The ammonites of the family Perisphinctidae from the Plicatilis Zone (lower Middle Oxfordian) of the Polish Jura Chain (Central Poland); their taxonomy, phylogeny and biostratigraphy

Abstract

The Plicatilis Zone of the Submediterranean Middle Oxfordian is redefined and subdivided into three subzones: the Paturattensis Subzone, the Ouatius Subzone and the Arkelli Subzone. Their boundaries are defined by the appearance of the successive perisphinctid species referred to a Kranaosphinctes-Otosphinctes lineage. Correlation with other lower Middle Oxfordian zonations is provided. Classification of the studied ammonites is based on the morphological variability in the successive perisphinctid assemblages. The species are assigned to three genera: Perisphinctes, Liosphinctes and Neumannia gen. nov. Microconchs of Neumannia gen. nov. and of Perisphinctes trifidus (SOWERBY) are described for the first time. The type species of the subgenus Arisphinctes, P. ariprepes (BUCKMAN), is reassigned to the subgenus Kranaosphinctes BUCKMAN, and thus Arisphinctes is treated as a younger synonym of Kranaosphinctes; Perisphinctes plicatilis (SOWERBY) and Perisphinctes laevipickeringius ARKELL are reinterpreted and reassigned to the genus Liosphinctes BUCKMAN. Two new chronosubspecies, Perisphinctes ouatius ouatoides and Perisphinctes arkelli wysokae of the subgenus Otosphinctes, are distinguished. The Kranaosphinctes-Otosphinctes lineage gives rise to the Perisphinctes-Dichotomosphinctes lineage at the boundary between the Plicatilis and Transversarium zones. The two other lineages, one of P. trifidus (a possible offshoot from the Kranaosphinctes-Otosphinctes lineage), and the other of the genus Liosphinctes, disappear in the upper Arkelli Subzone of the Plicatilis Zone. Mediterranean roots for all of the three lineages are suggested. The fourth lineage, of Neumannia gen. nov., appears in the upper Arkelli Subzone of the Plicatilis Zone as a consequence of an immigration event from the Mediterranean area.