Last update:

Are Chickens Mammals or Reptiles?

When you are raising chickens, you may sit back and wonder what they are. Chickens tend to have a lot in common with other animals. For example, you can see a bit of reptilian characteristics when they lock onto you with a single eye or in the scales of their legs. But then chickens have warm blood and don’t need the sun to stay warm. So, are chickens mammals or reptiles? They’re birds!

Here are some characteristics of chickens and other birds to prove that they are of their own species and not mammals or reptiles.

Chickens Are Birds, Not Mammals or Reptiles!

the reptile family tree
Photo credit: Twitter post

What makes a bird a bird? According to the encyclopedia, a bird is a creature with feathers, wings, two legs, and a beak or bill. Moreover, birds tend to be warm-blooded, lay eggs, and have a backbone. Most birds can fly, though there are some birds that cannot, like the penguin.

Birds do have a lot in common with reptiles, being that they descended from them, but they have evolved into a very different class of animal.

Here are some reasons why chickens are neither mammals or reptiles:

Mammals Have Fur or Hair, Birds Have Feathers

You can rule out chickens being mammals right away by their appearance. Most mammals have hair or fur on their bodies. Why, even the whales that swim in the oceans still have hair follicles or even some hair on their bodies to distinguish them from fish! Interestingly, mammals have hair or fur instead of scales because they evolved from something very different from reptiles or birds.

Mammals come from a class of creatures called synapsids, which started popping up around 320-315 million years ago. Meanwhile, birds started evolving around 150 million years ago from the dinosaurs, including the T.Rex.

Reptiles Have Scales, Not Feathers

You could argue that chickens have scales on their legs, but some breeds do not. Birds have feathers covering a large portion of their bodies, while reptiles are covered predominantly in scales. This separates birds from reptiles.

Feathers did not evolve directly from reptilian scales, though that was once the hypothesis. It has been found that the earliest of feathers were not for flying but for insulation — which still holds true — and repelling water.

Birds Do Lay Eggs, But Mammals Do Not

hen laying eggs on nest

Being that both birds and reptiles lay eggs has led many people to believe that chickens are reptiles. But you can’t truly argue that. Look at the platypus, a mammal that lays eggs and has a bill.

The other reason chickens are reptiles is because their egg-laying habits are different. Reptiles, for one, carrying their eggs for longer. The embryo must be at least a third of the way developed before the reptile mama lays a clutch. Afterwards, the eggs hatch in a couple of days. A chicken does not keep the egg in their body for too long. Upon formation, the egg is deposited within a day outside the body then needs 19-21 days of incubation before hatching.

Birds and Mammals Are Warm-Blooded

Birds and mammals are warm-blooded. Reptiles, generally, are not. Furthermore, chickens can regulate their own body temperature with their wattles and combs. If they get too cold, your chickens may even get frostbite. Reptiles need to rely on external heat. When raising backyard chickens, you will notice that they need to stay warm throughout the winter, because they do not hibernate.

To compare, chickens have a body temperature of 105-107 degrees F, which is hotter than humans. Reptiles maintain a core temperature of around 50-104 degrees F. This means they are more comfortable getting both hot and cold, which serves them when they are moving to and from water or shade.

What About the Egg Tooth?

egg tooth

One thing that makes chickens and reptiles very similar is something called an “egg tooth.” Anything that forms within an egg needs to be able to break out of the shell with ease, yes? Well, that’s where the egg tooth comes in. An egg tooth is technically a small projection that is on the beak of a newly hatched chick, bird, or reptile. Once the chick has hatched, the horn will fall off.

Photo credit: ScienceDirect

During incubation, the egg tooth develops quickly, around the seventh day. It takes time for the tooth to become sharp and hard, but about the time the chick is ready to burst from the egg, the tooth is ready. Three days prior to hatching, the chick uses the egg tooth to tear the inner membrane of the egg.

Prior to damaging the inner membrane, the chick is receiving oxygen from pores in the shell. The larger the chick gets, the more oxygen it needs to survive. The egg tooth helps them pop the membrane, allowing for more oxygen to flow through the shell. This is called “internal pipping.”

The next time the chick uses the egg tooth is to make an external pip, which is the first hole puncturing the entire shell. Fascinatingly, birds and reptiles all have muscles specifically for hatching, too. Chicks have enlarged pipping muscles in their necks that spasm as they exit the eggshell. However, because this task is exhausting, the chick needs to sleep for about 8 hours before it can continue on.

Chicks beat against the egg thousands of times before they break free. It may take 5 hours before the chick creates a shell cap. It may take another 40 minutes before the shell cap is free.

All in all, the chick takes about 24-48 hours to escape the confines of the egg. Over the next day, their beak grows strong until the egg tooth breaks off. Sometimes, the egg tooth remains for 4 days, depending on the breed.

You can also see how it looks in action in the video:

But Wait, Reptiles Don’t Have Beaks!

You may think that the fact that birds have beaks is enough to separate them from everything else. Interestingly, reptiles and mammals can also have beaks.

A beak is often made from a hard substance, such as keratin or bone. For example, a turtle’s beak is made of keratin, the same as a parrot’s or woodpecker’s bill. Keratin never stops growing. Even humans and other mammals use keratin to form up features of the body, including hair, fur, nails, hooves, horns, and skin.

Another animal with a beak is the parrot fish, which looks like an aquatic parrot — thus aptly named. However, the beak of a parrot fish is not made of keratin. No, that beak is made with actual bone.

So, while chickens have beaks, and that technically puts them in the bird category, beaks are not unique to birds in the animal kingdom!

These Hollow Bones Belong to Fowl

If you truly want to separate the chicken from the reptiles, take a look at the bones. Birds, including jungle and marine fowl, have a distinct bone structure that enables flight. Hollow bones are an evolution that helps birds maximize their strength despite their weight. While it is posited that dinosaurs had hollow bones, their skeletal structure did not enable flight.

Furthermore, fowl like chickens have air sacs hidden in their bodies to assist with flight or flotation. The air sacs fill and deflate as they breathe. Furthermore, some fowl will have these air sacs in their hollow bones. By adding pressure to the bones, the birds are able to strengthen their bodies without increasing their body weight. Cool, right?

Lastly, we cannot overlook the wishbone. All poultry — chickens, turkeys, ducks, and geese — have wishbones in their chests. Many other birds do not have a wishbone, otherwise known as a fused collarbone.

Are Chickens Really Related to Dinosaurs?

birds place among the dinosaurs
Photo credit: Twitter post

Back in 2008, the Smithsonian magazine released an article stating that the closest living thing to the majestic and terrifying Tyrannosaurus Rex is the humble ostrich and chicken. This has led to some assumptions that chickens are dinosaurs in their own right. The truth is that, yes, chickens are indeed to the mighty dinosaurs that once roamed our planet. However, they are not reptiles nor dinosaurs — not anymore.

Birds did evolve from dinosaurs. The proof of that is as plain as the scientific evidence of feathered dinosaurs. So while birds and reptiles are very closely related, there are differences that make them very distinct these days.

Final Thoughts

Are chickens mammals or reptiles? They are neither! Chickens are a kind of bird, known as land fowl or poultry. Chickens are related to reptiles, but they long ago evolved to be very different from their scaled ancestors. Therefore, why you can call your chickens the descendants of raptors, they are closer to a duck or an eagle than an iguana these days.