Saltasaurus

  
      Saltasaurus was a small sauropod of the late Cretaceous, characterized by a diplodocid-type head (with blunt teeth only in the back of the mouth) and was the first exposed with small bony plates entrenched in its skin. The bony plates (osteoderms) have since been found in other titanosaurids, and a crest of scutes has also been discovered running down the back of diplodocids. When the plates of a saltosaur were at first found independently of skeletal remains, they were unspecified to be from an ankylosaurian, whose plates they resemble.
Changing perceptions

      In the Cretaceous period, sauropod dinosaurs in North America were behind the survival game to duck-billed dinosaurs, such as Edmontosaurus. However, like modern Australia, South America was an island continent and life evolved rather in a different way there. Specifically, the duck-billed dinosaurs never gained a foothold and so sauropods, purposely the titanosaurids, sustained on their own path of evolution.

     Saltasaurus (which means "lizard from Salta") was one such highly-evolved sauropod, and lived 70 to 65 million years past. When it was first discovered in 1980, it enforced palaeontologists to reconsider many of their assumptions about what was and what was not a sauropod because Saltasaurus, though clearly a sauropod, had armour plating. Previously, it had been assumed that size alone was sufficient defense for the massive sauropods.

     However, a Saltasaurus was exposed with covered with bony knobs 10 to 12 centimeters (4 to 5 inches) in diameter. Since then, palaeontologists have investigated the option that other sauropods also had armour; for example, the Argentinian Laplatasaurus.