Revision and new data on the Coniacian ammonite genus Hemitissotia in the Iberian Peninsula (Spain and Portugal)

The types of the species of the Coniacian ammonite genus Hemitissotia Peron, 1897, identified in the Iberian Peninsula (Spain and Portugal), which are currently held in the Wiedmann (Universitat Tubingen, Germany) and Choffat (Instituto Geolgico e Mineiro, Portugal) collections, have been revised and refigured. New specimens of the taxa Hemitissotia ceadouroensis Choffat, 1898, Hemitissotia celtiberica Wiedmann, 1975b, Hemitissotia turzoi Karrenberg, 1935, Hemitissotia dullai (Karrenberg 1935) and Hemitissotia lenticeratiformis Wiedmann in Wiedmann and Kauffman, 1978 have also been presented. As results, H. celtiberica has been considered as a junior synonym of H. ceadouroensis, and the lectotype of this species and the neotypes of H. turzoi and H. dullai have been designated and figured. Additionally, the geographical and stratigraphical distributions of all of these species have been determined with precision, and several phylogenetic relationships between them have been identified, revealing morphologies that become progressively smaller and more depressed and ornamented (hydrodynamically less efficient), interpreted as an adaptative response to sea-level changes.