When penguins went from winging across the sky to swimming and toddling on ice and soil, their brain structure didn't alter as a result of the switch away from flying.
Researchers from the University of Texas at Austin (UT) made this finding after analyzing the oldest-known penguin fossil's skull.
"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," James Proffitt, study leader, at UT said. "The way the modern penguin brain looks doesn't show up until millions and millions of years later."
The skull is at the Canterbury Museum in Christchurch, New Zealand. The penguin itself lived in that country more than 60 million years ago, in the Paleocene epoch. Just as an aside, at the beginning of that epoch, Earth was recovering from a recent asteroid impact and was subtropical almost from pole to pole.
The penguin that lived way back then was likely not living very differently from the average penguin today. But diving in water was relatively new for that ancient toddler.
"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.
In the study, Proffitt employed X-ray CT-scanning, capturing digital detail of the anatomy of the skull. The team then made a digital "mold" of the brain using computer modeling software. The mold is known as an endocast.
That endocast showed that the ancient penguin had more in common with some relatives in the present day that fly and dive as well, including loons and petrels. Loons dive underwater in search of prey and propel themselves with their feet; they consume prey underwater. Petrels can sometimes resemble miniature penguins on the sea surface, and they dive as well.
That said, if diving birds of today and ancient species of new divers (the ancient penguin) have similarities in brain shape, this implies that diving behavior may be related to certain structures of brain anatomy.
The findings were published in the Journal of Anatomy in February.