Journal of Paleontology, page 1 of 11 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2018.59 Ascocerid cephalopods from the Hirnantian?–Llandovery stages of the southern Paraná Basin (Paraguay, South America): first record from high paleolatitudes M. Cichowolski,1,2 N.J. Uriz,3 M.B. Alfaro,3 and J.C. Galeano Inchausti4 1Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias Geológicas, Área de Paleontología, Ciudad Universitaria, Pab. 2, C1428EGA, Buenos Aires, Argentina 〈
[email protected]〉 2CONICET-Universidad de Buenos Aires, Instituto de Estudios Andinos “Don Pablo Groeber” (IDEAN), Buenos Aires, Argentina 3División Geología del Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina. 〈
[email protected]〉, 〈
[email protected]〉 4Ministerio de Obras Públicas y Comunicaciones de Paraguay, Asunción, Paraguay 〈
[email protected]〉 Abstract.—Ascocerid cephalopods are described for the first time from high paleolatitudes of Gondwana. Studied material was collected from the Hirnantian?–Llandovery strata of the Eusebio Ayala and Vargas Peña formations, Paraná Basin, southeastern Paraguay. The specimens are poorly preserved and were questionably assigned to the sub- family Probillingsitinae Flower, 1941, being undetermined at genus and species rank because diagnostic characters are not visible. A particular feature seen in our material is the presence of both parts of the ascocerid conch (the juve- nile or cyrtocone and the mature or brevicone) joined together, which is a very rare condition in the known paleonto- logical record. The specimens are interpreted as at a subadult stage of development because fully grown ascocerids would have lost the juvenile shell.