Amargasaurus

Amargasaurus is a genus of sauropod dinosaur from the Early Cretaceous epoch of what is now Argentina. The only known skeleton was discovered in 1984 and described in 1991, forming the holotype specimen of the single species Amargasaurus cazaui. The skeleton is nearly complete, including a fragmentary skull, making Amargasaurus one of the best-known sauropods from the Early Cretaceous. Amargasaurus was small for a sauropod, reaching 9 to 10 meters in length. It sported two parallel rows of tall spines down its neck and back, taller than in any other known sauropod. It is unclear how these spines appeared in life—they could have supported skin sails or stuck out of the body as solitary structures supporting a keratinous sheath. They might have been used for display, combat, or defense.

Amargasaurus was discovered in sedimentary rocks of the La Amarga Formation, which dates back to the Barremian and late Aptian of the Early Cretaceous epoch. It shared its environment with at least three other sauropod genera, which might have exploited different food sources in order to reduce competition. Amargasaurus probably fed at mid-height, as shown by the orientation of its inner ear and the articulation of its neck vertebrae, which suggest a habitual position of the snout some 80 centimeters above the ground and a maximum height of 2.7 meters. Within the Sauropoda, Amargasaurus is closely related to the Late Jurassic genera Dicraeosaurus, Brachytrachelopan and Suuwassea. Together, these genera form the family Dicraeosauridae, which differ from other sauropods in showing very short necks and small body sizes.