Since its appearance on land in the early Paleozoic, life has conquered the continents with astonishing diversity. From the deepest caves to the atmosphere, numerous evolutionary innovations such as active flight or seeds paved the way for life beyond water. However, we still have a rough idea of the timelines of terrestrialization, mainly because fossil evidence remains patchy. It is therefore crucial to know the age and taphonomy of the few finds well. One such example is Tridentinosaurus antiquus, Italy’s oldest fossil reptile from the lower Permian Athesian Volcanic Group, Southern Alps. This specimen potentially enlightens the earliest ecosystems that coped with extensive volcanism, but its stratigraphic context is barely referenced. We clarify the provenience, age, fossilization and paleoecological meaning of T. antiquus using sampling-history review, field mapping, mineral chemistry and U-Pb radioisotopic dating. Accordingly, rock petrography and biotite composition prove that a crystal-rich, monotonous intermediate tuff from the Regnana Formation at Stramaiolo, Northern Italy, is the host rock of T. antiquus. Biotite crystallization in both field samples and the rock attached to the fossil yield values of 670±17°C and 1.7–2.0 kbar close to the granite solidus, strengthening a common magmatic history. The tuff formed from hot, diluted pyroclastic density currents that filled a paleo-valley between small volcanoes around 275 Ma. T. antiquus, hence, is par-autochthonous and truly inhabited the volcanic landscapes. Along with fossil plants and other similar taphocoenoses worldwide, this fossil documents the presence of differentiated ecosystems in late Paleozoic volcanic environments.