We get so many great questions through our blog, and every now and then we can turn those responses into a blog post. One our readers favorite posts is “What would YOU ask a paleontologist?”
Last week we got this question from Britt:
“ok so, if dinosaurs, for the most part had tiny little brains, and giant heads, what filled up the rest of their head if not brain? like some kind of brain slushie or what?”
Dr. Bakker, curator of paleontology here at the museum wrote this in response:
Skull Slushies – What’s inside a dinosaur’s skull?
Darn good question. You’re asking about the fundamental architecture of a vertebrate head. And to understand the skull, you must discover that there are really two skulls in your head, one inside the other.
The outer skull is a shell of bone that makes your eye-socket, the hole for your nostrils, your cheek and upper jaw with its row of teeth. Same for T. rex or a Triceratops or a cocker spaniel……. Komodo Dragon, man-eating Nile Crocodile, etc., etc.
Inside the outer shell of bone is the cranial inner sanctum – the braincase. Yep – the braincase houses the brain. There are holes in the braincase to let out nerves and sense organs. The eyeball really is a big nerve. It comes out a hole in the front of the braincase and then goes into the eyesocket. The nerve for your sense of hearing goes out a hole in the braincase located further aft. This auditory nerve goes out sideways and ends up inside a ball of bone at the base of your ear.
The spinal cord is a huge bundle of nerves that goes out the biggest hole – we label it the foramen magnum. The spinal cord continues to the rear through holes in the vertebrae.
The outer skull and the braincase are attached to each other a couple of places at the top, sides and rear of the head.
Brains and only brains fill the braincase. Fine. Now what is between the outer skull and the braincase? Slushies? Packing peanuts? Old newspapers wadded up? Receipts from Buckey’s?
Nope. More important stuff – muscles. The muscles you use for chewing are packed between the outer skull and braincase. Try this: get some tasty beef jerky and chew. Put your fore-finger on the side of your head, just behind your eye-socket. There’s a hole in the outer skull here. You can feel your jaw muscle bulging as it contracts each time you chew.
That chewing muscle is your temporal muscle. The hole in your outer skull is a temporal fenestra (temporal “window”). Now trot out to our dinosaur display and check out the T. rex. skull. There are lots of holes in the outer skull. The tall oval hole is for the eye. To the rear it has a hole shaped like a w turned on edge. That’s a temporal fenestra. Look through this hole, You’ll see the braincase.
In animals with mid-sized brains, like T. rex, there’s a lot of space between the braincase and the outer skull at the temporal window. All the space was filled with muscles. So the jaw muscles were thick and strong.
We humans are the opposite of a rex. We have a giant, bulgy braincase chock full of brain. We’re the thinkiest species on land (porpoises give us competition in water). But we are wussies when it comes to chewing. There’s only a thin space between braincase and outer skull. Check out a human skull. It’s humbling. We just can’t chew hard.
Now, every time you see a skull on exhibit, try to judge how much room there was for chewing muscle between the outer skull and the braincase. Hyenas are particularly intriguing……
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