One of the greatest tasks for marine reptile paleontologists since 1868 has been deducing the use of a neck like the lengthy one we find attached to the body of Elasmosaurus. Just like with sauropods, the neck of Elasmosaurus has been discussed, debated, and drawn many different ways over the past 145 years. The mystery has slowly unraveled over that time, but today we shall briefly look at the history of the interesting apparatus that is the long necked plesiosaur's neck (short necked plesiousars, examples of these are found in the polycotylid and pliosaur families, are visibly different from the long necked plesiosaurs).
Cope's original illustrations of Laelaps, Elasmosaurus, and Hadrosaurus appear nearly comical these days. The Mosasaur in the background we will leave for another day, however, the Elasmosaurus gives us plenty to talk about right now. Cope's Elasmosaurus, in his illustration, possesses the original configuration which Cope published erroneously. The exceedingly long tail is stupendous and, prior to looking at other illustrations, it is fairly easy to understand why Cope would assume that so long a column of vertebrae would be found in a tail rather than a neck. The eyes were fairly accurately portrayed in terms of position, but even the small neck would not have been as flexible as Cope portrayed it to be. The strangely small forelimbs and the fact that it is floating on the top of the ocean water are equally erroneous. That turtle right behind Elasmosaurus sure looks happy though.
Charles R. Knight 1897
Move forward nearly 30 years to Charles R. Knight, one of the most prolific wildlife (though prehistoric) painters in American history. Knight, using the readjusted skeleton of Elasmosaurus, painted this wonderful plate for a magazine published in black and white in 1897. The body, overall, is accurate even today, with the exception, once again, of that grossly exaggerated neck flexibility. It has, fairly recently, been proven and shown through models (fossil bones are usually far too fragile to actually string and grind together) that the neck of a plesiosaur, especially this very long neck of Elasmosaurus, was not able to perform the snake-like strikes that are often depicted in older illustrations such as this one. The vertical position of the body of the second Elasmosaurus is also quite odd, though of course it would be able to swim vertically at times. The strike posture it seems to be taking in this image, though, is rather bird-like or snake-like and would probably have been difficult to maintain for any length of time (not to mention the inability of the animal to strike like a snake as previously mentioned).
Find me an artist, win a cookie!
Enter the modern era. Elasmosaurus and other plesiosaurs have been updated from the dolphin like ballerina-swimmers making quick snake like strikes to graceful, yet slower, swimmers which possessed long but horizontally inflexible necks; vertical flexibility was a bit larger in range, though not as much as Knight and Cope depicted. Now Elasmosaurus is thought to have catch small fish and, by some, crunch down on some small shelled animals. Its slow but graceful swimming habits have been described many ways, as there are many models of the swimming mechanism which may have been present in these large plesiosaurs. Often, though, it is depicted as a rowing motion, a penguin-like flapping, or even a hummingbird-like figure eight motion. Regardless of which version of locomotion is favorable, catching fish like a plesiosaur would have involved a bit of stealth in striking from below, using the long neck as a way to get the head close without the body being seen by the prey. A concerted effort of many plesiosaurs circling and balling up prey to invoke a "feeding ball" (if anyone else has used the term I do not know of it so I am claiming it as my own for now) is another alternative means of feeding. This would involve a gathering of fish forced into a large living and writhing mass by circling predators which the plesiosaurs could then dart into, at their slow speed even, and grab fish.