This study reports the oldest record of cephalopods from the Central Andean Basin. Numerous small ellesmeroceratids were collected from the Alfarcito Member of the Santa Rosita Formation in the Quebrada de Arenal/Trancas, Jujuy, Argentina. The cephalopods were found associated with the trilobite Kainella meridionalis, indicating an early Tremadocian (Tr1) age. They are not exceeding 20 mm in length and have slightly curved apices and very short chambers. The siphuncle is marginal and rather big, with straight and ortho- to hemichoanitic septal necks. Based on these features, an assignment to the Family Ellesmeroceratidae is suggested.The oldest record of cephalopods worldwide is from the Jiangshanian Stage (Furongian Series) of North China. In the early Stage 10, the cephalopod diversity and abundance increased. They are also known from Laurentia and other isolated or dubious localities (e.g., Siberia, Kazakhstan). By the end of the Cambrian, cephalopods underwent an important crisis, leading to the extinction of 95% of the existing genera. Only two of the forty known genera from the Furongian survived this event.Cephalopods from the early Tremadocian (Tr1) are not abundant or widespread but are dominated by ellesmeroceratids. So far, they were unknown from mid to high paleolatitude basins. This is the first record from a temperate water region and the oldest from the Central Andean Basin. Contrary to coetaneous cephalopod assemblages from Laurentia, this association seems to be of very low diversity. One particular trait makes it outstanding: the very small size of the specimens, which reminds those known from the late Cambrian.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vaccari, Norberto Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Vaucher, R.. University Fraser Simon; CanadáFil: Waisfeld, Beatriz Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaReunión de Comunicaciones de la Asociación Paleontológica ArgentinaLa PlataArgentinaAsociación Paleontológica ArgentinaUniversidad Nacional de La Plata. Facultad de Ciencias Naturales y Muse
