Patagosaurus (meaning "Patagonia reptile") is an extinct genus of eusauropodan dinosaur from the Middle Jurassic of Patagonia, Argentina. It was first found in deposits of the Cañadon Asfalto Formation, which date from around 165 to 161 million years ago. Although originally twelve specimens were assigned to the taxon, at least one of them may belong to a different genus. Patagosaurus probably lived alongside genera such as Piatnitzkysaurus, Condorraptor, Volkheimeria and another unnamed sauropod.
Since Patagosaurus is known from many specimens, including at least one juvenile, its anatomy and growth are fairly well understood. Both ages exhibit the typical features of a sauropod, a long neck, small head, a long tail, and being quadrupedal. The juvenile exhibits features different from the adult in regions like the mandible, pectoral girdle, pelvis and hindlimb, although overall their anatomy is quite similar. The many known specimens help fill in gaps in the anatomy of the genus, such as the forelimb and skull. Parts of the skeleton, like the pectoral girdle, tibia and pubis, are more robust, while others, like the forelimb and ischium, are more gracile. The material of Patagosaurus is similar to closely related taxa like Cetiosaurus and Volkheimeria, more primitive genera such as Barapasaurus and Amygdalodon, and more derived sauropods like Diplodocus and Camarasaurus.