birds count as mammals even though they’re warm-blooded? What exactly sets reptiles apart? This can make learning about animals and understanding their roles in nature quite challenging.

In this discussion, we’ll explore the fascinating world of non-mammalian animals. You’ll discover their unique traits, understand how they differ from mammals, and learn to appreciate the incredible variety of life on our planet.

A Guide To Animals That Are Not Mammals

What Is A Mammal

Mammals are warm-blooded creatures that are warm-blooded and have a more developed brain than other creatures. Mammals feed their newborns with milk and they give birth to their young rather than laying eggs.

Typically mammals are covered in hair. Mammals also have a backbone and are referred to as vertebrates, Not every creature is a mammal but humans and many other animals are.

Mammals have well-developed lungs. Mammals that live in the water include whales and dolphins. These animals do not have gills and so they go to the surface of the water to breathe air into their lungs.

Animals that lay eggs,(see also: Animals That Lay Eggs) such as most birds, reptiles, and fish are not mammals.  

Animals That Are Not Mammals

There are other families of animals outside of mammals. The main families include birds, reptiles, and fish, we look at each in detail below. 


Birds are often confused for mammals but they are in fact very different and are referred to as avians. Birds do not have fur, they instead have feathers. Some species also have bristles on their faces or heads which can often look very similar to hair. 

Although birds breathe air, are warm-blooded, and possess vertebrae they are lacking in one main characteristic of mammals, they do not give birth to live young or have the ability to nurse their hatchlings.

Birds lay eggs and some species of chicken can even do so without the intervention of a male. Although birds are often intensely protective of their young they cannot nurse the way mammals do.

One bird that is a point of confusion is the pigeon which creates crop milk to feed its young, which is a substance that is made from protein-rich cells and fat which lines a parent bird’s crop, a pouch in the throat that stores food.

The crop milk is semi-solid and bursting with nutrients. We look at other animals who provide crop milk and other substances for their young below. 


Retiles are almost entirely opposite to mammals. They are cold-blooded creatures that are covered in scales rather than fur. Reptiles lay eggs rather than giving birth to live young.

They also do not have mammary glands so they cannot produce milk or nutrient-enriched substances to feed their young.

Reptiles have continuous growth and have very different skeletal structures to mammals. A reptile has a skull with a very small brain case and a jaw that is formed of several bones.

Reptiles also have teeth that are sharp and are constantly replaced should one fall out. 

A reptile’s limbs emerge from the body horizontally.  Reptiles have a low cognitive ability but are incredible hunters. 

The largest reptiles are reticulated python and saltwater crocodiles which both have the ability to grow as long as 23 feet as adults. The smallest reptile is the nano-chameleon which grows to just 0.53 inches long.  

Reptiles can be found in most hot climates but some species can be found around the world in all places except for Antarctica. 


Although many species of fish are warmblooded they are not mammals, although some species of shark and tuna (Also check out Types Of Tuna) are exceptions to this, Fish do not have certain characteristics associated with mammals, such as limbs, fur, or hair and they also cannot breathe air. 

Fish are covered in scales and have gills that enable them to breathe underwater. Fish also do not give birth to live young, they lay eggs and they also do not have the ability to nurse their young which also separates them from mammals. 

There are certain mammals that often get confused for fish as they spend most of their time in the water, these animals include sea lions, porpoises, whales, and hippopotamuses.

Although these animals can hold their breath for a long time underwater they do still require air to breathe.

Animals That Are Not Mammals But Create Milk 

A Guide To Animals That Are Not Mammals (1)

There are some animals that while they are not mammals still share similarities, such as having the ability to create milk or nutrient-enriched milk-like substances to feed their young.

Below are three animals that feed their young using substances that they create similar to how mammals create milk.

Great White Sharks

The pup of a great white shark grows inside the female’s uterus. Great White Sharks do not have an umbilical cord to feed their young and give them the required nutrients as they grow.

As a result, a milky substance is created in the uterus to help sustain the pup until it is born. 


Both male and female flamingoes create crop milk which they regurgitate into the mouths of their young from birth up to the age of six months old.

Due to the presence of canthaxanthin, which is a red-colored antioxidant, the crop milk is a bright red color.

The crop milk also helps the chicks transform from white to pink. As parents give up the red-colored nutrient during breeding season they become slightly paler and more white in appearance. 

Emperor Penguins

Males have the responsibility of guarding and incubating the mother’s laid eggs during the hard winter months for Antarctica’s emperor penguins. The males also create a fatty liquid enriched with nutrients from their crop. 

When the chicks hatch the males regurgitate the crop milk to feed them. The females have the duty of bringing food for the chicks rather than creating the crop milk.

Final Thoughts

We hope that this piece has given you some insight into the animal kingdom and just how varied it truly is.

Now that you know the difference between mammals and animals that are not animals you will find yourself identifying different species out in the wild and being able to distinguish what family they belong to, whether they are fish, reptiles, birds, or mammals. 


Is a shark a mammal?

No, sharks are not mammals; they are classified as fish. They differ from mammals in several key ways: sharks are cold-blooded, breathe through gills, and have skeletons made of cartilage. Additionally, sharks do not produce milk or nurse their young like mammals do.

What are other animals besides mammals?

Besides mammals, the animal kingdom includes a vast array of creatures like invertebrates—such as sponges, cnidarians, and insects—and vertebrates like fish, birds, reptiles, and amphibians. These groups exhibit diverse adaptations that allow them to live in various environments.

Why are all animals not mammals?

Not all animals are mammals because mammals have specific traits like warm-bloodedness, mammary glands for nursing, and typically giving birth to live young. Other animal classes like reptiles, birds, and fish have different biological features, leading to their classification into various groups distinct from mammals.

Olivia Kepner