In the 19th century, natural mummies of amphibians were discovered in the Quercy Phosphorites. The specific collection site was never formally reported, which hampers precise dating of these specimens. Still, the name Bufo servatus was erected based on the external morphology of one of the mummified specimens. A tomography of a similarly preserved specimen revealed a preserved skeleton, soft tissues and gut contents. We analyze here the holotype of Bufo servatus using CT-scanning in order to investigate its potentially preserved internal features. Like the previous specimen, a subcomplete articulated skeleton was identified in the B. servatus holotype. Surprisingly, this skeleton is almost identical to that of Thaumastosaurus gezei, an Eocene anuran from Western Europe to which other specimens from this mummy series were previously assigned. The few differences between the specimen skeletons highlight ontogenetic and intraspecific variations, making T. gezei a junior synonym of B. servatus and creating the new combination Thaumastosaurus servatus. Given its association with previously described Quercy specimens, this redescribed anuran is probably from the same time interval as T. gezei. Previous phylogenetic analyses assigned T. servatus to Ranoides, with natatanuran affinities. Using data from this newly described specimen, we tested here further its taxonomic affinities. Our analyses confirm this position, and formally identify T. servatus as a Natatanuran member of Pyxicephalidae (currently endemic of equatorial Africa) and more precisely, a stem-Pyxicephalinae. This result confirms the origin of Thaumastosaurus, a member of the African herpetofauna occupying Western Europe before the Grande Coupure at the Eocene/Oligocene transition.