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!
Well…..
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.
Birds Are Dinosaurs
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.
Chickens, Birds and Tyrannosaurs
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.
The End of (Most of) the Dinosaurs
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.
The Dino Family Tree
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!
So, What’s Up with the T. rex/Chicken Rumor?
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!
