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Did dinosaurs have a separate brain in their behinds?

Dear Cecil:

I've wondered about this for years, ever since I heard it in the third grade from Steve Revoi. He said brontosauri had a brain in their butt. Is this true? What did it control? Was it part of the central nervous system or an entity unto itself? Did it have angst or did it feel integrated into the whole being of the brontosaurus? How about its sex life? As you can tell, I am very curious about this topic.

Ruth M., Alhambra, California

Illustration by Slug Signorino

Cecil replies:

Your feelings are understandable, Ruth; there’s no question that the phenomenon of creatures with their brains up their butts has acquired a certain desperate relevance today. But let’s start with dinosaurs. Actually, it wasn’t the brontosaurus that supposedly had two brains, it was the stegosaurus, the one with the spikes running up and down its back. Archaeologists found there was a big enlargement in the stegosaurus’s spinal cord at the point where it passed through the pelvis. Since the stegosaurus had a pretty poor excuse for a brain in its head–the thing was about the size of a walnut, only 1/20th the size of the mysterious butt organ–speculation arose that the giant reptile needed some auxiliary gray matter to mind its rump while the forward brain handled business up front.

Naturally, this idea provoked a certain amount of merriment amongst the more disreputable elements of the popular press. In 1912, columnist Bert Taylor of the Chicago Tribune penned the following ode on the subject:

Behold the mighty dinosaur
Famous in prehistoric lore,
Not only for his power and strength
But for his intellectual length.
You will observe by these remains
The creature had two sets of brains —
One in his head (the usual place),
The other in his spinal base.
Thus he could reason “A priori”
As well as “A posteriori.”
No problem bothered him a bit
He made both head and tail of it.
So wise was he, so wise and solemn,
Each thought filled just a spinal column.
If one brain found the pressure strong
It passed a few ideas along.
If something slipped his forward mind
‘Twas rescued by the one behind.
And if in error he was caught
He had a saving afterthought.
As he thought twice before he spoke
He had no judgment to revoke.
Thus he could think without congestion
Upon both sides of every question.
Oh, gaze upon this model beast;
Defunct ten million years at least.

Alas, it was too good to be true. Later scholars decided that the putative afterbrain was just a neural junction where a lot of nerves happened to enter the spinal cord. Such junctions are found in many lizards, as well as in the ostrich. Dinosaurs may have been stupid, but they didn’t suffer from multiple personalities.

Cecil Adams

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