6533b7ddfe1ef96bd1273686

RESEARCH PRODUCT

Problems in the identity of "Crioceras" barremense Kilian, 1895 (Ancyloceratida, Late Barremian), and their proposed resolution

subject

description

17 pages; The study of "Crioceras" barremense KILIAN was undertaken as a part of the revision of the Hemihoplitidae. This species was considered "classic" and has been used as the index of an Upper Barremian subzone; this usage raises a number of problems. The type specimen from Tyrol was a fragment described and illustrated by UHLIG as Crioceras sp. ind. aff. roemeri. This specimen could not be retrieved, and a topotype could not be collected. Our study revealed that there is both a biostratigraphic hiatus and important differences between conceptions of this species: (1) that ascribed UHLIG's type specimen (Upper Barremian, Tyrol), (2) KILIAN's concept of the specimen he found and named "Crioceras" barremense (probably a Camereiceras from the uppermost levels of the Vandenheckei Subzone or from the basal Sartousiana subzone of the Nauvin site, southeastern France) and (3) current interpretations of authors, who often synonymize the type specimen with Gassendiceras alpinum (d'ORBIGNY), which occurs in the middle of the Vandenheckei Subzone. So there is a real confusion concerning the synonymy of "Crioceras" barremense. The age of UHLIG's type specimen is too imprecise and its preservation too fragmentary to be reliably identifiable, because the same morphology and ornamentation exist in several species of other genera. Therefore, we recommend the use of the species "Crioceras" barremense KILIAN be avoided, in particular as an index, along with that of the genus Barrancyloceras VERMEULEN for which "C." barremense is used as reference. Some species formerly assigned to this genus have been referred to the genus Gassendiceras BERT et alii. Consequently, we also recommend the Barremense auctorum Subzone be renamed the Alpinum Subzone (new) [index-species: Gassendiceras alpinum (d'ORBIGNY)], without changing its limits as currently defined. The lower limit of this subzone is indicated by the first occurrence of Gassendiceras alpinum (a new biohorizon, introduced here), a common, easily identifiable species with a well-defined stratigraphic range.