Penguins have developed a very efficient and unique way of moving both on land and in the water but lost their ability to fly. This loss of flight ability, however, did not change their brain structures. A research team has found evidence in a 60-million-year old fossil that the brains of early penguins resembled the brains of modern birds which still fly and dive.

Penguins lost their ability to fly because their food source in the marine environment was easier to catch when adapted to the water, i.e. being heavier and hydrodynamically shaped. Plus, no pressure by land predators in their breeding grounds might have added to the loss of flight Picture: Michael Wenger
Penguins lost their ability to fly because their food source in the marine environment was easier to catch when adapted to the water, i.e. being heavier and hydrodynamically shaped. Plus, no pressure by land predators in their breeding grounds might have added to the loss of flight Picture: Michael Wenger

Losing the ability to fly gave ancient penguins their unique locomotion style. But leaving the sky behind didn't cause major changes in their brain structure, researchers from The University of Texas at Austin suggest after examining the skull of the oldest known penguin fossil. The findings were published in the Journal of Anatomy in February. "What this seems to indicate is that becoming larger, losing flight and becoming a wing-propelled diver does not necessarily change the [brain] anatomy quickly," said James Proffitt, a graduate student at the university's Jackson School of Geosciences who led the research. "The way the modern penguin brain looks doesn't show up until millions and millions of years later." Proffitt conducted the research with Julia Clarke, a professor in the Jackson School's Department of Geological Sciences, and Paul Scofield, the senior curator of Natural History at the Canterbury Museum in Christchurch, New Zealand, where the skull fossil is from.

The fossilized skull (left) and a 3D-model of the endocast (right). Results of the scan show that the size of the endocast is comparable of modern birds like loons and divers which both fly and dive. Still, some of the structures are also found in modern penguin species. Picture: James Proffitt
The fossilized skull (left) and a 3D-model of the endocast (right). Results of the scan show that the size of the endocast is comparable of modern birds like loons and divers which both fly and dive. Still, some of the structures are also found in modern penguin species. Picture: James Proffitt

The skull is from a penguin that lived in New Zealand over 60 million years ago during the Paleocene epoch. According to Proffitt, it likely lived much like penguins today. But while today's penguins have been diving instead of flying for tens of millions of years, the change was relatively new for the ancient penguin. "It's the oldest [penguin] following pretty closely after the loss of flight and the evolution of flightless wing-propelled diving that we know of," Proffitt said. The shape of bird skulls is influenced by the structure of the brain. To learn about early penguin brain anatomy, Proffitt used X-ray CT-scanning to digitally capture fine features of the skull's anatomy, and then used computer modeling software to create a digital mold of the brain, called an endocast.

Waimanu means „waterbird” in Maori and describes a group of early penguins. They lived around 60 million years ago in New Zealand and are considered the earliest flightless member of the penguin order. Picture: Nobe Tamura
Waimanu means „waterbird” in Maori and describes a group of early penguins. They lived around 60 million years ago in New Zealand and are considered the earliest flightless member of the penguin order. Picture: Nobe Tamura

The researchers thought that loss of flight would impact brain structure--making the brains of ancient penguins and modern penguins similar in certain regions. However, after analyzing the endocast and comparing it to modern penguin brain anatomy, no such similarity was found, Proffitt said. The brain anatomy had more in common with skulls of modern relatives that both fly and dive such as petrels and loons, than modern penguins. “It's difficult to know why modern penguins' brains look different than their ancestors' brains”, Proffitt said. It's possible that millions of years of flightless living created gradual changes in the brain structure. But the analysis shows that these changes are not directly related to initial loss of flight because they are not shared by the ancient penguin brain. However, similarities in the brain shape between the ancient species and diving birds living today suggest that diving behavior may be associated with certain anatomical structures in the brain.

"The question now is do the old fossil penguins' brains look that way because that's the way their ancestors looked, or does it have something maybe to do with diving?" Proffitt said. "I think that's an open question right now."

Source: University of Texas at Austin