Are Chickens Dinosaurs?

Composite picture: T. rex courtesy of the ever generous public domain - Emile the rooster courtesy of Emile the rooster

Here are some statements for your consideration:

•    “Tyrannosaurus rex was really just a big chicken.”
•    “Chickens are the closest living relative to Tyrannosaurus rex.”
•    “Chickens are directly descended from T. rex.”
•   "Chickens are dinosaurs"

Lately I’ve been running into declarations like these a lot, and I’ve got to say that I wasn’t buying most of them.  None of these statements, it seemed to me, had the ring of truth.  So, I decided it was time to get to the bottom of the dino/chicken thing and find out if there really is some sort of connection between dinosaurs and chickens and if so, what it is. And, after some research, here we go:

“Tyrannosaurus rex was really just a big chicken.”  Seriously?  The most basic comparison shows us that T. rex had “arms” and chickens have wings.  T. rex had a great gaping mouth filled with teeth.  Chickens have beaks.  So just no.  T. rex was definitely not a chicken.

“Chickens are the closest living relative to Tyrannosaurus rex.”  Well, that’s not a false statement, but it’s very misleading.  Here’s an analogy:    Chimps and humans share 96% of the same DNA—there’s obviously a close relationship.  So, to say humans are the closest relative to chimps is a true statement.  To say that all of the citizens of Keokuk, Iowa are the closest relatives to chimps is also true since all those fine people in Keokuk are humans—but it puts a misleading spin on the truth.  It sounds as though people from Keokuk are somehow more closely to chimps than other people are.  Birds and T. rex share some of the same genetic information (nowhere close to 96%, though), so it is true to say that birds and T. rex are related.  It's even true to say that birds are the closest living relative to T. rex, even though they aren't that closely related.  Saying chickens (a subset of birds) and T. rex are closely related takes us back to that misleading spin.  Are chickens closer to T. rex  than all other birds?  Absolutely not! Let me beat you over the head with one more analogy and then I’ll move on.  Think of birds as jellybeans.  Robins are cherry jellybeans, eagles are licorice jellybeans, and chickens are lemon jellybeans.  While there are obvious differences, they all share traits so you can see them as all being members of the same larger group.  T. rex is a Snickers bar.  He is candy but he’s not a jellybean.  There's a relationship but T. rex is not a bird and definitely is not a chicken. 

“Chickens are directly descended from T. rex.”  Are they descended from T. rex at all?  In a word, no.  In the scheme of animal classification, T. rex and all other tyrannosaurs as well as chickens and all other birds all fit into the suborder Theropoda. Theropods are a large and diverse group of animals that have hollow bones and three-toed limbs in common.  One subgroup of therapods is the clade coelurosauria, and all birds and all tyrannosaurs belong to this smaller group as well.  Coelurosaurs have feathers in common.  Yup, tyrannosaurs had feathers—feathers have already been found in two species and scientists suspect they were present somewhere on the bodies of all tyrannosaurs for at least part of their lives.  Within the coelurosauria there are a number of subgroups—one is Tyrannosauroidea that includes T. rex and all of his cousins, another is Maniraptoriformes that includes chickens and all other birds.  These two groups split apart a long, long time ago; waaay back in the Jurassic Period.    Let’s just say that birds and tyrannosaurs are at the same family reunion but on opposite ends of the table, and so T. rex, it turns out, was not grandpaw to chickens—he was more like a shirt-tail relative. 

“Chickens are dinosaurs.”  Pretty much every evolutionary biologist and paleontologist worth their salt long ago came to the conclusion that birds are descended directly from dinosaurs.  And chickens, of course, are birds.  Today it has become generally accepted by scientists that birds are not descended from dinosaurs, but, in fact, are dinosaurs.

Around 66 million years ago there was a catastrophe that affected the whole world—scientists are fairly certain that the actual event was a huge asteroid or comet, perhaps ten miles wide, smashing into the Gulf of Mexico.  In a very short period of time, referred to by scientists as the Cretaceous–Paleogene extinction event, over three quarters of the living species on Earth were wiped out—many insects, mammals, fish, plants, and lizards were suddenly gone.  Almost every large animal disappeared, including T. rex and every one of the other dinosaurs—except for one small group of smallish therapods living on the southern continents—the birds.  Afterwards, the few remaining birds and other animals that survived spread across the world and evolved into the species we have today.  One bird that evolved in Asia was the red junglefowl, and chickens are the domestic version of that bird.

So, there you have it.  Next time you call your chickens “little dinosaurs”, you can be sure that you’re being absolutely correct.  But calling your overly aggressive rooster a T. rex is, well, just taking it a bit too far.

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