Background extinction due to species specialization? Insights from a high-resolution Jurassic ammonoid case study (Dactylioceratidae)

The extinction of clades outside mass extinction events remains an understudied aspect of evolutionary dynamics. This study examines the Dactylioceratidae, an ammonite family that disappeared during the Early Jurassic, outside a recognized mass extinction event. By using high-resolution taxonomic (species-level) and temporal (sub-chronozone) data, we assess its evolutionary trajectory, from diversification to extinction. Our analysis reveals that Dactylioceratidae experienced an initial expansion in diversity and geographic range, followed by increased specialization. Morphological disparity and diversity peaked before a sharp decline, suggesting a possible link between ecological specialization and extinction risk. This pattern aligns with hypotheses proposing that over-specialization limits adaptability, leading to extinction under background conditions. In contrast to mass extinctions driven by sudden catastrophic events, background extinctions may be influenced by gradual ecological changes and evolutionary constraints. By comparing the case of Dactylioceratidae with broader ammonoid trends, this study provides insights into long-term extinction mechanisms. These findings are relevant for understanding both past and present biodiversity crises, shedding light on how species’ evolutionary strategies impact their survival over time.