 The late Cretaceous period, characterized by high CO2 levels and elevated temperatures, saw a flourishing of calcareous dinoflagellate cysts, c-dinosists, and calcifying plankton worldwide, with an ACME coinciding with the highest recorded seawater surface temperatures. This study examines the potential applicability of c-dinosists as a proxy for paleoenvironmental conditions based on their assemblage changes plotted against four aminiferal occurrences and microfaces analysis, using material extracted from the upper Tyronian chock in western Ukraine. An inverse correlation was observed between species diversity and the number of c-dinosus specimens, with nutrient availability gradients determining important changes in their distribution. These trophic changes were likely caused by eustatic c-level fluctuations and subhercenian tectonic activity leading to changeable nutrient inputs from nearby land. This article was authored by Agnieszka Sijerj, Sofia DeBicca, and Andriy Poboreskiy. We are article.tv, links in the description below.