Pisanosaurus

Pisanosaurus ("PIE-san-uh-SAWR-us") is a genus of primitive ornithischian dinosaur from the Late 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. The fossils were discovered in Argentina's Late Triassic Ischigualasto Formation, which dates to about 228 to 216.5 million years ago.

The exact classification of Pisanosaurus has been the topic of debate by scientists for over 40 years; the current consensus is that Pisanosaurus is the oldest known ornithischian, part of a diverse group of dinosaurs which lived during nearly the entire span of the Mesozoic Era.