Chickens clucking in the coop certainly don’t look much like the ferocious Tyrannosaurus rexes and velociraptors of Jurassic Park fame. Yet an increasing amount of evidence shows that today’s chickens and their wild junglefowl relatives are in fact dinosaurs.
This idea may seem bizarre at first. But upon examining the evolutionary history and biological traits of birds and dinosaurs, the connections become clear. Let’s take a deeper look at the dinosaur-chicken link.
Birds Are Theropod Dinosaurs
In the late 1800s, scientists first proposed that birds evolved from dinosaurs based on skeletal similarities New dinosaur discoveries in the 1960s and 1970s, like feathered dinosaurs and warm-blooded dinosaurs, blurred the line between dinosaurs and birds.
Yale paleontologist John Ostrom’s work on Deinonychus and Archaeopteryx consolidated the link between theropod dinosaurs and birds. Theropods are a group of mostly carnivorous dinosaurs with hollow bones and three-toed feet. Birds share these traits.
Biologist Richard Prum stated in a 2003 Nature paper that “there remain no major traits that are unique to birds—with the possible exception of powered flight.” Prum argued that birds are simply a lineage of theropod dinosaurs.
While this idea was controversial decades ago, the vast majority of paleontologists now agree that birds are living dinosaurs. So when we see chickens, hawks, or hummingbirds, we are looking at dinosaurs that survived after the rest went extinct.
The Dinosaur Family Tree
The dinosaur family tree is complex, spanning over 160 million years. Dinosaurs like Stegosaurus branched off early from the theropod lineage that led to birds.
Tyrannosaurus rex appeared much later, around 68 million years ago. But it still belonged to the theropod group. T. rex and his relatives are tyrannosauroids, while birds are maniraptorans. Both are theropods but are not closely related.
By 65 million years ago, the dinosaur ranks included primitive birds like Enantiornithes as well as early galliforms, the chickens’ ancestors.
The End of Most Dinosaurs
Everything changed about 66 million years ago when an asteroid struck Earth, causing the Cretaceous-Paleogene extinction event. Three-quarters of plant and animal species went extinct, including famous dinosaurs like Triceratops and T. rex.
Some dinosaurs managed to survive, including a few theropods. Birds were among them. Over time, avian dinosaurs continued evolving into the 10,000+ species we see today. One small galliform evolved into the red junglefowl, the wild ancestor of the domestic chicken.
Examining the Evidence
So what evidence confirms this dinosaur-bird connection?
Fossils – Numerous feathered dinosaur fossils demonstrate how bird-like traits were evolving. Sinosauropteryx, Microraptor, and other feathered dinosaurs cement the link.
Cladistics – Analysis of evolutionary relationships places birds firmly within theropod dinosaurs on the tree of life. Birds and T. rex share a common ancestor.
Similar skeletons – The skeletal structure of birds and theropods is practically identical. Ostriches have the classic S-shaped dinosaur neck.
Behaviors – Behaviors like nest-building, brooding eggs, and parental care are shared by birds and their dinosaur ancestors.
Soft tissues – Preserved protein fibers in dinosaur fossils match those found in chicken collagen. This indicates a close biochemical relationship.
DNA – While no actual dinosaur DNA survives, analyzing bird genes suggests they branched off from other dinosaurs around 150 million years ago.
Alive today – The most compelling evidence that birds are dinosaurs? We can simply look out our windows and see dinosaurs tweeting and pecking at bird feeders. Extinction is relative after all.
Why the Confusion Exists
Given the overwhelming evidence, why does misinformation persist claiming chickens are the closest living relatives of T. rex specifically? Unfortunately, exaggerated media coverage is partly to blame.
In 2007, scientists analyzed collagen protein found in T. rex fossils. They made headlines announcing T. rex collagen was more similar to chicken collagen than other animals.
While true, science journalists wrongly concluded this meant chickens were T. rex’s closest living relative. In reality, it simply showed birds and tyrannosaurs shared common ancestry as theropods. The nuance got lost in translation.
Since then, the oversimplified and incorrect T. rex-chicken connection has spread widely in pop culture through TV shows, books, advertisements, and social media. As is often the case with misinformation, the public latched onto an attractive but inaccurate narrative.
