Amargasaurus was a sauropod with a length of around 10 meters and a weight of about 2.6 tons. It had a long tail and neck, a small head, and a barrel-shaped trunk supported by four legs resembling columns. Its neck was shorter than in most sauropods, measuring 2.4 meters in length. The only known skeleton comes from the sedimentary rocks of the La Amarga Formation in northern Patagonia, dating back to the early Cretaceous period around 130 to 120 million years ago.

The most remarkable features of the skeleton were the extremely tall upward projections on the neck and the anterior dorsal vertebrae that formed a double row.

All members of the Diplodocid family, to which Amargasaurus belongs, are characterized by a box-shaped muzzle and the slender teeth at the front of the mouth suitable for cropping leaves. Amargasaurus could support itself on its hind legs and tail to reach high branches.