A Brief History of Aquatic Dinosaurs (Part 1)

Painting of some aquatic Brachiosaurus by Zdenek Burian.

Well people, after my History of Feathered Dinosaur Depictions post, I have decided to write another historical essay on the study of dinosaurs. This time, I will focus on aquatic dinosaurs. The idea that some non-avian dinosaurs were aquatic (or semi-aquatic) has been proposed off and on for nearly a century and a half. Here, I have attempted to compile at least some of these ideas. Some of them will probably already be familiar to you, but I hope I can point out at least one that you haven't heard of before. Now, without further ado, let's dive in (no pun intended).

Undoubtedly the best known example of aquatic dinosaurs being proposed is the old image of sauropods and hadrosaurs. In the former case, it was once believed that sauropods were so heavy that land could not support them, so they had to remain in water. Additional lines of evidence used to support this idea were the high position of the nostrils, compared to a whale's blowhole, and their allegedly weak teeth, that could only be used to eat soft water plants. However, this idea has long been refuted. For one thing sauropod remains are often found in what were once dry paleo environments. In addition, sauropod nostrils might have actually been located near the tip of the snout after all, and it has been shown that sauropods were probably capable of eating the somewhat tougher land plants. But probably the biggest blow to the theory came when studies found that if sauropods lived their lives underwater, the immense water pressure would have collapsed their lungs, preventing them from breathing. After all, what good are nostrils on top of your head if you can't breath from them?

With regards to the alleged aquatic hadrosaurs, this seems to have started after a mummified hadrosaur was found with some skin between the fingers that was interpreted as webbing. Also, like the sauropods, the teeth were thought to have been weak and only good for eating water plants. Finally, the tail was thought to have been good for swimming to to its flat shape. This idea, too, has been thoroughly debunked. The "webbing" was just an artifact of mummification, the teeth were strong enough for tough plants, and the tail was actually very stiff. For a more detailed discussion of both of these old ideas, I recommend The Dinosaur Heresies.

A lesser known instance of aquatic dinosaurs being suggested came from Louis Dollo in which he suggested that Iguanodon was an aquatic animal. His lines of evidence were very similar to those put forward for hadrosaurs, mainly the build of the tail and observations of a "webbing" between the digits. In addition, he attempted to explain why these dinosaurs had a bipedal stance, as opposed to the quadrapedal stance of the crocodiles he was comparing them to. Unfortunately, I have been unable to encounter much more information on this hypothesis, as Dollo only devoted a brief passage in one of his papers describing this interpretation.

There is quite a bit more I want to cover, and I feel it is too long for one post, so stay tuned for Part 2!