Q&A – Inside the Mind of Dinosaurs with Amy Balanoff

When scientists analyzed the first dinosaur fossils around 200 years ago, researchers and the general public assumed these creatures “were slow, dim-witted animals,” says Amy Balanoff, Ph.D., assistant professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine.

Modern tools including digital endocasts, which use the cranial cavity in fossils to determine the size and function of the brain, and digital PET scans, have shown otherwise, Balanoff says.

“Dinosaurs were probably fairly cognitively advanced animals in many respects,” she says. “The brain size of the Velociraptor, which is within the larger group of theropods that gave rise to birds, actually comes close to those of modern birds.”

Tackling myths about the infamous dinosaur predator Tyrannosaurus rex, and exploring questions about its brain size and function, Balanoff and Daniel T. Ksepka, a paleontologist and science curator at the Bruce Museum, co-authored a commentary in Scientific American on what it was like to be a dinosaur.

Studying the brains of dinosaurs helps scientists determine how their modern relatives —birds — evolved, notes Balanoff.

“Birds are dinosaurs,” she says. “A lot of my interest in dinosaurs came from being interested in birds, trying to understand what makes a bird a bird, and how these features evolved.”

Recently, Balanoff and her colleagues analyzed the brains of pigeons to determine which parts are most active during flight. They found that the cerebellum, which coordinates movement, is a crucial component of bird flight.

“We took that information and we looked at where the cerebellum expanded in evolutionary time — which occurred just before the evolution of powered flight,” she says.

We asked Balanoff to tell us how she got started in the field of paleontology, to explain some misconceptions about dinosaurs, and to share some information about the T. rex brain.

Q: What inspired you to write your commentary in Scientific American on what it was like to be a dinosaur?

A: In part, we were replying to a paper that made broad generalizations about the cognitive ability of Tyrannosaurus rex based on the number of neurons in their brains. Their argument was based on their estimate of the brain size of T. rex.

The other researchers estimated that the T. rex brain filled that entire cranial cavity. But it’s actually more complex. Endocasts, which are casts of the cavity that once contained the dinosaur brain, provide a picture of how the brain would have looked during life, but this would also include vascular structures in addition to brain tissue. Essentially, we think they overestimated the brain size and therefore the number of neurons within the brain.

Then we decided to fill in a few other details about T. rex. Research has demonstrated that, compared with birds, extinct dinosaurs tended to have proportionally larger olfactory bulbs, which are the brain structures that help us smell. Based on the size of their olfactory bulbs, researchers have estimated that T. rex had more than 600 olfactory receptor genes, more than almost all modern birds. This tells us that the T. rex could easily sniff out its next meal.

The size and shape of its eye sockets can also tell us something about how well T. rex could see. Although it was unlikely to be nocturnal like some other small dinosaurs, it probably had overlapping visual fields to give it some level of essentially 3D vision.

Q: How did you decide to become an expert on the brains of dinosaurs?

A: A lot of my interest in dinosaurs came from my focus on bird evolution, trying to understand what makes a bird a bird, and how birds evolved. Birds are dinosaurs.

I picked up invaluable skills during my master’s degree program at the University of Texas at Austin. Scientists were beginning to use CT in paleontology, including to look at the brains of extinct animals, and UT was at the forefront of using these techniques. I worked on using CT to reconstruct the embryonic skeleton of an extinct elephant bird that was once found in Madagascar and laid two-gallon-sized eggs.

I then moved to Columbia University to do my Ph.D. with Mark Norell, the former curator of fossil reptiles at the American Museum of Natural History in New York. While I was there, I had access to a huge number of fossil specimens at one of the world's best museums, so I put the skills I had learned at UT together with these amazing specimens to do work on dinosaur neuroanatomy and evolution.

Q: Your commentary in Scientific American addressed some myths about dinosaurs, for example that the T. rex had a small brain. What are some other common dinosaur myths?

A: The first dinosaur fossil was described 200 years ago. Since then, there's been this idea that dinosaurs were slow, dim-witted animals. That idea was largely a product of many dinosaurs’ large body size.

That myth was dispelled in the 1970s with research by Harry Jerison at the University of California, Los Angeles. But his idea that these extinct dinosaurs were smarter than we thought didn’t catch on for a while.

The brain size of T. rex, which is within the larger group of theropods that gave rise to birds, was big, but most of the brain was devoted to senses like smell. Smaller dinosaurs, including Velociraptors and Troodons, had even larger brains compared to their body size, about the same size that we see in some modern birds.

It’s not only that the entire brain is larger, but specific parts of the brain are larger. For example, the relative size of the cerebrum, where many cognitive processes occur, of Velociraptor would be much larger than what you see in modern crocodilians, and in birds as large as an ostrich. Considering the cerebrum size, Velociraptor was probably pretty smart.

Q: Is it true that some dinosaurs may have had feathers?

A: Depending on how you define a feather, these may have actually evolved before dinosaurs. Pterosaurs, an extinct lineage of flying reptiles that originated before dinosaurs, had filamentous appendages in their skin, which very much resembled feathers.

T. rex, undoubtedly, had some type of feathers. T. rex wasn't flying, so they weren't feathers for flight, but they probably served other functions, like thermoregulation.

We see this same pattern with other bird characteristics like a wishbone, which in modern birds helps with flight, but T. rex had a wishbone.

We've also actually found dinosaur fossils where they had been brooding their eggs, sitting on top of a nest of eggs keeping them warm. That’s another bird behavior we see in the fossil record of non-avian dinosaurs.

Q: How has the field of paleontology changed over 200 years?

A: What's really changed is how we observe the fossils. Once we get them back to the lab, we study the fossils in so many more ways than we could before.

For example, CT scans can help us reconstruct the nervous system. We can fill in the brain cavity in digital format, remove bones surrounding that space from the image, and make an endocast. We can then reconstruct how good (or not) their eyesight and hearing were and use this to predict their behavior.

We can also put digital landmarks on bones or endocasts that allow us to capture their shape and compare it with other species. This can help us understand the different functions of these structures.

These methods have been around for the last several decades, which is actually relatively recent in the history of paleontology. Now, we can use newer, more powerful computers to analyze these data. For example, we can now incorporate these data into phylogenetic analyses, which allow us to reconstruct evolutionary relationships and better understand character evolution.

Q: What can dinosaur senses teach us about modern-day animals?

A: The brains of these dinosaurs tell us how modern bird brains evolved. We can look at when, in evolutionary time, different features of the modern bird began to appear.

Using endocasts, we can start to understand the timing of when certain features first appeared and how that correlates with other skeletal characteristics. For example, when brain size increased, did these dinosaurs develop the ability to fly?

It turns out that increased overall brain size does not correlate with flight, but questions like these are important for understanding the evolution of modern species.

My colleagues and I recently published research using PET scanning, which is a technique that allows us to see activity in the brain. We used PET scans to look at what parts of the brain were most active during flight in the pigeon, which turns out to be the cerebellum, an area for motor coordination. We took that information and we looked at where the cerebellum expanded in evolutionary time—which occurred just before the origin of powered flight.

Q: Is there anything I missed?

A: One thing we tried to stress in the Scientific American commentary is that we have a romantic idea of paleontology, but there's so much more to it. We’re using molecular and developmental data to help us understand the evolution and development of the modern body plan. We think of ourselves more as evolutionary biologists in that we're using an element of deep time to understand modern biology, and that sometimes gets lost.