In Star Wars: Episode IV - A New Hope, C-3PO passes by what looks like a dinosaur skeleton:
What is this creature? Are they extinct? How did such a large animal manage to survive in a barren desert?
It is from a Greater Krayt dragon: http://starwars.wikia.com/wiki/Krayt_dragon
The krayt dragon was a large carnivorous reptile native to Tatooine.
They are extinct, Obi-Wan imitated the hunting cry of a Krayt dragon to scare away the sand people.
The greater krayt was a rarer, larger species of krayt dragon, known for its tremendous size and continual growth over time. Creatures of near legendary status, greater krayt dragons had ten legs, measured at least 100 meters from snout to tail tip and had the ability to move through or on Tatooine's desert sand
The artificial skeleton used for A New Hope was left in the Tunisian desert after filming and still lies there. During filming of Attack of the Clones, the site was visited by the crew and the skeleton was still found there.