The Lessemsaurus was described by Jose Boneparte in 1999. This dinosaur is a sauropodomorph. It was named after a famous writer named Don Lessem. These were long-necked herbivores that walked on four legs.

Fossils of the Lessemsaurus were found in Los Colorados Formation in La Rioja province, Argentina. This area was very popular for discoveries of several Late Triassic Dinosaur fossils such as Coloradisaurus, Coloradia, Zupeysaurus, RioJasauris, and Strenusaurus.