I’ve seen many debates over whether or not chickens are mammals or reptiles. They do share some common characteristics with both mammals and reptiles, so it can be a little confusing.
The proper answer is; technically speaking, chickens are neither mammals nor reptiles. They are birds, and further classified as a fowl as fowls are birds kept for meat or eggs.
Here is a closer look at some of the physical and anatomical characteristics of chickens that demonstrate why they are neither reptiles nor mammals:
Chickens Have Feathers - Mammals Have Hair or Fur
One of the main characteristics that distinguish birds from mammals is that birds have feathers, while mammals have hair or fur.
According to Inverse.com, this is because mammals and birds evolved from very different groups of animals.
Mammals evolved from synapsids, between 320-315 million years ago. While birds evolved from dinosaurs, like the T.Rex around 150 million years ago.
Feathers also perform some very different functions from hair. Most obviously giving birds the ability to fly.
Chickens are not the most flighty of birds though. They’ve become a little heavy as they’ve been selectively bred to produce more meat over the years.
Reptiles Have Scales, Not Feathers
Reptiles have scales, so they’re different from mammals and birds. Scales are tough and help to protect reptiles from predators, while also giving a lot of reptiles the ability to be in both land and water.
Both Birds and Reptiles Lay Eggs - Mammals Do Not
The fact that both chickens and reptiles lay eggs is enough for some people to think that chickens are reptiles.
But this is not the case. There are also some differences between how chickens and reptiles lay eggs.
The main difference is that egg-laying reptiles carry their eggs a lot longer than chickens. They typically lay their eggs once the embryo is nearly one-third developed.
After laying their eggs, they will typically hatch within a few days. While a chicken’s egg needs around 21 days to develop and hatch once it’s been laid.
Generally speaking, mammals do not lay eggs at all. According to ScientificAmerican, there are just two egg-laying mammals on the planet; the echidna and the duck-billed platypus.
Chickens and Reptiles Have an Egg Tooth
Something else both chickens and reptiles have in common is what’s called an “egg tooth”.
I wrote about what egg teeth are in more detail here. Basically, any animal that develops in an egg needs a way to break out.
Baby chicks, and as far as I can tell most reptiles that break out of shells have an egg tooth. For chicks, this is a hard tooth-like growth on the tip of their beaks.
These hard growths tend to fall off shortly after they’ve broken free from the shell as it has served its purpose.
Mammals do not have an egg tooth. They they have no need for one as they do not break out of eggs.
Birds and Mammals Are Warm-Blooded - Reptiles Are Not
Just when it was starting to look like chickens have more in common with reptiles than mammals - both chickens and mammals are warm-blooded while reptiles are cold-blooded.
Chickens need to stay warm to keep healthy. Their regular operating temperature is between 105-107 degrees F.
This is a little warmer than us, and a lot warmer than reptiles. Most reptiles operate at around 50-104 degrees F, they’re much more comfortable with a lower temperature.
Hence why chickens have a nice plumage to help keep them warm. While reptiles are at home slithering or crawling around in and out of water.
Related - Here’s why you should keep chickens dry when it’s raining.
Mammals Have Mammary Glands - Chickens Do Not
One of the main characteristics of mammals and the reason why they are called mammals is that they have mammary glands.
Mammary glands are organs that produce milk for the sustenance of mammals’ young. Female mammals have these glands and nurse their young.
Chickens do not have these glands, and neither do reptiles. Therefore neither of these classes are able to produce milk and nurse their young
Some Frequently Asked Questions
Are Chickens a Mammal?
No, chickens are not mammals. I covered most of the reasons why chickens are not mammals above. The main differences being;
- They have feathers, not fur or hair
- They lay eggs
- They do not have mammary glands
Are Birds Mammals or Reptiles?
Birds are neither mammals nor reptiles, despite sharing some characteristics with each class. Birds are their own order, of which chickens are classified as fowls.
There are five main classes of animals under the phylum Chordata; birds, mammals, reptiles, amphibians, and fish.
What Animal Class Is a Chicken?
The scientific classification of chickens is:
Kingdom - Animalia
Phylum - Chordata
Class - Aves
Order - Galliformes
Species - Gallus
Don’t feel bad if you thought chickens were classified as either reptiles or mammals.
As you can see from the above comparisons, they share some characteristics with both orders and the lines can get blurred.
At the same time, chickens also have some unique features that demonstrate they are birds. More accurately fowls.
Now you are armed with plenty of new trivia and information to impress your friends!
Related - Are roosters mammals? Further explanation and examination.
Image credits - Photos by Nguyen Tuan, torstensimon, and Tomasz Proszek on Pixabay
Why do mammals have fur not feathers? - Inverse.com
Why Do Egg-Laying Mammals Still Exist? - ScientificAmerican.com