Extreme diversity of decapod crustaceans from the mid-Cretaceous (late Albian) of Spain: Implications for Cretaceous decapod paleoecology

Thirteen decapod crustacean species, eight of which are new, from the mid-Cretaceous (late Albian) limestones of the Koskobilo quarry in northern Spain are described, illustrated, and discussed. They include: Graptocarcinus texanus; Navarrara betsieae gen. nov., sp. nov.; Acareprosopon bouvieri n. comb.; Laeviprosopon hispanicum sp. nov.; L. planum sp. nov.; L. edoi sp. nov.; L. crassum sp. nov.; Viaia robusta; Cretamaja granulata gen. nov., sp. nov.; Koskobilius postangustus gen. nov., sp. nov.; Navarrahomola hispanica; Glytodynomene alsasuensis; and Albenizus minutus gen. nov., sp. nov. Cretamaja and Koskobilius represent the oldest known spider crabs. In total, 36 species are now known from the Koskobilo locality based on 1078 specimens. To discover the magnitude of the diversity of the decapod fauna of Koskobilo, a comprehensive overview of decapod-rich localities and formations from the Cretaceous worldwide was compiled. It appears that Koskobilo is the most diverse decapod fauna from a single locality currently known from the Cretaceous. A rarefaction analysis shows that the maximum number of species is nearly reached. The number of genera, 26, is also unsurpassed for the Cretaceous. Forty-two species are found from localities within the Eguino Formation to which sediments from the Koskobilo quarry are ascribed, which is also unprecedented for a single formation within the Cretaceous. Evidence suggests that the most diverse decapod faunas from the Cretaceous are found in coral-associated limestones. This is consistent with evidence from the Recent, where decapod diversity is high in coral reefs compared to other habitats. This also suggests that the decapod peak diversity in Koskobilo is largely ecological in nature and not caused by a preservational bias. This is one of the most comprehensive studies on Cretaceous decapod diversity so far. Field work in coral-associated strata is expected to yield more decapod-rich faunas.