A new early Permian actinopterygian assemblage shows environmental controls on the distribution of Paramblypterus (Intra-Sudetic Basin, Poland)

Abstract

Amblypteridae are ray-finned fish particularly common in late Carboniferous and early Permian vertebrate assemblages. We describe a rich new fish assemblage from the Poland-Czechia borderland, composed of only one species of amblypterid: Paramblypterus rohani. The analysis of articulation and completeness of the individuals unearthed shows that most of them underwent two, strongly different taphonomic histories. The first is represented by highly articulated and complete specimens buried close to their death site. Their decomposition took place mainly at the bottom of a deep lake with low hypolimnic temperature and bottom hypoxia. The second is represented by highly disarticulated and incomplete specimens, for which the bloat and float mechanism appears to be the main driver of decomposition. The results obtained suggest that thermal conditions in the former reservoir were seasonally varying. Moreover, the mass occurrence of amblypterids in environments largely touched by hypoxia shows that they were efficient open-water predators, which contrasts with previous ecomorphological studies of this group. The stratigraphic position of the assemblage studied remains unclear due to conflicting biostratigraphic and field data. The most parsimonious resolution of this ambiguity comes through considering the occurrence of various amblypterid species in the Intra-Sudetic Basin as controlled by environmental factors rather than by evolution.