Update to a Past Caterpickle: “Why did they draw that dinosaur underwater?”

Illustration of a Brontosaurus (nowadays calle...
1897 illustration of a Brontosaurus (now called Apatosaurus) by Charles R. Knight.

Regular readers will remember that once upon a time, the world’s leading paleontologists firmly believed that sauropods lived underwater. It was the only possible way that such huge beasts could have supported their own weight, right?

While researching the answer to yesterday’s question: “Could sauropods swim?” I came across several articles that touched on the aquatic sauropod. And I realized that the explanation for why paleontologists moved them out of the water wasn’t quite as simple as I had believed. It’s an interesting example of how a better  understanding of anatomy and physiology can affect even settled questions in paleontology. (If there is such a thing as a settled question in paleontology.)

The first article was this 1939 article from Roland T. Bird in which he describes the first time he found sauropod tracks along the Paluxy River in Glen Rose, Texas.  At the time it was written, Bird clearly still believed that the sauropods spent most of their time in the water.

“Sixty-seven feet of lengthy neck, backbone and tail; four pillar-like legs with hips alone fifteen feet above the base; shoulders according, and a massive basket for a middle. . . . Still such a creature once floated a vast body most of the time in lakes and lagoons where favorable plant food abounded.”

And later:

With these thoughts in mind the great dinosaur moved again for me. He was out there on the shallow mudflat coming in from deeper water, progressing in the manner of a heavy quadruped, moving slowly, leisurely, without concern. Beyond were other sauropods, but he, in the foreground, was the central figure, with the sunlight glistening on his moist skin like the glint of a wet alligator crawling on a bank to dry.

Of course, most of the time isn’t all of the time, so it seems pretty clear from this that Bird was already well on his way to thinking that sauropods would have emerged from the water to walk on land on occasion. Presumably this is the argument he makes in that 1944 article “Did Brontosaurus ever walk on land?” (Still looking for a copy of that, by the way.)

From there it would be only a relatively small step to deciding that maybe if sauropods could support their weight on land some of the time, they could support their weight on land most of the time and only enter the water when say, crossing a river as part of a migration for food. An image that fits the modern idea of sauropods a bit better than the aquatic creature of old.

(In this respect, by the way, the producers of 1925’s The Lost World look like they had very good science advisers on staff indeed. Their sauropods all walk on land very well–an idea that we fully embrace today, but which would have been less obviously true at the time that movie was made.)

As we mentioned in the previous Caterpickle, the idea of aquatic sauropods was eventually abandoned when K. A. Kermack demonstrated in 1951 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.

In doing my research for yesterday’s post, however, I came across this paper from Don Henderson of the University of Calgary. In it, Henderson states that Kermack’s conclusions, while correct as far as they go, may be irrelevant.

As it turns out, between the sauropod’s hollow bones and their probable respiratory system (which would have implemented a combination of air sacs that invaded those hollow bones and filled them with air–a system similar to the one birds use today), sauropods would have been extremely buoyant in water. In other words, they would float. Kermack’s suffocation theory depends on the dinosaurs sinking to a depth that would submerge the entire body up to the head.  Henderson’s research indicates that this scenario simply wouldn’t happen.

Time to move the sauropods back to the water? Well, no.  As you may remember from yesterday, Henderson’s research also indicates that the sauropod’s unwieldy center of gravity when submerged in water would have meant that many of them would have flipped onto their sides and not been terribly good swimmers at all.

So while sauropods may have spent a great deal of their lives in or near the water, it seems unlikely that they would have gone any deeper into it than they could comfortably wade–about chest-high for your average sauropod.

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