March 25, 2016
Until about 60 million years ago, penguins soared above the ocean. When they lost the ability to fly, their brains took a while to catch up.
UT geological sciences graduate student James Proffitt compared 3-D models of the inside of the earliest-known flightless penguin skull fossil to the brain shapes of modern penguins. This fossil is about 60 million years old — this penguin was probably alive soon after all penguins stopped flying.
He expected to find that flightlessness soon affected the ancient penguin’s brain structure, making it similar to modern penguins. However, this ancient penguin brain was significantly different from those of modern penguins, even though they were both flightless. These differences suggest modern penguin brains may not have evolved until relatively recently, according to Proffitt.
“It seems like ancient penguins have a lot more in common with other close diving relatives than they do with modern penguins,” Proffitt said. “When flightlessness evolved, the changes in the brain that you see in modern penguins don’t show up until much later.”
Even though it couldn’t fly, this 60-million-year-old penguin’s skull is more similar to those of present-day birds that can both dive and fly than to modern flightless penguins. Penguin neurology took a long time to catch up to flightless behavior, according to Paul Scofield, the senior curator of natural history at the Canterbury Museum in New Zealand and co-author of the paper.
“I think this result clarifies that the evolution of penguins was rapid and that not all elements of the body suddenly became perfectly adapted to diving,” Scofield said. “Other studies have shown that the brain’s development lags behind the evolution of the body and this is certainly the case in this species.”
The evolution of bird brains is easier to study than other types of animals because bird skulls are closely fitted to the brain. Proffitt’s work used x-ray computed tomography, or CT scanning, to look inside the fossilized skull and observe the shape of the brain.
Chris Torres, an ecology, evolution and behavior graduate student currently in Antarctica studying bird evolution, also uses this CT scanning method to learn about other types of bird brains from fossils.
“Odd as it may sound, we don’t need brains to study brains anymore,” Torres said. “This has profound implications for what we can learn from fossil record, which preserves hard structures like skulls but not soft tissues like brains. CT has revolutionized the way we study how bird brains evolve.”
Proffit is interested in studying penguin evolution because, according to him, they came from a larger group of birds that both fly and swim, but have since evolved flightlessness.
“They make a really great group to examine this broader evolutionary idea of how animals respond to such a big change in ecology and what happens to the rest of their body,” he said.
There is still a lot of research that scientists need to do to understand the relationship between behavior and brain structure, according to Proffitt.
“I think it’s a complicated question to try and disentangle how locomotion effects neurology,” he said. “That’s more of a nuanced scientific story that isn’t as appealing as a firm answer.”