Chickens are birds. Everyone knows that. Still with me? Good. But the real question is whether or not “birds” as a group fit best fit into some other, broader classification of the animal kingdom.
Are chickens mammals? No, of course not, as they don’t have mammary glands. Are they reptiles? How could they be? They aren’t scaly lizards or turtles!
Actually, just what are chickens in the grand scheme of things, exactly? Are they mammals?
No, chickens aren’t mammals; they are birds, fowls specifically, but they are also descendants of the reptile group, along with lizards and turtles (because their shared characteristics, such as feet and leg structure, egg-laying methods and the type of scales on their skin).
All this makes them more similar to reptiles than any other animal group.
Chickens also have a shared ancestor with other modern reptiles in the ancient dinosaurs, furthering the shared relationship.
Surprisingly enough, this is a topic that gets people hot, hot, hot! The idea that birds are reptiles, and not some distinct class of animals, has been a hotly debated topic in the scientific community for decades.
But based on modern classification standards which are privy to far more information than older systems invented centuries ago, it looks like the definitive determination is in. Chickens, along with all other birds, are probably best classed as reptiles. Learn more below…
What Makes a Bird a Bird?
Before we go any further, we need to define what a bird is. I know that you know what a bird is, but we need a precise definition, biologically speaking, to further classify what they are and get down to the nitty-gritty of what chickens actually are!
A bird is a warm-blooded, two-legged vertebrate animals with feathers and wings. Birds have beaks or bills instead of teeth, and possess hollow bones to make them light enough for flight (usually).
They also lay eggs with hard shells, and have a unique type of scales on their legs called “scutellae”. Remember the part about scales and eggs, it will be important later!
Birds are warm-blooded animals, known as endotherms. This means they have the ability to regulate their body temperature independently of the environment, meaning they can maintain a constant body temperature that’s usually higher than the environment.
This is done by generating their own internal heat through metabolic processes like digestion.
And there you have it, the basic definition of a bird. Now that we know what makes a bird a bird, let’s get into how they could possibly be considered reptiles.
What Makes a Reptile a Reptile?
Reptiles are cold-blooded vertebrates that generally have scaly skin all over their body and they also lay eggs (though some give birth to live young).
Reptiles generally have typical jaws and teeth, though some have beak-like jaws instead.
Most notably, most reptiles are considered ectotherms, meaning they rely on their environment to regulate their body temperature and that’s why so many reptiles are seen basking in the sun to warm up or retreating into shade or underground to cool down.
However, at this juncture I would ask you to keep in mind that there are already some pretty broad discrepancies in these classifications…
You see, some reptiles give birth to live young (like boa constrictors) and many reptiles do in fact generate their own body heat like endotherms by shivering or moving.
This is important because the old grade-school system of animal classification we learned back in the day was in truth pretty outdated even then. We’ll come back to that, but let’s move on for now…
So, How Could Birds Be Considered Reptiles?
Despite birds being warm-blooded and reptiles cold-blooded, there are still enough similarities between them that some scientists believe adamantly they belong in the same group.
For instance, many of the shared characteristics, such as feet and leg structure, egg-laying methods of reproduction, and the type of scales on their skin, all make them more similar to reptiles than any other animal group.
Likewise, reptiles do in fact possess some traits that, according to the old method of taxonomy, belong to other groups, i.e. the ability to generate body heat, give birth to live young, etc.
The dissonance over these seemingly defining characteristics results from the system of taxonomy used to classify them, one created by Carl Linnaeus way, way back in the mid-18th century, and one that bears his name: Linnaean Taxonomy.
The bottom line is that this system is deeply flawed, and not very informative in light of all the info we’ve learned since his day.
Why Linnaean Taxonomy Leaves Birds in the Wrong Box
Linnaean Taxonomy is a system of biological classification that was developed by Carl Linnaeus in the 1700s.
This system organizes all living organisms into hierarchical groups based on shared physical traits, starting with the broadest categories (kingdom, phylum, class) and working down to ever narrower taxonomic divisions (order, family, genus and species).
Most of us are familiar with this system, yes? Or it at least rings a bell? Good, but, what’s the issue? Unfortunately, this system has a major shortfall; organisms were categorized only according to their known traits.
This practice proved useful for organization purposes, but could not inform you of anything about the category aside from what you already knew!
But so many of the “Linnean” names have been used for centuries, they have an almost glacial permanence to them; it is necessary to adjust these categories so they are up-to-date with today’s knowledge on shared ancestry but doing so is maddeningly difficult. This has left birds stuck in a sort of taxonomical limbo
The Case that Chickens are Reptiles
Today, we know that an animal group consists of its ancestor and all of its known descendants: All modern reptiles share common ancestors. That very ancestor is one that birds share, too! I am of course referring to the dinosaurs.
In light of this fact, some have proposed that chickens be rightly considered part of the reptile family. The genes don’t lie: the shared physical characteristics are still obviously apparent.
Unfortunately, this isn’t a good enough argument in the eyes of some professional and amateur taxonomists; they argue that chicken’s unique adaptations such as its feathered wings somehow disqualify them from being considered a reptile.
I think these arguments are nothing more than a thumbing of the nose in the face of unassailable evidence, and I am sure you can see where I’m going with this: Chickens are in fact reptiles, end of story!
And if someone thinks they aren’t, well, don’t take my word for it. Clint Laidlaw, PhD, is a well-known expert in the field and makes a great case for exactly this in a short video:
So, the next time someone asks about your chickens, be sure to tell them all about your reptiles and their neat dinosaur ancestors!
Tom has lived and worked on farms and homesteads from the Carolinas to Kentucky and beyond. He is passionate about helping people prepare for tough times by embracing lifestyles of self-sufficiency.