Pisanosaurus

Pisanosaurus (meaning "Pisano lizard") is a genus of primitive ornithischian dinosaur from the Upper Triassic of what is now South America. It was a bipedal herbivore described by Argentine paleontologist Rodolfo Casamiquela in 1967. Only one species the type, "Pisanosaurus mertii", is known, based on a single partial skeleton. 
It is the oldest known ornithischian.