Puertasaurus is a genus of sauropod dinosaur that lived in South America during the Late Cretaceous Period. It is known from a single specimen recovered from sedimentary rocks of the Cerro Fortaleza Formation in southwestern Patagonia, Argentina, which probably is Campanian or Maastrichtian in age. The only species is Puertasaurus reuili. Described by the paleontologist Fernando Novas and colleagues in 2005, it was named in honor of Pablo Puerta and Santiago Reuil, who discovered and prepared the specimen. It consists of four well-preserved vertebrae, including one cervical, one dorsal, and two caudal vertebrae. Puertasaurus is a member of Titanosauria, the dominant group of sauropods during the Cretaceous.
Puertasaurus was a very large animal. Its size is difficult to estimate due to the scarcity of its remains, but current estimates place it around long and in mass. The largest of the four preserved bones is the dorsal vertebra, which at wide is the broadest known vertebra of any sauropod. The Cerro Fortaleza Formation is of uncertain age, due to the inconsistency of stratigraphic nomenclature in Patagonia. When Puertasaurus was alive, the Cerro Fortaleza Formation would have been a humid, forested landscape. Puertasaurus would have shared its habitat with other dinosaurs, including another large sauropod, Dreadnoughtus, in addition to other reptiles and fish.
The holotype and only known specimen of Puertasaurus reuili was discovered in the Santa Cruz Province of southern Patagonia, Argentina. The remains were recovered in Cerro Los Hornos, near the La Leona River, and were reported from the Cerro Fortaleza Formation (which, at the time, was referred to as the Pari Aike Formation). The holotype was discovered in a grey sandstone lens that also preserved the carbonized remains of cycads and conifers. It was given the specimen number of MPM 10002, and consists of four vertebrae, specifically one cervical, one dorsal, and two (about 3% of the skeleton). Of this material, only the dorsal vertebra was complete.