Although this animal's remains were first mentioned in print in 1959, it was not named until the description written by Brazilian paleontologists Rodrigo Santucci and Reinaldo Bertini in 2006. It was the first dinosaur named in that year. The only species (A. mezzalirai) is named in honor of Sergio Mezzalira, the Brazilian geologist who originally found the specimen and first mentioned it in print. The genus Adamantisaurus is named after the Adamantina Formation in the Brazilian state of São Paulo, where the fossil was found and also incorporates the Greek word sauros meaning 'lizard', the most common suffix used in dinosaur names.
The Adamantina Formation is part of the Bauru Group of geologic formations. The stratigraphy and exact age of the Bauru Group is still unsettled, but the Adamantina probably occurs somewhere between the Turonian through early Maastrichtian stages of the Late Cretaceous Period (93 to 70 million years ago). Adamantisaurus shares the Adamantina with fellow titanosaurian, Gondwanatitan.
Like many titanosaurians, Adamantisaurus is incompletely known, making its exact relationships difficult to establish. However, similarities have been noted with Aeolosaurus and the Bauru Group titanosaurian formerly known as the "Peiropolis titanosaur", now called Trigonosaurus (Santucci & Bertini, 2006).