Andesaurus ( ; "Andes lizard") is a genus of basal titanosaurian sauropod dinosaur which existed during the middle of the Cretaceous Period in South America. Like most sauropods, belonging to one of the largest animals ever to walk the Earth, it would have had a small head on the end of a long neck and an equally long tail. History of discovery In 1991, paleontologists Jorge Orlando Calvo and José Fernando Bonaparte named Andesaurus, which refers to the Andes and also includes the Greek word sauros ("lizard"), because of the proximity of this animal's remains to the Andes. Andesaurus fossils were found by Alejandro Delgado, after whom the single known species (A. delgadoi) is named. The only known material of Andesaurus is a partial skeleton consisting of a series of four vertebrae from the lower back, as well as 27 tail vertebrae, divided up into two series from separate parts of the tail. The vertebrae from the middle part of its tail had elongated centra. Elements of the pelvis were also discovered, including two ischia and a pubis bone, along with rib fragments and an incomplete humerus and femur. Description Andesaurus was a medium sized sauropod, reaching in length and in body mass. The dorsal vertebrae of Andesaurus bear the typical features of an centrum and large lateral (pneumatic depression). Unlike related Phuwiangosaurus, there is no ventral keel under any of the vertebrae, and there is a pneumatic feature on the front of the , the latter being found in most neosauropods. Potentially diagnostic for Andesaurus, there is an additional ridge supporting the lower articulation for the ribs (), although poor preservation in other vertebrae means it can only be identified on one bone. The of Andesaurus are smaller than more basal sauropods, but less reduced than in Argentinosaurus or Epachthosaurus, where the surface is only articular ridges, and also less reduced than more derived titanosaurs where the articulation is entirely absent. Pre- and post-spinal are present in the vertebrae of Andesaurus, like in other somphospondylans. Tail vertebrae (caudals) of Andesaurus are slightly , where the anterior face is concave and the posterior face of convex. This convexity is less prominent than more derived titanosaurs, but is still diagnostic of the clade as a whole. The first caudal has a flat anterior and slightly convex posterior face, different from the subsequent vertebrae similar to in Epachthosaurus. A prominent depression is