Echioceratidae from Raricostatum Zone (Raricostatum and Macdonnelli subzones) in NW Iberia

Abstract This study examines 535 ammonite specimens from the main reference sections of Asturian, Basque-Cantabrian, and Lusitanian basins (NW Iberia) that characterise the Raricostatum and Macdonnelli subzones of the Raricostatum Zone (Sinemurian, Lower Jurassic). The fauna is dominated by the family Echioceratidae (89.9%), particularly Echioceras quenstedti , Echioceras raricostatoides and Echioceras raricostatum in the lower Raricostatum Subzone, and Paltechioceras boehmi , Paltechioceras favrei , Paltechioceras rothpletzi , and Paltechioceras bavaricum in the upper part. The Macdonnelli Subzone is characterised by Leptechioceras meigeni , and Leptechioceras macdonnelli , with the record of Paltechioceras charpentieri , as well as Leptechioceras ( Neomicroceras ) commune , Leptechioceras ( Neomicroceras ) aff. commune , and Leptechioceras ( Neomicroceras ) sparsicosta in northern Spain. These taxonomical identifications enabled a precise biochronostratigraphic framework and strong correlation with the northwestern European Province. The presence of Paltechioceras species shared with both the Mediterranean Province and the Pacific region suggests the possibility of sporadic connections, potentially facilitated by the Hispanic Corridor. The restricted palaeobiogeographic distribution of Echioceras and Leptechioceras , compared to the broad distribution of Paltechioceras , can derive from significant palaeobiology and phenotypic diversity. The identification of Leptechioceras ( Neomicroceras ) in the Basque-Cantabrian Basin slightly expands the previously described distribution of this subgenus. These findings underscore the role of ammonite species in refining biochronostratigraphic divisions and highlight the influence of palaeoenvironmental or palaeobiological factors on the evolution and distribution of Echioceratidae.