Current extinction rate in European freshwater gastropods greatly exceeds that of the late Cretaceous mass extinction

Freshwater ecosystems harbor disproportionately high biodiversity (about 70% of global species richness within just 1% of Earth’s surface) and provide key ecosystem services. Yet, freshwater biota are undergoing severe declines in richness and abundance due to habitat degradation and destruction, climate change, eutrophication, pollution, groundwater extraction, and invasive species. The current crisis is widely regarded as the onset of a sixth mass extinction, bearing similarities to the Cretaceous–Paleogene (K–Pg) event in its catastrophic nature and association with rising CO2 and global temperature. Previous estimates based primarily on freshwater vertebrates suggested relatively low freshwater losses (10–22%) at the K–Pg boundary, but vertebrates comprise only ~15% of freshwater species and may not represent overall freshwater biota. Freshwater gastropods are diverse, broadly distributed, have a strong fossil record, and are affected by threats representative of freshwater biodiversity as a whole, making them an appropriate model taxon. This study compiles and analyzes the European freshwater gastropod fossil record to quantify the magnitude, duration, and dynamics of extinction and subsequent recovery across the K–Pg boundary, and compares these results with predictions for near-future extinctions in Europe based on IUCN Red List data under a business-as-usual scenario.

Earlier work relying on freshwater vertebrate fossils reported comparatively modest K–Pg impacts in freshwater (10–22% species loss). These estimates likely underrepresent total freshwater biodiversity responses because vertebrates constitute only a small fraction of freshwater species. The discrepancy prompted reassessment using other taxa. Gastropods are well-suited due to their diversity, ecological breadth, and robust fossil record. The study leverages Europe’s particularly rich and well-studied fossil record and comprehensive conservation assessments to provide a more representative view of freshwater extinction dynamics.

Fossil dataset: The authors assembled locality-based freshwater gastropod occurrence data across Europe from the Jurassic to the Pleistocene, covering roughly the past 200 million years. The compiled dataset includes 24,759 fossil occurrences and 3,122 species, with extensive taxonomic vetting: doubtful records were excluded; recent revisions were applied; and species-level resolution was prioritized to avoid biases associated with genus-level analyses. Geographical scope includes Europe sensu lato (including Anatolia, the Caucasus, and adjacent Paratethys/Caspian realms), focusing on freshwater taxa with appropriate fossilization potential. Records were critically reviewed by stratigraphic specialists to minimize systematic and stratigraphic inconsistencies. Diversification inference: Speciation, extinction, and preservation rates were jointly inferred from fossil occurrence data using a Bayesian birth–death framework with time-varying rates. Sampling was modeled as a time-variable Poisson process to accommodate heterogeneous preservation through time and across species. Reversible-jump MCMC (RJ-MCMC) was used to infer temporal shifts in speciation and extinction. Very long MCMC chains were run, with burn-in discarded and effective sample sizes assessed (e.g., with R tools) to ensure convergence. Extinction magnitude across the K–Pg was quantified as the percentage of species that became extinct during the interval defined by detected shifts in the extinction rate. Future extinction projections: For extant European freshwater gastropods, conservation status data for 347 species were obtained from the IUCN Red List. To align with fossil comparability, species with very low fossilization potential (e.g., spring, subterranean, cave/karst specialists) were excluded in the primary analysis. Using a simulation framework (iucnSim-like tool), future transitions among IUCN statuses were modeled based on estimated transition rates to predict extinction risks over defined horizons (50, 80, and 100 years) and to estimate when a 75% extinction threshold (mass-extinction criterion) might be reached. Uncertainty was captured via repeated simulations to derive credible intervals.

- K–Pg impact severity: Extinction rates increased by more than one order of magnitude during the K–Pg, leading to a 92.5% loss of European freshwater gastropod species and a 9.5% loss of genera among those with fossils spanning the boundary. - Event duration and recovery: The extinction phase lasted about 5.47 Myr (66.9–61.4 Ma). A speciation pulse of similar magnitude accompanied the event. Speciation remained elevated for approximately 6.9 Myr after the extinction rate dropped, and diversification rates returned to Late Cretaceous background levels roughly 11.8 Myr after the onset (by ~55.1 Ma). - Long-term diversity trajectory: Mesozoic diversity shows a slow decline with pronounced changes near the Jurassic–Cretaceous boundary and Late Cretaceous; post-K–Pg recovery to Late Cretaceous levels took ~7.8 Myr, with a later Neogene peak linked to long-lived lakes. - Comparison with present: Predicted extinction rates for extant European freshwater gastropods are extremely high: 137.9 (131.6–144.1), 187.1 (173.3–184.0), and 197.3 (192.3–203.0) E/MSY over the next 50, 80, and 100 years, respectively—approximately three orders of magnitude higher than during the K–Pg event (reported as about −1.45 E/MSY in the figure context). Between 72 (20.8%) and 111 (31.9%) species are projected to go extinct within 50–100 years. The 75% extinction threshold could be reached by the year 2539 (95% CI: 2527–2551). - Genus-level robustness: Using genera yields a projected extinction rate of 107.18 (85.0–119.6) E/MSY over 100 years—lower than species-level but of the same order, supporting robustness of conclusions. - Historical context: Quaternary extinction rates rose above background (intermediate plateau), yet current projected rates are three to four orders of magnitude higher.

The findings overturn the notion—derived from vertebrate-only analyses—that freshwater ecosystems were relatively spared at the K–Pg. Instead, European freshwater gastropods suffered catastrophic losses (92.5% species extinction), exceeding even the global average across all biota (≈76%). This aligns freshwater gastropods with multiple marine and terrestrial clades known to have undergone severe K–Pg declines. While the European record is exceptional, whether this pattern generalizes globally remains uncertain given limited comparable datasets outside Europe and North America. The K–Pg event provides a relevant analog for today’s rapid, human-driven biodiversity crisis: both involve sudden, severe environmental perturbations coupled with warming. However, projected near-future extinction rates in European freshwater gastropods are vastly higher than those inferred for the K–Pg, indicating an even faster and potentially more devastating biodiversity decline if current trends persist. These results highlight the urgency for conservation interventions to avert a regional-scale mass extinction within centuries.

This study compiles an extensive European fossil record of freshwater gastropods and applies Bayesian diversification models to quantify extinction dynamics across the K–Pg boundary, revealing a 92.5% species loss and multi-million-year recovery dynamics. Projections based on IUCN data indicate that current and near-future extinction rates in Europe far exceed those of the K–Pg, with a potential to reach mass-extinction thresholds within the next few centuries. The work underscores the severity of the ongoing freshwater biodiversity crisis and the need for immediate, large-scale conservation action. Future research should expand comparable, quality-controlled fossil and conservation datasets to other continents to test global generality and refine temporal and taxonomic resolution of extinction and recovery dynamics.

- Geographic scope: Analyses are based on the European fossil record; global representativeness is uncertain due to limited comparable datasets elsewhere. - Fossil record resolution: Stratigraphic binning can obscure precise timing (e.g., onset of the extinction spike slightly predating the K–Pg boundary) and preservation biases may affect occurrence data. - Taxonomic uncertainties: Despite rigorous vetting, historical taxonomic issues and revisions may introduce residual uncertainty. - Extant data constraints: IUCN assessments are incomplete for some groups and regions; simulations depend on status transition rate estimates and exclude certain low-fossilization taxa to match fossil comparability, potentially underrepresenting total extant diversity at risk. - Model assumptions: Birth–death modeling and IUCN-based simulations rely on assumptions about preservation, sampling, and status transitions that may influence rate and timing estimates.