|mhorn||Дата: Sunday, 11.12.2011, 22:12 | Сообщение # 1|
|Schweigert G., Boursicot P.Y., Moor E. (2011) Granulochetoceras: ein Exot unter den Juraammoniten // Fossilien. Hft.5. S.280-287. |
The enigmatic ammonite genus Granulochetoceras Geyer, 1961, was recently recognized as a separate lineage of Strigoceratidae which splitted off from Strigoceras s. str. in the Bajocian. Granulochetoceras exhibits a keel undulating in its vertical axis, a steep umbilical wall, and a lateral furrow bordered by rows of nodules. Records of this genus are extremely rare. The stratigraphically oldest species is Granulochetoceras oppeliisculptum Schweigert et al. from the Garantiana Zone of Spain. Here we present newly collected material from the late Callovian Athleta Zone of France and from the early Kimmeridgian Platynota and Hyselocyclum zones of Switzerland, besides some further specimens from South Germany. The corresponding microconchs are not clearly identified yet, but there are some candidates. Granulochetoceras gave rise to Cymoceras in the early Kimmeridgian. This short phyletic twig became extinct in the higher part of the Hypselocyclum Zone with Cymaceras perundatum Wegele. Another possible offshoot of Granulochetoceras is “Ochetoceras” ex gr. canaliferum (Oppel).
Middle Jurassic - Lower Cretaceous ammonites & aptychi