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.
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RBINS Staff Publications 2021
The Quercy Phosphorites are a set of Eocene-Oligocene deposits from South-West France that yielded numerous vertebrate fossils, including amphibians, mostly as isolated bones. However, in 1873, several exceptional amphibian specimens were discovered, with the external surface of the unmineralized tissues preserved, and were commonly referred as “mummies”. In the 19th century, they were described without any knowledge of their internal anatomy. Since 2012, we have started scanning these “mummies”, revealing the preserved internal soft tissues and articulated skeleton. A first specimen was attributed in 2013 to Thaumastosaurus gezei and we here present our results from the tomography of a second “mummified” anuran, previously identified as Bufo servatus. The tomography showed a preserved articulated skeleton, and its osteological characteristics are similar to the first scanned anuran “mummy”, representing different ontogenetic stages. Both are now both attributed to Thaumastosaurus servatus nov. comb. The new anatomical information is used to assess the affinities of T. servatus, which appears to belong to the Pyxicephalidae, an African anuran clade. Thaumastosaurus thus represents both the oldest occurrence of this clade in the fossil record and its first occurrence outside of Africa. Its presence in Europe highlights a faunistic exchange with Africa during the Eocene, also documented for several clade of squamates. The presence of this African herpetofauna in Europe might be linked to the warmer climate during the Eocene. However, most of this herpetofauna, including Thaumastosaurus, disappeared from the region around an extinction event (named the “Grande Coupure”) that took place around the Eocene/Oligocene transition (~34 Ma).
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RBINS Staff Publications 2021
