Age and correlation of Late Triassic tetrapods from southern Poland

Abstract

Age assignments of Triassic tetrapod fossils can be achieved by direct reference to a scheme of Triassic land-vertebrate faunachrons (LVFs) that correlates Triassic tetrapod fossil assemblages to each other based solely on the tetrapod fossils. Correlation of Triassic tetrapod assemblages to the standard global chronostratigraphic scale (SGCS, the “marine timescale”) is a separate cross correlation between the vertebrate biochronology and marine biochronology that usually relies on other data (e. g., palynostratigraphy, magnetostratigraphy, radioisoto- pic ages) to be completed. Late Triassic tetrapod fossils in southern Poland are found at two stratigraphic positions, the Krasiejów and Lisowice levels. The tetrapod assemblage of the Krasiejów level is assigned to the early Adamanian LVF based primarily on the stratigraphic overlap of the phytosaur Parasuchus with the Adamanian index aetosaur Stagonolepis. The amphibians Cyclotosaurus and Gerrothorax, a Proterochersis-like turtle and the aetosaur Paratypothorax from the Lisowice level indicate it is assignable to the Revueltian LVF. Cross correla- tions to the SGCS are less definitive, but suggest that the Krasiejów level is late Carnian and the Lisowice level is early/middle Norian. However, this correlation of the Krasiejów level is confounded by disagreements over correlation of the marine Carnian–Norian boundary to nonmarine strata. Indeed, the possibility that the Krasiejów tetrapods fill a gap in the early Norian record of tetrapods merits consideration. Such difficulties emphasize the value of correlating tetrapod assemblages to each other using a land-vertebrate biostratigraphy/biochronology, instead of immediately attempting the more problematic correlation to the SGCS.