Argentinosaurus, a sauropod dinosaur, is one of the largest dinosaurs to have walked the earth. This extinct reptile is believed to have measured more than 123 feet (37 meters) and weighed more than 100 tons (91 metric tons)! Like all other sauropods, Argentinosaurus was a plant-eating herbivore with clawed toes and a very small brain. It had a long neck and long tail and was a slow-moving, four-footed animal. Argentinosaurus inhabited present-day Argentina during the mid Cretaceous period 96 to 94 million years ago. How did paleontologists learn all that from the few bones found? They've studied the bones so far discovered, compared them to fossils of other sauropods, and used software to determine the size and shape of what's missing.