The coincidence of a diverse vertebrate assemblage with a high-precision geochronology and lithostratigraphy in Petrified Forest National Park (Arizona, USA) allows Bayesian quantification of the dynamics of a Late Triassic vertebrate extinction and replacement, the Adamanian/Revueltian (A/R) faunal turnover. This approach uniquely identifies probabilities for the tempo of the replacement of the Adamanian assemblage by that of the Revueltian, precisely tracking the turnover. While the method does not designate the moment of extinction, there is a negligible probability that all Adamanian extinctions, as well as all Revueltian originations, are synchronous. A protracted A/R turnover is incompatible with the geologically instantaneous Manicouagan impact (215.4 ± 0.20 Ma; Québec, Canada) as a dominant causal mechanism. This analytical framework constitutes a flexible means of reconstructing biotic turnover in a variety of deep time contexts.