Article: Ammonites of Tethyan ancestry in the early Lower Cretaceous of north-west Europe
Early Lower Cretaceous (Berriasian-Hauterivian) ammonite faunas in north-west Europe were predominantly of boreal origin. However, during Valanginian and Hauterivian times there was strong Tethyan influence. The most sharply defined immigration horizons (earliest Valanginian, early late Valanginian and mid Hauterivian) coincide with significant transgressions. Some species came singly or in small numbers, while others migrated in large numbers to evolve into thriving populations which sometimes gave rise to endemic genera. All the following genera are of Tethyan origin and are reviewed here; species descriptions are given for those genera marked with an asterisk: Phylloceras, Phyllopachyceras, Lytoceras s. 1., Juddiceras*, Aegocrioceras, Crioceratites* (subgenera Crioceratites* and Paracrioceras*), Bochianites*, Protaconeceras*, Olcostephanus, Subastieria, Parastieria, Valanginites, Saynoceras*, Platylenticeras, Thurmanniceras?*, Neocomites (subgenera Neocomites* and Teschenites*), Varlheideites, Karakaschiceras*, Neohoploceras*, Dicostella*, Endemoceras, Distoloceras, Acanthodiscus, Leopoldia, Saynella, Oosterella*, Subsaynella* and Spitidiscus. Two new species are described: Crioceratites (Paracrioceras) spathi and Dicostella germanica. In conjunction with records of boreal ammonites in France, these occurrences allow close correlation of north-west European and Tethyan zonal schemes.