Microlestes antiquus was named by Plieninger (1847). Its type specimen is Stuttgart Naturalienkabinet specimens, a set of teeth (two minute teeth), and it is a 3D body fossil. Its type locality is Schlösslesmühle bone bed, which is in a Rhaetian terrestrial horizon in the Exter Formation of Germany.

It was recombined as Thomasia antiqua by , Simpson (1928), Huene (1940), Kuhn (1971), Hahn (1973), Butler and Macintyre (1994), Kielan-Jaworowska et al. (2004).