Virtual Lab: Tyrannosaurus Rex Brain

Recommended Reading

Scientists create detailed map of dinosaur brain, Science, theguardian.com

Witmer Lab, Perspectives

Advanced Reading

Witmer and Ridgely, Anatomical Record: Description of T. Rex endocasts.

Assignment Introduction

Just how intelligent were dinosaurs? How can we figure out intelligence of a creature has been extinct for millions of years? One way is by looking at the structure of its brain. Although no one has ever seen a dinosaur brain we can try to infer its structure by doing something which is known as a skull endocast. What an endocast is, is essentially a three-dimensional model of the inside space of the skull, also known as a braincase. This is a space where the brain normally goes. The cool thing is that we don't need to actually do a cast to look at the internal structure of the brain case. In fact, we can perform a CT scan of the fossilized skull and use a computer to model the internal structure of the skull. This lets us create a fairly good image of what the brain of the dinosaur would've looked like. For example, look at the endocast of this Tyrannosaurus Rex’s brain performed by the Witmer lab in Ohio University. Does it seem familiar? 

Endocast of Tyrannosaur brain. Scale bar is 4 cm.

Source: Witmer and Ridgely, 2009, The Anatomical Record

Here is the same brain within the context of the whole skull:

Even though T. Rex had a huge head, you can see that the brain case is actually very small relative to the size of the skull. In fact a lot of the skull is mostly the jaw and sinuses. The sinuses are where the olfactory epithelium used to be which is used to sense odor. Thus, we can infer that the sense of smell was very important for this dinosaur. From here we would predict that the olfactory areas of the T. Rex brain would also be relatively large. Take a look at this animation, showing the skull, the sinuses and the endocast (brain):

So let's go back and take a close look at the brain, do you recognize some brain regions? The big structures up front are the olfactory bulbs (labelled ob) and nearby are the cerebral hemispheres (cer). Other structures that we’re used to seeing such as the optic tectum or cerebellum are difficult to infer and likely were small. The yellow branches at the bottom are the cranial nerves which carry sensory information from the the head to the brainstem and the red squiggly thing is the vestibular labyrinth, which controls the dinosaur’s sense of balance. Overall, the forebrain of the T. Rex is about 2 inches across and 4 inches long. Not very big!

What else can we say about this brain? While it is not very big relative to brains of mammals, it is fairly large relative to brains of other dinosaurs. For example this brain from the sauropod Ampelosaurus is just about the size of a walnut (shown for comparison). This makes sense since T-Rex’s were carnivores and carnivores tend to have bigger brains that allow them to hunt.

If you remember, we recently talked about the encephalization quotient, which is a measure that compares brain and body siuze and somewhat correlates with the intelligence of an organism. This EQ measure is problematic for reptiles, birds and other non-mammalian vertebrates since the relationship between body size and brain varies greatly among species. That said, if we make an adjustment for this and compare T-Rex’s EQ with that of an alligator, the T-Rex’s EQ is between 1 and 2, which is about twice as much as for a large alligator. Does this mean that Tyrannosaurus was smarter than a gator? Not necessarily, at most we can say they are in the same ballpark. 

Perhaps a more useful approach is to compare the function organization of dinosaur brains with the brains of crocodiles and birds. In terms of evolution, dinosaurs evolved after crocodiles and then birds evolved from dinosaurs, so it would make sense that a dinosaur brain would look something like a mix between a crocodile brain and a bird brain. In a recent study, Erich Jarvis and his colleagues at Duke University made functional maps of the brains of birds and the brains of crocodiles. Using special genetic labeling techniques, they were able make functional maps of the various brain regions involved in processing sensory information and in generating vocalizations (or sounds). Then, to get the map of the dinosaur brain, the scientists simply merged that brain maps of alligators and birds. They then took this map and superimposed it on an endocast of the T-Rex’s brain.

Source: Erich Jarvis, Chun-Chun Chen, Duke University

The dinosaur’s cerebrum contains six regions. One of them, the mesopallium, is involved in complex behaviors and processing. This is the same area that is involved in learning and generating songs in songbirds, suggesting that it is technically possible that T-Rex may have used this region to communicate with other members of its species. By comparing the different brain regions in animals that are less evolved and more evolved than dinosaurs, we can begin to infer a little bit about how dinosaurs’ brains worked. What is also remarkable, is that even though dinosaurs have been extinct for hundreds of millions of years, we can still recognize structures in their brains that living animals still have. The basic organization of the vertebrate nervous system has been maintained for millions and millions of years!

Cool Resource: If you want to explore endocasts further, this page from the Witmer lab has a bunch of interactive 3D endocasts and movies from all sorts of species, living and extinct, from humans, to sabertooth tigers to dinosaurs.

 Instructions:

Now that you have learned how you can use comparative neuroanatomy to learn a little bit about brain function in extinct animals, you will now apply your skills to determine brain function in fictional creatures! For this assignment, you will generate a blog post in which you detail the brain anatomy and organization of any creature you could possibly imagine.

1. Choose a fictional character or make up your own creature. Use a cartoon character, your favorite Pokémon, or your favorite movie monster.

2. Consider the different sensory abilities that your creature has, as well as the different types of behavior is required to do. Then, based on what you’ve learned about brain anatomy and brain organization, design this creature’s nervous system. Think about which parts of the brain would be the largest, and which should be the smallest. Think about what sensory organs your creature would have. And think about what types of brain structure you would need to support its behavior. So for example, if I were to pick Bugs Bunny, his brain would likely have the shape of a rabbit brain, except that since he walks upright, the spinal cord and brainstem would be at a right angle from the forebrain, sort of like in humans, instead of straight back.  Certain regions of the forebrain involved in generating language would be much larger than in a regular rabbit, as would areas involved in social cognition such as the prefrontal cortex. Unlike a normal rabbit, Bugs Bunny's brain would also have a significantly large representation of its hands in its somatosensory and motor cortex. Be creative! Feel free to include drawings, diagrams or anything you would like us to know about your creature. Or just simply write a descriptive set of paragraphs.

3. Once your project is complete, click your section's blog in the navigation column on the left and upload all your material including pictures and text into a new blog post. Be sure to include an image of your creature.

4. Comment on two other blog posts from your peers and reply to any comments on yours.

5. Lastly, return to this page, click '+Submit Assignment' and enter the url of the blog containing your work.