Raphus cucullatus disappeared forever in 1662, less than 30 years after humans first set up permanent camp on their native island of Mauritius. Not long before then, sailors who visited the island started hunting the birds for food. Because humans were able to usher the birds onboard and keep them docile and overfed until slaughtering time, our lasting impression of the dodo is of a lumbering, fatally stupid flightless beast. In reality, they were easy to herd onto ships because they'd never encountered humans and didn't know enough to fear us – and they looked comically plump because hungry sailors fattened them up.
"I was not on a mission to redeem the dodo, but that's what it turned out to be," said lead author Eugenia Gold, a research associate and recent graduate of the American Museum of Natural History's Richard Gilder Graduate School and an instructor in the Department of Anatomical Sciences at Stony Brook University.
Gold first CT-scanned a dodo specimen – a rare find, even in natural history museum collections – as part of a larger project for her dissertation. She quickly noticed that the size of the long-dead creature's brain case suggested a brain about the same size (relative to body mass) one would see in modern pigeons. The dodo is technically a kind of pigeon, but it's not usually associated with its sleek, flying cousins.
In addition to the overall size of the brain case, Gold noted that the dodo she studied had a mysterious quirk never seen in another bird: an unusual curvature of the dodo's semicircular canal -- the balance organs located in the ear.
"We don't see this strangeness repeated in any other bird, so for now we are uncertain as to the meaning," Gold told The Washington Post.
It also shared unusually large olfactory bulbs with Rodrigues solitaire, the bird species closest to it on the family tree – and one that was also recently driven to extinction by humans. Birds usually rely more on sharp-sightedness than on a keen sense of smell, Gold explained, but the dodo and the solitaire probably inherited these oversized olfactory centers from their last common ancestor to help the flightless birds sniff out food on the ground.
A bigger overall brain doesn't necessarily mean a smarter animal – even if we're talking about brain size relative to body size. But some scientists do believe that comparing the relative brain sizes of closely related animals can show a correlation between their intelligence relative to one another.
"There is a lot more to intelligence than just brain size, and I do have that caveat in the paper," Gold said. "We used brain volume or size as a proxy for intelligence, and since the dodo brain is proportional to its body size, then we can hypothesize that it may not have been as dumb as we thought, or at least as intelligent as other pigeons. Unfortunately, measuring intelligence in an extinct animal is quite tricky, and using brain volume might be the one of the only proxies we have for it."
If Gold can find more brain cases, she said, she'll at least be able to take steps to confirm that the brain size and shape of the dodo she studied was normal. For now, her work provides an intriguing glimpse at an unfairly maligned bird.