It was a moderately large (?15 m long) cetiosaur-like sauropod found in the Middle Jurassic (?Callovian) Cañadon Asfalto Formation at Fernandez Estancia, Chubut Province, Patagonia, Argentina; known from a 50% complete skeleton (Holotype: MPEF-PV 1125 (Museo Paleontologico Egidio Fergulio)), lacking a skull, but including dorsal, sacral and caudal vertebrae, parts of the forelimbs and hindlimbs, parts of the shoulder girdle and pelvis, some rib fragments, and skin impressions.
Tehuelchesaurus is most similar to Omeisaurus from the Middle Jurassic of China, but is distinguished by the shape of the coracoid, the stouter radius and ulna, and the shapes of the pubis and ischium; all the dorsal vertebrae have pseudopleurocoels (deep depressions in the centra but without internal chambers) and opisthocoelous centra, unlike in Barapasaurus and Patagosaurus. The length of the entire neck and tail are not known, but based on other proportions (humerus 1.14 m long; femur 1.53 m long; scapula 1.75 m long; ischium 1.01 m long; ilium 1.12 m; pubis .943 m long), Tehuelchesaurus was probably about 15 m (50 ft) long. It was discovered by Rich, Vickers-Rich, Gimenez, Cuneo, Puerta & Vacca in 1999.
Type species: Tehuelchesaurus benitezii [bay-nee-TAY-see-ie] Rich, Vickers-Rich, Gimenez, Cuneo, Puerta & Vacca: for Aldo Benitez, who discovered the holotype.