Limnic herpetofaunas of the Permian late-icehouse tropics: Insights from the Lochbrunnen Lake Unit (Oberhof, central Germany)

The Lochbrunnen Lake Unit (Oberhof Formation, Thuringian-Forest Basin) represents one of the youngest perennial-lake deposits of the European Permian and is key to understanding limnic ecosystem evolution in tropical Pangea. Based on two excavations, 126 temnospindyl specimens were anatomically documented, biometrically analyzed, taxonomically identified, and their embedding pelites lithologically and taphonomically characterized on a millimeter scale.

Most amphibians—mainly the branchiosaurids Apateon flagrifer and Melanerpeton arnhardti (90–95%) and the eryopid larvae of Onchiodon sp. (5–10%)—are preserved as articulated impressions with skin shadows, occurring in profundal and subordinate littoral facies. Five taphotypes reflect different preservation modes, often linked to microbial mats, anoxia, and sediment dynamics. Dorsoventral orientation predominates, while lateral burial is rare. The lake ecosystem comprised a full trophic web: microbial mats and algae (Perissothallus) as producers; bivalves, conchostracans, crustaceans, branchiosaurids, and Onchiodon larvae as consumers; and xenacanthid sharks and adult Onchiodon as top predators. The dominance of small branchiosaurids indicates ecological instability related to increasing aridification. Under these conditions, A. flagrifer appears as a generalist, while M. arnhardti shows possible adaptations (e.g., sclerotic rings, basibranchial morphology) to living in deep or oxygen-poor waters. Exceptional preservation of the amphibians likely resulted from anoxic events, microbial coverage, and rapid burial. The results document the various taphonomic pathways of amphibians in lakes and enlighten the impacts of late-icehouse environmental changes on low-latitude lake ecosystems.