Skull Slushies – What’s inside a dinosaur’s skull?

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?

Skull
Creative Commons License photo credit: Lord_Alex

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……

If you have any questions you would like to ask any of our bloggers or curators, send us an email at blogadmin@hmns.org.

100 Years – 100 Objects: Diplodocus Brain Case

The Houston Museum of Natural Science was founded in 1909 - meaning that the curators of the Houston Museum of Natural Science have been collecting and preserving natural and cultural treasures for a hundred years now. For this yearlong series, our current curators have chosen one hundred exceptional objects from the Museum’s immense storehouse of specimens and artifacts—one for each year of our history. Check back here frequently to learn more about this diverse selection of behind-the-scenes curiosities—we will post the image and description of a new object every few days.

This description is from David Temple, the museum’s curator of paleontology. He’s chosen a selection of objects that represent the most fascinating fossils in the Museum’s collections, that we’ll be sharing here – and at 100.hmns.org/ – throughout the year.

Diplodocus Braincase-original - flippedThis curious item is the rear portion of the braincase from the Museum’s Diplodocus. This portion of the skull was recovered in the original 1902 excavation in Wyoming. The skeleton was studied in 1924, and the information derived from this bone and others indicated enough difference from other species of Diplodocus for classification as a separate subspecies, Diplodocus hayi, making it the holotype specimen and only mounted example of this subspecies in the world.

The braincase is not mounted with the rest of the skeleton. The skull mounted on our skeleton is from the sub-species Diplodocus carnegii. With the expansion and redesign of the Museum’s paleontology hall, the unique braincase will join a remounted Diplodocus on display.

D.hayi closeupOriginally collected by Carl Utterback for the Carnegie Museum in Pittsburg, the dinosaur was overshadowed by the Carnegie’s existing mount of a related subspecies, Diplodocus carnegii. Named for the museum’s principal benefactor, wealthy industrialist Andrew Carnegie, the specimen became the institution’s principal attraction with casts being given as gifts to museums around the world.

Mostly forgotten and relegated to storage at the Carnegie Museum, the dinosaur was acquired by Houston in 1962 with support from the Junior League of Houston. It became Houston’s first dinosaur citizen and was unveiled at HMNS in 1975.

Learn more about the ankylosaur: check out David’s post “Ankylosaur at HMNS: A 40-year mystery solved” Or, wander among prehistoric beasts in the Paleontology Hall, a permanent exhibition at the Houston Museum of Natural Science.

You can see more images of this fascinating artifact – as well as the others we’ve posted so far this year – in the 100 Objects section at 100.hmns.org.