Why It Matters
Understanding that birds are dinosaurs gives us a profound glimpse at evolution in action. Dinosaurs are not really extinct – they surround us in vast, wondrous variety. We can observe their direct descendants up close.
Seeing chickens as dinosaurs provides insight into dinosaur biology, behavior and evolutionary adaptations. It also highlights how evolution progresses in fits and starts, with many branches and dead ends along the way.
So while chickens may not be T. rex’s closest cousins, they offer something even better. They let us look back in time through the lens of descent with modification and witness living dinosaurs firsthand. Cluck on, you glorious theropods.
Are Chickens the Closest Living Relative of T. Rex? No! And Here’s Why They Are Not – Part 1
This scene from a recent streaming series: He and she are sitting in a restaurant. She orders the chicken. Then he cleverly and casually mansplains, “Did you know that chickens are the closest living relative to T. rex?” She is suitably impressed by his command of esoteric information. Then the conversation moves on and the chicken/T. rex fiction becomes just a bit more firmly embedded in the minds of the viewers.
You’ve already run into this arcane untrue factoid somewhere, right? Since I’ve been keeping track, I’ve spotted it in an article about feral chickens in a respected popular science magazine, in a chapter entitled “Amazing True Facts” in a popular chicken book, on the underside of a beverage cap as part of that beverage company’s “True Facts” series, and in about a bazillion other places. If you pause reading this for a few seconds and do a web search on the question “Is the chicken the closest living relative of the T. rex” you’ll get links to a whole plethora of articles affirming the “truth” of that statement. Go ahead and do it! And count them! You’ll see that there are exactly a bazillion!
But after the search you came straight back to this article, right? Good. Welcome back. Now, allow me to take a swing at the question. Are chickens the closest living relative to T. rex? No!
At best, it’s a half-truth.
I mean chickens are birds, okay? And birds, all birds—not just chickens, are more closely related to T. rex than any other currently living animal group. So, it is complicated!
But saying chickens specifically are the closest living relative of T. rex is like saying that Ginny Weasley, specifically, is the closest relative to Ron Weasley. Ginny is Ron’s sister, of course, but she’s no more closely related than ANY of the other Weasley siblings! Does that make sense??
Whew. It’s ok. I’m ok. I’m not hyperventilating. Very much. Maybe I’m a little too invested in this T. rex/chicken issue. A few years ago, I wrote an article about the dino/chicken connection. It has proven to be one the most popular posts on my blog – somewhere between a bazillion and a gazillion people have read it since I first posted it. But ever since I took the time to research and write that article, I’ve been sensitized to the continuing drumbeat repetition of that half-truth “The chicken is the closest living relative to T. rex.” The time has come, I’ve decided, for me to do what I can to set the record straight. And while I’m at it I’ll delve into how this crazy half-truth got started in the first place.
We probably need to start with the fact that birds, all birds, are dinosaurs. Maybe this is old news to you. Or maybe you’re clenching your jaw in disbelief? Well, let’s make that fact a header and start from there.
Practically all scientists are now in complete agreement that birds are living dinosaurs. Many non-scientists are also on board with the idea that we can look out our windows and see dinosaurs at our birdfeeders, then go to our coops and collect dinosaur eggs from our chickens. Other folks are still catching up to that reality – thus the jaw clenching and disbelief. The story of how scientists came to realize that birds are living dinosaurs is too long to neatly fit into this article. But I’ll offer my thumbnail version in the next paragraph.
Scientists first advanced the idea that birds descended from dinosaurs in the late 1800’s—based on the similarity in skeletons. New discoveries that led to revised ideas about dinosaurs, including the discovery of dinosaurs with feathers and the realization that some dinosaurs were warm-blooded, blurred the line between dinosaurs and birds. Work by Yale paleontologist John Ostrom in the 1960’s and 1970’s narrowed the divide between therapod dinosaurs and birds. Biologist Richard Prum, also of Yale, was the first scientist to categorically state, in a 2003 paper in Nature that “birds are a lineage of dinosaurs.” He argued that when one examined the traits of birds and the traits of therapod dinosaurs, that “there remain no major traits that are unique to birds—with the possible exception of powered flight.” And there you have it. Birds are therapod dinosaurs. Many dinosaurs became extinct but not all of them. We share our world with millions of dinosaurs and we see them whenever we see seagulls at the beach, pigeons in the park, or chickens in our coops.
