Named By: Leonardo Salgado & José Bonaparte - 1991.
Classification: Chordata, Reptilia, Dinosauria, Saurischia, Sauropodomorpha, Sauropoda, Diplodocoidea, Dicraeosauridae.
Species: A. cazaui (type).
Size: 10 meters long.
Known locations: Argentina, Neuquén province - La Amarga Formation.
Time period: Barremian to Aptian of the Cretaceous.
Fossil representation: Quite well preserved individual that includes a partial skull, left fore and aft limb, left ilium, right shoulder, all cervical (neck), dorsal (back), sacral (sacrum) and some caudal (tail) vertebrae.
as famous as some sauropods
appearance of Amargasaurus has made it a firm
favourite amongst many
who are interested in dinosaurs. Two rows of spikes, the largest of
which are on the neck run all the way down the back of Amargasaurus
from the head to the end of the tail. There are two main theories to
what these spines looked like in life, the first one being that they
were supports for a double sail. The second is that there was no skin
sail at all, and that the spikes would have been covered by horn.
This is based upon the idea that a skin sail would have made the
neck too rigid to bend, although this would be more down to how much
the neck had to bend in order for Amargasaurus to
drink and feed.
Aside from what a living Amargasaurus looked like, another question would be why it had these enlarged spikes. Predator defence is a possibility but it seems unlikely as if this were the case you would expect the spines to have been enlarged and equally sized over at least the whole back of the body as well. If a sail was carried by the spines then thermoregulation is something to consider, however this is also unlikely as no other sauropod is known to have needed such a temperature regulation device. Also two sails close together would have shielded one another from the wind making them at best half as efficient as a single sail.
The most likely reason for the spines is that of species recognition and possibly display. Large spikes may have meant that an Amargasaurus was mature and ready to mate. The spines may have only been on the neck so that when a male Amargasaurus mounted a female he would not impale himself upon the female’s spines. Another theory suggests that the spines may have been rattled together in a form of auditory display by Amargasaurus shaking its neck from side to side. Again older individuals may have had larger spines that created more noise, signalling their seniority to younger individuals. Finally and briefly returning to the skin sail theory, a sail would have allowed Amargasaurus to more easily recognise others of its kind over long distance. A sail may have also become more brightly coloured during the breeding season signalling an individual’s level of fitness and readiness to mate.
The overall body shape of Amargasaurus has seen it classed as a diplodocid sauropod (same group as Diplodocus), and Amargasaurus is thought to have been most closely related Dicraeosaurus from Tanzania which also had spines along its back. Another interesting sauropod from the Cretaceous of South America is Agustinia.
- Un nuevo saurópodo Dicraeosauridae, Amargasaurus cazaui gen. et sp. nov., de la Formación La Amarga, Neocomiano de la provincia del Neuquén, Argentina [Amargasaurus cazaui gen. et sp. nov., a new dicraeosaurid sauropod from the La Amarga Formation, Neocomian of Neuquén province, Argentina] - Ameghiniana 28(3-4):333-346 - L. Salgado & J. F. Bonaparte - 1991.
- Cranial osteology of Amargasaurus cazaui Salgado and Bonaparte (Sauropoda, Dicraeosauridae) from the Neocomian of Patagonia - Ameghiniana 29: 337-346. - L. Salgado & J. O. Calvo - 1992.
- Giants and bizarres: body size of some southern South American Cretaceous dinosaurs - Historical Biology 16 (2-4): 71–83. - G. V. Mazzetta, P. Christiansen & R. A. Farina - 2004.
- The sauropod diversity of the La Amarga Formation (Barremian), Neuquén (Argentina) - Gondwana Research 12:533-546 - S. Apesteguia - 2007.