Are Chickens Mammals or Reptiles? | All You Need to Know!

In 2006, a feathered, bird-like dinosaur was discovered in China. Unearthing the fossils shows similarities in genetics, behavior, bones, eggs, and many more. Is the flying dinosaur the ancestor of the modern chickens?

They both fly, but there are several differences that you can spot just by looking at them. If they’re not, is it relevant to relate chickens to mammals or reptiles?

Are chickens mammals or reptiles? Neither. They are birds that belong to class Aves. As you know mammals feed their young milk, but chickens don’t. So, this part makes chickens seemingly related to reptiles as they both lay eggs. However, reptiles are not warm-blooded but instead cold-blooded or ectothermic. 

With simple logic, birds are dinosaurs. Furthermore, dinosaurs and crocodiles are from the same ancestor. But it doesn’t mean that birds are reptiles like crocodiles.

The norm in the past does not apply anymore. The present facts that are featured here are more important.

How Do Biologists Classify Animals?

Biologists use two systems to classify animals. The first one is Linnaean which groups animals without considering their ancestry. Secondly, the phylogenetic system based the classification on the ancestry by determining common characteristics.  

Therapids are animals that are similar to reptiles. They evolved for 320 years and turned into the mammals that exist on earth nowadays. The evolution continues for 120 years in which a group of animals called archosaurs appear.

Taking ancestry as the basis, history shall show you that chickens and crocodiles, like reptiles, are closely associated with each other. It starts with archosaurs which are the ancestors of crocodiles and dinosaurs.

When dinosaur extinction took place 65 million years ago, only the feathered ones were left, and they turned into modern birds.

Are Chickens Reptile Ancestors?

Are Chickens Reptile Ancestors

Chickens reptile ancestors. The reptile-like animals called therapsids evolved into archosaurs which are the ancestors of the feathered dinosaurs that are now modern birds.

Do Mammals Have Fur or Feather?

Do Mammals Have Fur or Feather

Sweating or dissipation of heat and control of body temperature happen through hair and sweat glands. Mammals have furs which are divided into two types of hair. The long and thick fur is called guard hair, while the downy hair is short and soft.

Do Reptiles Have Scales or Feathers?

Do Reptiles Have Scales or Feathers

Reptiles have scales that are dry, tough, and scaly skin. Due to this covering, they can live in dry areas to exclude themselves from predators. Scales have bony plates for added protection, and just like hair; they are composed of keratin.

But don’t compare the scales of the reptile to that of the fish. Their scales are not separated but instead put together in a single sheet. Thus, reptiles like a snake can climb and crawl as they have special scales on their bellies. The skin sheds off periodically.

Do Mammals and Reptiles Lay Egg?

Mammals don’t lay eggs because they have a uterus inside their body that acts like an eggshell. It’s all where the baby develops before birth. However, there are exceptions, and they are echidna or spiny anteater and duck-billed platypus. They’re found in Australia and New Guinea.

These egg-laying mammals are also called monotremes. Since they lay eggs like birds and reptiles, they’re viewed as too primitive for a mammal. Despite that they don’t engage in a live birth, they have mammary glands for milk production.

Reptiles spread in every corner of the world because they reproduce through amniote eggs. This egg is covered by a hard leather-like shell that is rich in calcium carbonate. It’s a protective layer to prevent the embryo from drying out.

With four membranes that cover the embryo, the amniote egg can retain water for further protection and ample room for development. The yolk is intended for nourishment. In the case of mammals, the equivalent of this part is the uterus. As for the nourishment, it’s provided by the placenta.

Chickens and Reptiles Have an Egg Tooth

The completion of the gestation period is necessary among mammals so the babies can travel through the birth canal. This is not an essential process for chickens because the delivery has occurred beforehand. The goal of these fowls is to break the egg open, so the offspring comes out. It can happen through an egg tooth.