The dinosaur family tree is huge and complex. Dinosaurs first appeared 230 million years ago and lived over millions of years with some dinosaur groups giving rise to new dinosaur groups while other dinosaur lineages became extinct.
T. rex came along late in the dinosaur game. He was thundering through the swamps and forests of North America 66-72 million years ago. Those swamps and forests were also filled with birds, which first appeared 150 million years ago.
T. rex and his tyrannosaur kin were all therapods—a clade of dinosaurs that have hollow bones and three-toed feet in common. Birds are also therapods. Among the various clades of therapods, there are the coelurosaurs, a group of dinosaurs that have feathers in common. Within the coelurosaurs there are a number of subgroups. One is the tyrannosaurs that includes T. rex and all of his cousins. Another is the maniraptoforms that includes birds and other related dinosaurs. We can see that birds and tyrannosaurs are perched on the same branch of the dino family tree. But that branch branches again, and again. As branches do. Birds and tyrannosaurs are on very different branchlets.
One day, 66 million years ago, the world was filled with dinosaurs going about their business. Duck-billed hadrosaurs were grazing on horsetails. Ankylosaurs were chowing on ferns. T. rexes were snacking on hadrosaurs and ankylosaurs. There were avian dinosaurs, too. Most of them were enantiornithes; “opposite birds”, primitive birds with teeth and clawed fingers on their wings. There were paleognaths, ancestors of today’s emus and ostriches. There were galloanserae, progenitors to chickens and ducks. And there were neoaves, ancestors to all other modern birds.
Then the asteroid hit the Earth. Almost all the animals I named in the preceding paragraph died.
The Cretaceous–Paleogene extinction event, most likely caused by a large asteroid plowing into Earth, wiped out three-quarters of all the plant and animal species on the planet. Almost every land animal weighing over 55 pounds (25 kilograms) perished. T. rex’s reign was over. Gone with him were the ankylosaurs, the hadrosaurs, and every other non-avian dinosaur. Many birds died, too. Every one of the diverse enantiornithes were gone. The few remaining birds and other animals that survived spread across the world and evolved into the species we have today. One bird was a small ground-dwelling galliform that looked much like today’s partridge. It is the ancestor of the jungle fowl, which was domesticated to become the chicken.
How are the today’s living dinosaurs, the birds, connected to their extinct cousins? Here’s a rough and abbreviated diagram of all dinosaurs and how they’re connected. I don’t expect you to spend hours poring over this chart. I put it together to make a few points: First, you’ll find both chickens and T. rex on this diagram—because both are dinosaurs. I’ve aided your search with green circles around both. Second, you can see that T. rex and chickens are related. Lines connect their boxes. Third, while they are related, they are not closely related. There’s a lot of lines and other boxes between them! Fourth and most pertinent to the point of this article, I’ve highlighted living species in this diagram with green text. Are chickens the closest living relative to T. rex? Nope. It certainly appears that they are not!
How did the chicken/T. rex misinformation get started? I’ve tracked down the origin! It involves a couple of well-known and respected scientists, an important discovery, some incredible scientific work, and the misreporting of that work by the popular press. Get that scoop in Part 2!
Why go around with a chip on your shoulder when you can have a chick…
REASONS Why Chickens Are Dinosaurs?
FAQ
Is a chicken considered a dinosaur?
While a chicken is not a dinosaur in the sense of being a prehistoric reptile, it is considered a living dinosaur because birds are the direct descendants of theropod dinosaurs. Specifically, they are part of the group Avialae, which evolved from theropod dinosaurs like coelurosaurs.
Do dinosaurs have chicken DNA?
The proteins found in the DNA of the T-Rex were most like those of the chicken. To further their research, the chicken was the first bird to have its genome sequenced. This means that scientists found the particular order of their DNA.
What did a chicken evolve from?
Chickens evolved primarily from the red junglefowl (Gallus gallus) of Southeast Asia.