For one reason or another, we have a lot of old children’s books lying around our house. I was in the middle of reading one of these to my daughter over the weekend when she stopped me.
“Mommyo, why did they draw that dinosaur underwater?”
The dinosaur in question was a Brachiosaurus, which as any four-year-old can tell you, actually lived on land.
But for a long time after Elmer Riggs discovered the first Brachiosaurus fossils in 1900, paleontologists thought the huge sauropod must have lived underwater, walking along lake bottoms and sticking its head out of the water to breathe. An underwater life was thought to be the only way the dinosaur could support its great weight. The theory also rather neatly explained why Brachiosaurus had such a long neck and a nose perched on top of its skull. The idea persisted for decades, long enough for hundreds of images of Brachiosaurus and other sauropods walking underwater to be produced. You can see a rather nice example of one painted in 1941 by Zdenek Burian here.
So why did scientists change their minds?
In a 1951 article published in The Annals and Magazine of Natural History, K. A. Kermack stated that water pressure would make it physically impossible for any creature to breathe at the surface if its lungs are submerged more than a few feet. With its lungs some 20 feet below the surface, the Brachiosaurus would certainly have suffocated. So scientists moved the sauropod on land.
Strange as it seems to us now, the image of a Brachiosaurus living underwater and using its long neck as a kind of snorkel must have been a tough one to dispel from the public’s mind. If the illustration in our book is any indication, the notion of an underwater Brachiosaurus persisted until at least 1965.
But before you poke fun at those misguided folks of decades past, consider this — our own beloved image of the Brachiosaurus with its head held high to chomp on tasty treetop tidbits may be just as wrong.
Again, the reason is simple mechanics. Pumping blood to his (relatively) tiny little brain while keeping his head high would have required a tremendous amount of energy. Perhaps too much energy to be worth it in the grand scheme of things, which is why at least some paleontologists think that Brachiosaurus and other sauropods might have kept their necks low, sweeping them from side to side to vacuum up food from large areas of ground with much less effort.
Be sure to catch the update to this post here. Turns out the answer’s not quite as simple as I thought.