As I've been slowly reorganizing the mass of technical papers on my computer (1,600+ and counting), I've occasionally blundered into an old paper or two that I had forgotten about. I've already used two to create a somewhat superficial post about reconstructions of phytosaurs earlier today, so I'll run with the theme of paleontological reconstruction with Oliver Hay's ideas about the lifestyle of Diplodocus.
Published in 1908, the article seems like a good textual companion to Charles R. Knight's famous restoration of "Brontosaurus" wading in a weedy swamp (see above). Recognizing that anatomy isn't for everyone, Hay writes;
To most persons the habits of living animals are more interesting than is their anatomy. The same is probably even more true with respect to the extinct animals. However, when it comes to determing the habits of extinct animals, their aquatic or terrestrial habitat, their modes of progression, their bearing on their limbs, their food and their ways of procuring it, their modes and attack and defense against their enemies, their manner of reproduction, etc., we meet with many difficulties.
The Sauropoda, and especially the species of Diplodocus, offer a fine illustration of the difficulties mentioned. Were they aquatic, terrestrial, or amphibious? Did they affect dry lands, or swamps, or rivers and lakes? Did they eat vegetable food or did they prey on other animals? Did they chew their food or did they bolt it? Did they bring forth live young or did they lay immense eggs? Did they make bold attacks on their enemies or where they timid and cowardly creatures? Did they walk only, or swim slowly, or did they employ both methods of transporting their huge bodies? If they walked, was it on all four legs or on the hinder ones only? If on all four, did they carry their bodies high above the ground, after the manner of the ox and the horse, or did they carry them more like the crocodiles, perhaps dragging their bellies on the ground?
Some of these questions may seem absurd to us know, especially after many of these questions have been resolved for a number of years, but no matter how much is published, many people (especially children) ask similar questions when they see the skeletons of dinosaurs in museums. The natural architecture is impressive of a sauropod skeleton by itself, but for more than 150 years there has been a strong tradition in paleontology of bringing extinct creatures to life and questions about paleobiology cannot be avoided.
Hay's take on the lifestyle of Diplodocus he begins with the general consensus among paleontologists at the time he wrote the article. According to the paper, Diplodocus spent a considerable amount of time in the water, "walked mostly" on all fours, they spent a small amount of time on dry land, they were primarily herbivorous, but they lacked the ability to chew their food. The aquatic habits of these dinosaurs were inferred from the deposits in which they were found, cited by Hay as being indicative of shallow, still swamps and lakes, perhaps connected to each other by river channels.
The teeth of Diplodocus appeared to be adapted to an aquatic habitat, too, the pencil-like teeth seeming awfully weak and puny for such a large animal. Soft water plants were thought to be the most suitable, and Hay asserted that W.J. Holland's idea of the diet of Diplodocus probably came closest to the truth. Holland thought the teeth of the sauropod were best suited to raking a nutritious scum from the surfaces of rocks in great quantities, although Hay said this would too-rapidly wear down the pencil-like teeth of the dinosaur. Instead, Diplodocus ate floating algae and soft, underwater plants, avoiding coarser terrestrial plants. More specifically, Hay envisioned Diplodocus lolling about in the tepid Mesozoic pools, gathering up huge amounts of algae in its mouth like a living shovel. As it gathered the algae, the teeth would be used as a slotted spoon, the tongue pressing the algae against the comb to squeeze out excess water to make room for more plant material.
Hay then moves on to criticize the posture of many restorations in print and in fossil halls. Although I have not read H.F. Osborn's treatment of Diplodocus, Hay says that Osborn envisioned the sauropod as being primarily aquatic, perhaps with a vertical fin to help it move about (although it could stand up on its hind legs as shown in a seldom-seen painting by Knight, see below). Osborn's somewhat fanciful opinion was widely criticized, but Hay also have problems with restorations showing Diplodocus in a "mammalian" posture. Instead, Hay strongly believed that Diplodocus had a sprawling posture akin to living crocodiles, a critique that Holland cut down in a scathing 1910 paper. (Thanks to Matt for setting me straight.)
A key piece of the argument in Hay's piece was the question of what Diplodocus did when resting. No one had said that Diplodocus couldn't have rested on its belly, legs out to the side, so why couldn't it have done so? To Hay, the only alternatives were the dinosaur lying down on its side like an ox or drawing its legs beneath itself like a dog or cat, both of which were too ridiculous even to be entertained. To Hay, only the crocodylian posture was suitable from anatomical and behavioral standpoints, even though he said he knew of no one other than himself who advocated such an interpretation.
Concluding his remarks, Hay saw it as a great shame that most museums had not adopted the crocodylian posture that was "truer to nature." In Hay's mind, the great sauropods passed most of their days in the water, their flexible "swan-like" necks dipping below the surface to gather algae. Occasionally they could haul themselves out onto dry land, but so much effort would be required that it would be a rare activity. Indeed, Hay could not accept a dinosaur that could swim, walk on land, and wade in shallow lakes; Diplodocus had its station in the swamp, and in the swamp it would stay.
One hundred years later, we know much more about sauropods than Hay did. The largest dinosaurs have been moved out of the swamp and are depicted as being as dynamic and active as the theropods that seem to be perpetually after them. Hay was wrong about the posture, of course, but we should not be too unkind to Hay for his mistakes. Paleontology was still a new science and dinosaurs suffered from being considered dumb reptiles, and it would seem reasonable that if they were reptiles they would act just like over sized versions of living reptiles. Although Hay's attempt to reconstruct the lifestyle of Diplodocus came up short, I can't blame him for trying.
Hay, O.P. (1908) "On the Habits and the Pose of the Sauropodous Dinosaurs, Especially of Diplodocus." The American Naturalist, Vol. 42 (502), pp. 672-681.
Holland, W.J. (1910) "A Review of Some Recent Criticisms of the Restorations of Sauropod Dinosaurs Existing in the Museums of the United States, with Special Reference to that of Diplodocus carnegiei in the Carnegie Museum." The American Naturalist, Vol. 44, pp. 259-283
Sibbick illustrated this concept, with a hilarious picture of a sprawling Diplodocus forced to pull its belly through a trench.