Amargasaurus

*Amargasaurus cazaui*

* Jurassic Park Institute Artwork
* Robert F Walters Artwork

***Amargasaurus*** was a relatively small (10 meters) sauropod that lived in the early Cretaceous period. It was unique because it had two rows of spines - once believed by some paleontologists to have supported a sail - running down its neck. Amargasaurus is known from an almost complete skeleton (it is missing the front of the skull and the tail). Amargasaurus was found in La Amarga, a canyon in Argentina.

## Description

*Amargasaurus* was a sauropod from the early Cretaceous period. This plant-eater was about 33 feet (10 m) long and weighed roughly 5000 kg. It had two rows of spines growing out along its backbone along its neck, body, and tail. These spines may have had one or two coverings of skin forming a sail.

## History

The name *Amargasaurus* was coined in 1991 by Argentine paleontologists Leonardo Salgado and José Bonaparte, because its fossil remains were found alongside the La Amarga Arroyo in the Neuquén province of Argentina. La Amarga is also the name of a nearby town, as well as the geologic formation the remains were recovered from. The word *amarga* itself is Spanish for "bitter," while *sauros* is Greek for "lizard." The one named species (*A. cazaui*) is named in honor of the man who discovered the site, Dr. Luis Cazau, a geologist with the YPF oil company, which at the time was state-owned.

This site is located in the lower (older) sections of the La Amarga Formation, which dates to the Early Cretaceous Period, or around 130 to 120 million years ago.

## Classification

*Amargasaurus* and *Dicraeosaurus* are united with the more recently discovered *Brachytrachelopan* in the family Dicraeosauridae. Dicraeosaurids and diplodocid sauropods are included in a group called Flagellicaudata.

## Paleobiology

Amargasaurus is known from a relatively complete skeleton from a single individual. This skeleton includes the back of the skull, and all vertebrae of the neck, back, and hips, as well as a bit of the tail. The right side of the shoulder girdle is also known, as are the left forelimb and hind limb, and the left ilium, a bone of the pelvis.

### Vertebral spines

The most obvious feature of *Amargasaurus'* skeleton is the series of tall spines on the neck and back vertebrae. The spines are tallest on the neck, where they are paired in two parallel rows. These rows continue along the back, decreasing in height as they approach the hips. The lower back and hip vertebrae feature only single spines, which are long but much shorter than those of the neck, comparable to other sauropods. These spines may have supported a pair of tall skin sails. Similar sails are seen in the unrelated dinosaurs *Spinosaurus* and *Ouranosaurus*, as well as the pelycosaurs *Dimetrodon* and *Edaphosaurus*. There are a variety of hypotheses for the function of these such sails, including defense, communication (for mating purposes or for simple species recognition), or temperature regulation.

Gregory Paul argued that parallel neck sails would have reduced neck flexion. Instead, he proposed that, with their circular rather than flat cross-sections, these spines were more likely covered with a horny sheath. He even suggests that they could have been clattered together for a sound display.

Similar spines are found on the presacral vertebrae of *Dicraeosaurus* from Africa, although not nearly as tall.

## JPInstitute.com Description

A medium-sized member of the sauropod family, Amargasaurus had a short neck with a double row of tall spines on top. The purpose of these spines is not clear, but they may have supported a fleshy sail, or may have been covered in a hard, horn-like sheath.

The splitting of the neural spines is common in the diplodocoidea, but reached a most extreme form in the Amargasaurus, developing into spines 50 cm (1.5 Feet) long. Amargasaurus had peg-like teeth, and could not chew its food, so it swallowed "gizzard stones" that aided in the digestive process.

Amargasaurus is known from a single set of fossils, found without a tail, so its size is not certain.

## Dinosaur Field Guide Description

Amargasaurus ("lizard from La Amarga (geologic formation]) is one of the most unusual sauropods known to science. Its most distinguishing feature is the tall double row of spines, like two sails, coming out of the back of its neck. These sails served many functions--at a price. They made the dinosaur look much bigger than it was, possibly keeping predators away. The sails could also be used under certain conditions--like a solar panel, gathering heat when facing into the sun and losing heat when in the shade. Unfortunately, the sails were also very restrictive and would severely limit the range of motion in Amargasaurus's head and neck. They were also very fragile and would get seriously damaged if bitten.

### Fun Facts

Some Amargasaurus neck spines are 19.6 inches (50 cm) long

### Trivia

The only mounted skeleton in the world is in Buenos Aires, Argentina,

## Links

http://web.archive.org/web/20031006065532fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_amarg.html

## References

Template:References

1. ↑ Salgado L & Bonaparte JF. (1991). Un nuevo sauropodo Dicraeosauridae, *Amargasaurus cazaui* gen. et sp. nov., de la Provincia del Neuquén, Argentina. *Ameghiniana* 28: 333-346. [in Spanish]
2. ↑ Rauhut OWM, Remes K, Fechner R, Cladera G, & Puerta P. (2005). Discovery of a short-necked sauropod dinosaur from the Late Jurassic period of Patagonia. *Nature*. 435: 670-672.
3. ↑ Taylor MP & Naish D. 2005. The phylogenetic taxonomy of Diplodocoidea (Dinosauria: Sauropoda). *PaleoBios*. 25(2): 1-7.
4. ↑ Paul, Gregory S. (2000) *The Scientific American Book of Dinosaurs*, p 94. St. Martin's Press. ISBN 0-312-26226-4.