Ammonoids (Crioceratitinae, Hauterivian) from the Austral Basin, Chile

Abstract

Abstract. The low diversity of the Austral Basin ammonoid faunas was traditionally associated with a high degree of endemism. However, as reported herein, the ammonoids belonging to the Family Ancyloceratidae, Subfamily Crioceratitinae have affinities with European forms. Therefore, the Hauterivian ammonoids of the Austral Basin represent a mixture of endemic (Favrella Douvillé), with typical Tethyan examples (Hemihoplites Spath, Crioceratites Léveillé), and faunas that are characteristic of Northwestern Europe on the margins of the Boreal realm (Protaconeceras Casey, Aegocrioceras Spath), although the endemic forms dominate in number of specimens. The following species are described here: Aegocrioceraspatagonicum sp. nov. Aguirre-Urreta, Crioceratites (C.) apricum (Giovine) and Crioceratites sp. aff. C. (C.) schlagintweiti (Giovine). This rare and localized appearance of taxa of the Northern Hemisphere suggests periods of sea level rise that permitted widespread migration from this region to peripheral basins. Resumen. AMONOIDEOS (CRIOCERATITINAE, HAUTERIVIANO) DELACUENCA AUSTRAL, CHILE.La baja diversidad de las faunas de amonoideos de la cuenca Austral ha sido tradicionalmente asociada a su alto grado de endemismo. Sin embargo, aquí se describe una fauna de amonoideos de la Familia Ancyloceratidae, Subfamilia Crioceratitinae que muestra afinidades con formas europeas. De este modo, los amonoideos hauterivianos de la cuenca Austral representan una mezcla de géneros endémicos (Favrella Douvillé), con típicos ejemplos tethyanos (Hemihoplites Spath, Crioceratites Léveillé) y faunas características del noroeste de Europa en los márgenes del reino Boreal (Protaconoceras Casey, Aegocrioceras Spath), aunque las formas endémicas dominan en número de ejemplares. Se describen las siguientes especies: Aegocrioceraspatagonicum sp. nov. Aguirre-Urreta, Crioceratites (C.) apricum (Giovine) y Crioceratites sp. aff. C. (C.) schlagintweiti (Giovine). Esta rara y localizada aparición de taxones del Hemisferio Norte sugiere períodos de nivel del mar global alto, lo que habría permitido la migración desde esta región a cuencas periféricas.