Preprint: Paleoecological insights from coprolites and their inclusions from the Permian Rio do Rasto Formation, Brazil

Coprolites have provided valuable insights into paleoecological relationships, such as predation and parasitism, as well as taphonomic and paleoenvironmental conditions. However, few studies have focused on coprolites from the Rio do Rasto Formation, despite their abundance in this formation. Here, we analyze and describe 97 coprolites from 11 sites within the Rio do Rasto Formation (middle/upper Permian) of Paraná Basin (southern Brazil). External and internal features were examined, classifying the material into four morphotypes: heteropolar (12%), amphipolar (11%), indeterminate spiral (40%) and non-spiral (37%). Alimentary inclusions, such as fish scales, teeth, bone fragments, plants and insect wing, were identified in nearly all specimens. Additionally, microorganisms and parasites were preserved within the fecal matrix, including bacilli bacteria, Actinomycete biofilm, fungal hyphae and spores, Nostocales and Chroococcales cyanobacteria, and cestode eggs. The bacteria and fungi originated from the intestinal tract of the producer before the extrusion, while the cyanobacteria were ingested from the water where these animals lived in. The new occurrence of cestode eggs provide direct evidence of parasitism and corroborates the existence of this relationship from at least the Permian. The phosphatic composition of the coprolites, combined with bacterial and fungal activity, was crucial for preserving delicate organic remains (e.g., plant and insect wing) and organisms (e.g., parasites). These findings enhance our understanding of the producer diet, paleoecological interactions, and the microenvironment within the feces.