Dinosaurs were first found in South America more than 100 years ago, but only in the past 30 years have enough paleontologists been working there for us to appreciate just how many interesting kinds of South American dinosaurs there were. Paleontologists have discovered South American dinosaurs that date from the middle of the Triassic Period to the end of the Cretaceous Period.
In particular, paleontologists are now putting together a picture of South American dinosaurs from the Early Cretaceous epoch, a stretch of time of which we know little about dinosaurs worldwide. Most of the newly discovered South American Early Cretaceous dinosaurs are various kinds of sauropods, but there are also some new kinds of theropods. Some seem closely related to certain Early Cretaceous dinosaurs from Africa, which is not surprising, because at that time South America and Africa were partly connected. Dinosaurs could have walked from one continent to the other.
Andesaurus was a normal-size sauropod about 50 to 60 feet long. Its gigantic relative Argentinosaurus just may be the world's largest known dinosaur. It was about twice the size of Andesaurus, with vertebrae about five feet tall. Both it and Andesaurus, which were both found in Patagonia, are close relatives of the titanosaurids of Late Cretaceous South America.
Another group of sauropods, called Dicraeosauridae, includes the odd-looking Amargasaurus, a tall-spined relative of the African Late Jurassic sauropod Dicraeosaurus. These were rather small sauropods (about 40 feet long) related to the giant North American Apatosaurus and Diplodocus. The vertebral spines of Amargasaurus grew especially tall along the back of the neck, where they may have been covered with webs of skin.
Another South American sauropod, Rayososaurus, is a close relative of the African Rebbachisaurus. Both dinosaurs had tall vertebral spines, but whereas the spines in Amargasaurus were paired, single spines were present in the rebbachisaurids. They may have given the animals a tall ridge along the back. The spines of Rayososaurus were not quite as tall as those of Rebbachisaurus. Both dinosaurs were standard-size sauropods, measuring about 50 to 60 feet long.
A possible relative of the rebbachisaurids is the very strange sauropod Agustinia, which had a double row of plates and spines resembling those of Stegosaurus along its back. They may have been movable. No dinosaur like Agustinia has been found anywhere else in the world.
From about the same time and place as the gigantic Argentinosaurus comes the correspondingly huge theropod Giganotosaurus. Bigger than Tyrannosaurus, it is presently the largest known meat-eating dinosaur, as much as 50 feet long. In a lagoonal deposit in Brazil was found the man-size, fish-eating theropod Irritator. It was probably related to the much bigger African spinosaur Suchomimus.