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25 Amargasaurus
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Amargasaurus (pronounced /əˌmɑrɡəˈsɔrəs/, "La Amarga lizard") is a genus of dicraeosaurid sauropod dinosaur from the Early Cretaceous Period (130-125 mya) of what is now South America. It was small for a sauropod, reaching 10 meters (33 feet) length. It would have been a quadrupedal herbivore with a long, low skull on the end of a long neck, much like its relative Dicraeosaurus. However, this dinosaur sported two parallel rows of tall spines down its neck and back, taller than in any other known sauropod. These spines have been reconstructed supporting skin sails, but the "skin sail" hypothesis was rejected by Gregory S. Paul in 2000.[1]


ContentsEdit

[hide]*1 Discovery and species

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[edit] Discovery and speciesEdit

[1] [2]Amargasaurus restorationThe name Amargasaurus was coined in 1991 by Argentine paleontologists Leonardo Salgado and José Bonaparte,[2] 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 Barremian through early Aptian stages of the Early Cretaceous Period, or around 130 to 120 million years ago.


[edit] PaleobiologyEdit

[3] [4]An artist's depiction of Amargasaurus, with speculative "skin sail".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.

[edit] Vertebral spinesEdit

[5] [6]Angled front view of a mounted Amargasaurus skeleton cast in the Melbourne Museum.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 sacral (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.[1]

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


[edit] ClassificationEdit

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.[3][4]


[edit] ReferencesEdit