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| ©Casliber, taken from Wikipedia |
Amargasaurus, as stated yesterday, has a very intriguing array of vertebral neural spines arching above its neck and body. Here we have the naked spines, a cast thereof anyhow, which shows exactly how outrageous the neural spines are. There is nothing like an interesting adaptation which is as mysterious as it is jaw droppingly intriguing in a dinosaur. Regarding animals like the Ceratopsians we can make some fairly valid assumptions regarding defensive and communication, either of identification, mating purposes, or simply to identify members of a herd, intents of their frills and horns, with Amargasaurus, however, the intent of the neural spines is highly debated. There is certainly an element of display inherent in the spines regardless of the type of covering they bore in life, as we shall look at momentarily.
The first, and it seems most obvious adaptation noted by paleontologists, was that of a tightened skin membrane stretched between the neural spines to form a sail along the length of the body as far as spines stretched out of the back of Amargasaurus' body. There are many practical uses for a sail beyond the one trait, display and communication, we will consider valid with any of the three body types associated with the spines. One of these, of course, is thermoregulation. Regardless of how one feels about dinosaurs being warm-blooded, and there certainly are those that still feel that they are not, which is fine, the ability to help an animal as large as Amargasaurus to either cool down in summer or warm itself in winter simply by flushing more blood into the sail to be warmed or cooled is a theory that could definitely hold some ground. This, additionally, is a way that the dinosaur could have used the sail for communication as well; flushing eyespots in the sail at predators or appearing healthier during mating season by being more vibrant.
The Luis Rey illustration and this slightly older illustration from Nobu Tamura, always a friend to us here and always very willing to allow us to view his art, both champion the theory of Amargasaurus as it is. The spines themselves would not have been an active weapon; most likely the whip-like Diplodocid tail would have been used in that regard long before the dinosaur tried to use the neural spines in an offensive manner. Though it can be noted that spikes of bone covered in a keratin (think fingernails and rhino horns) sheath would have made a very formidable passive defense for the neck and upper torso of Amargasaurus. The length of the spines, in terms of display, would have been, basing this observation on extant animals' determinations of male prowess, the major factor in courtship displays and mating confrontations that ended without violence. Additionally, the spines may have had strong muscle attachment sites which allowed them to be flexed, like a cat's hackles for instance, in aggression displays towards rivals or predators.
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| Courtesy National Museum of History, London |
The final proposed idea for those neural spines has been a camel-like hump down the length of the back in which the spines support the fatty tissues that make up the hump and give it some stability. This theory is not illustrated out as much as the other two theories, in part because it does not have the support that the other two theories entertain these days. The hump does have a logical use of course or it never would have been proposed to begin with and one explanation for the need for it would be an extended dry season in the environment in which Amargasaurus lived. In terms of ability to display with a hump like this, there is a little less ability to flash signals and to move the hump as there are in the spine or sail modifications that were previously discussed. The hump, therefore, would more than likely be mostly functional in terms of survival than communication.
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