Its fossils have been found in the Los Alamitos and the La Colonia Formations of Argentina.

The original specimen of Reigitherium was a fragmentary single molar tooth, with a lot of the surface detail damaged.

[1] Ten years later, Pascual et al. argued that it was a docodont based on the wear patterns they interpreted on the teeth.

[4] More complete fossils have now supported this analysis[2] A recent phylogenetic study finds it to be the sister taxon to Peligrotherium.

[2] Although the latter is much larger than Reigitherium, they share many tooth and skull characteristics that indicate they are closely related.