The Central Paratethys Sea, a former marine environment in Central and Southeastern Europe, was a biodiversity hotspot during the Miocene, particularly during the Miocene Climatic Optimum (MCO, ~17–14 Ma). This period saw a significant increase in marine biodiversity, driven by tectonic reorganization and favorable climatic conditions. The tectonic changes created an archipelago-like landscape, while the MCO supported the development of coral reefs, enhancing habitat diversity and species richness. However, the Middle Miocene Climate Transition (MMCT, ~14–13 Ma) led to a dramatic decline in biodiversity, with about 67% of species disappearing. This decline was particularly severe for corallivorous gastropods and deep-water faunas, which were affected by changing circulation patterns and lower sea levels. The fragmentation of the Paratethys Sea during this period increased biogeographic turnover, with the most significant decline occurring during the Sarmatian when bottom water dysoxia eradicated deep-water fauna. The study presents a georeferenced dataset of 859 gastropod species, highlighting the Central Paratethys as a marine biodiversity hotspot. The region's biodiversity was influenced by tectonic activity, climate, and the establishment of coral reefs. The study also discusses the impact of the MMCT on marine ecosystems, including the collapse of zooplankton in surface waters and the decline of deep-water species. The Central Paratethys Sea, though a biodiversity hotspot, was geologically short-lived, lasting no more than 3 million years, and did not sustain long-term biodiversity like modern hotspots such as the Coral Triangle. The study underscores the role of climate and geodynamics in shaping marine biodiversity.The Central Paratethys Sea, a former marine environment in Central and Southeastern Europe, was a biodiversity hotspot during the Miocene, particularly during the Miocene Climatic Optimum (MCO, ~17–14 Ma). This period saw a significant increase in marine biodiversity, driven by tectonic reorganization and favorable climatic conditions. The tectonic changes created an archipelago-like landscape, while the MCO supported the development of coral reefs, enhancing habitat diversity and species richness. However, the Middle Miocene Climate Transition (MMCT, ~14–13 Ma) led to a dramatic decline in biodiversity, with about 67% of species disappearing. This decline was particularly severe for corallivorous gastropods and deep-water faunas, which were affected by changing circulation patterns and lower sea levels. The fragmentation of the Paratethys Sea during this period increased biogeographic turnover, with the most significant decline occurring during the Sarmatian when bottom water dysoxia eradicated deep-water fauna. The study presents a georeferenced dataset of 859 gastropod species, highlighting the Central Paratethys as a marine biodiversity hotspot. The region's biodiversity was influenced by tectonic activity, climate, and the establishment of coral reefs. The study also discusses the impact of the MMCT on marine ecosystems, including the collapse of zooplankton in surface waters and the decline of deep-water species. The Central Paratethys Sea, though a biodiversity hotspot, was geologically short-lived, lasting no more than 3 million years, and did not sustain long-term biodiversity like modern hotspots such as the Coral Triangle. The study underscores the role of climate and geodynamics in shaping marine biodiversity.