It is known from five fossilized and assorted teeth, but is diagnosed by a unique combination of characters.

[1][2] Clasmodosaurus was named by Florentino Ameghino in 1898, but remained largely unknown for decades after its discovery.

[2] Like Loncosaurus, its taxonomy remained unclear with it regarded as a theropod on the rare occasions it was mentioned.

[2] However, Jaime Powell suggested that it was a dubious genus of sauropod in 1986, an identification which has been accepted since.

[1] The teeth of Clasmodosaurus spatula were polygonal in cross section rather than round, an unusual trait also found in the titanosaur Bonitasaura salgadoi.