The only known specimen of Rayososaurus agrioensis was discovered in 1991 by a team led by José F. Bonaparte, at a locality three kilometers south of Agrio del Medio in Picunches Department, Neuquén Province, Argentina.

Bonaparte believed that the strata the specimen was excavated from belonged to the Rayoso Formation, and named the genus after it.

[2] Efforts undertaken in 2008 and 2009 re-located the original locality and determined that the specimen actually came from the upper layers of the Candeleros Formation.

[3] In 1998, Jeffrey Wilson and Paul Sereno proposed assigning Rebbachisaurus tessonei to Rayososaurus.

[3] The Candeleros Formation, where the specimen was found, dates to the Cenomanian age of the Late Cretaceous.