Thomasia hahni was named by Butler and Macintyre (1994). Its type specimen is the lower molar from the Middle Keuper of Halberstadt, Germany, described and figured by Hahn (1973), a tooth, and it is a 3D body fossil. Its type locality is Baerecke-Limpricht clay pit, Halberstadt (bed 18), which is in a Rhaetian floodplain claystone/sandstone in the Trossingen Formation of Germany.