Penguins used to be very different tens of millions of years ago – for one thing, they could fly. Eventually, they transitioned to becoming expert divers and adapted to foraging food from the depths of the ocean. It’s a logical assumption to make that this drastic change in lifestyle would have also led to a marked change in brain structure, but a new study in the Journal of Anatomy finds that this wasn’t the case.

The environment an animal evolves in is known to be able to strongly influence the structural development of its brain. For instance, the brains of birds in the Corvidae family, which include crows and ravens, have a “puzzle-solving” region that allows them to craft basic woodland tools and form complex social heirachies. And in octopuses, their brains are somewhat "spread” throughout their eight tentacles, making them partly autonomous; this allows them to navigate the sea and ambush prey with remarkable precision and ease. 

To find out if the same is true for penguins, a team of researchers decided to look back through their evolutionary history. The point at which penguins became grounded and gave up on roaming the skies should, in theory, have caused their brain structure to change.

Although the brains of ancient penguins have long since disintegrated, their fossilized skulls would provide the researchers with the next best thing: A “cast” of the missing brain. Tracking changes in skull shape over time would allow the researchers to see when new, significant underlying brain structures may have developed.

The fossilized skull of the Waimanu ancestral penguin, one that lived in New Zealand around 60 million years ago, was chosen. “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,” James Proffitt, lead author of the study and a graduate at the University of Texas at Austin, said in a statement.

^{The ancient penguin’s skull (A) and a digital model of it (B), with various neurological features labelled including the cerebellum, ce. Scale bar is 2.5 centimeters. James Proffitt.}

X-ray scans were used to digitally capture the skull’s shape, which was then used to create a 3D digital model of the brain. Comparing it to the skull anatomy of various living penguins, the researchers were hoping to see two fairly similar brains, since neither the ancestor nor modern penguins could fly.

Curiously, the brains were notably different. In fact, they found that its brain is more similar to modern-day birds that both fly and dive to some extent, such as the petrel, which makes sense considering the Waimanu is from the transition period between flight and diving.

This shows that the loss of flight did not cause a relatively sudden, dramatic change in the brain structure of penguins. It appears to be more likely that millions of years living as flightless birds caused gradual changes in their brain structure.

Although it would certainly be useful for penguins to still be able to fly and escape sticky situations, their investment in becoming expert divers means that this ability has been lost. This is another example of how evolution works: A species can either become the jack-of-all-trades type, or the master of just a handful of skills.