An egg tooth is a small bone that hangs on the end part of the chick’s nose. After the chick is released from the egg, this boney tooth falls off. This feature is also possessed by reptiles.

Are Birds and Mammals Warm-Blooded? How About Reptile?

Are Birds and Mammals Warm-Blooded

While birds and reptiles share a common trait in having the egg tooth, birds and mammals see eye to eye as warm-blooded animals. To maintain good health, birds and chickens need to have a body temperature around 105 to 107 degrees Fahrenheit.

The said temperature is too warm for humans and even much warmer for reptiles. Since reptiles are cold-blooded creatures, they thrive at 50 to 104 degrees Fahrenheit.

Chickens feel warm with the plumage but reptiles. The latter crawls not only on land but water as well.

Do Chickens Have Mammary Glands?

Do Chickens Have Mammary Glands

Mammary glands are unique among mammals. Their ridges run across the sides of the mammalian embryo. Mammals in both genders have these glands but disappear among males upon reaching the adolescent stage.

There’s no precise record of the first appearance of mammary glands in the history of evolution. But its existence is connected with milk teeth and teeth replacement which are common among modern mammals, including humans.

Due to the small size and changing of the position of milk teeth, they’re not as efficient and dependable as adult teeth in terms of chewing.

This shortcoming leads to settling with food that doesn’t need chewing, which is milk. Fossil records present that the late therapsids got their baby teeth replaced based on a study about paleoethological inference.

There are glandular tissues in mammary glands for secreting milk. Mammals have different mammary glands, but most species have nipples. No matter what, these features are nowhere to be found among chickens. They don’t have milk to nurse their chicks.

Frequently Asked Questions

Are Chickens Birds?

Chicken are birds, although they have distinct characteristics from the other avians. To support this, they belong to the family Aves in the kingdom Animalia.

They have two wattles under their chins and a comb on the top of their heads. There are various kinds of comb, namely buttercup, cushion, pear, rose, silkie, single, strawberry, and V-shaped. Some birds have them too.

Comparing various birds, the smaller ones breathe faster than their larger counterparts. So, the respiration rate of chickens is higher than that of large birds. A hummingbird is smaller than a chicken. Thus, its breathing rate is higher per minute.

All birds have wings, but some of them can’t fly like kiwi, emu, ostrich, and penguin. You may see chickens that fly short distances or over the fence. This seems to worsen due to domestication.

Chicken breeds developed for meat production can’t fly. They just flap their wings and jump a bit higher. You may see them move rapidly on the ground too.

Related: What Is Chicken? | Information and Facts

Are Chickens a Mammal?

Chickens are not mammals because they have feathers instead of fur and hair. They don’t engage in live birth but lay eggs that are cracked through an egg tooth. Moreover, they don’t have mammary glands, which are common among mammals.

Are Birds Mammals or Reptiles?

Birds are avians that belong to family aves. Therefore, they’re not mammals or reptiles. They neither have hair or furs like mammals nor the scale of reptiles.

Are Chickens Related to T Rex?

North Carolina State University researchers used the protein of T-rex, the first non-avian dinosaur to be involved in tracing the evolution of species. The protein from this dinosaur confirms that it shares a similar ancestry with chickens and ostriches.

Are Chickens and Alligators Related?

Chickens and alligators are related based on the history of evolution. They were both included in the group called archosaurs that lived for 250 million years. Birds and crocodilians have both given life to dinosaurs.


Although some studies and discoveries confirm the relationship of chickens to mammals or reptiles, they’re not enough to categorize them as one family. The Linnaean system backs this up as its pattern doesn’t consider ancestry.

Therefore, chickens are feathered animals or birds that are from the Aves family, which is a different group from mammals and reptiles.

List of Sources

Aves Birds

What Is a Chicken?

Molecular Analysis Confirms T. Rex’s Evolutionary Link to Birds

Analysis of Dinosaur Bone Cells Confirms Ancient Protein Preservation

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