In the past, Mexico was not well explored for dinosaurs. From 1968 to 1974, William J. Morris and his colleagues worked in the El Gallo Formation of Baja, California. They collected partial skeletons of the large duckbilled dinosaurs Lambeosaurus laticaudus, which was estimated to be as long as 54 feet. Also collected from the somewhat older La Bocana Roja Formation were the fragmentary remains of Labocania anomala, a heavily built, meat-eating dinosaur. These were the only dinosaurs known from Mexico from more than scraps.
James M. Clark, Rene Hernandez, and other paleontologists worked a site of roughly Middle Jurassic age in Tamaulipas, Mexico. Middle Jurassic dinosaur-bearing rocks are rare; the Mexican site was the first one found in North America. Another Mexican site yielded the remains of Late Cretaceous dinosaurs, especially duckbills.
South America saw an explosion of dinosaur research with the work of Reig and Romer. Jose F. Bonaparte and his colleagues worked in dinosaur-bearing formations in Argentina. One find was a bizarre relative of Diplodocus. This animal evidently had a pair of tall, parallel sails along its neck and back. South American Cretaceous dinosaurs were unusual, having evolved on their own after the continent broke free of Africa in the Late Jurassic Period.
Bonaparte also discovered dinosaurs from the Middle Jurassic in Argentina, including the giant herbivores Patagosaurus and Volkheimeria and the meat-eating Piatnitzkysaurus. This predator strongly resembles the Late Jurassic Allosaurus from North America and may be its closest known ancestor.