The perisphinctid genus Prososphinctes Schindewolf (Ammonoidea, subfamily Prososphinctinae nov.): an indicator of palaeoecological changes in the Early Oxfordian Submediterranean sea of southern Poland
The perisphinctid genus Prososphinctes Schindewolf is monographed with regard to its palaeoecological and biostratigraphic value, palaeobiogeographic dispersion, phylogeny and systematics. The conclusions are based on new ammonite collections from the Lower Oxfordian Jasna Góra
beds, Submediterranean neritic sea, southern Poland. Bukowski's (1887) species (consociatus, claromontanus) are re-evaluated using topotypes from the Czństochowa region and their types – first illustrated here – kept in Vienna (Austria). Brochwicz-Lewiński's
(1981) species are re-interpreted and re-illustrated. New species is erected (polelum). The genus ranges in Poland from the Mariae up to the middle Cordatum Zone (Costicardia Subzone), with sporadic occurrences higher up. The new subfamily Prososphinctinae is erected. Besides incorporating
Prososphinctes, it groups successive Oxfordian genera (Liosphinctes, Platysphinctes, Larcheria, and allies), which are considered to form a lineage. This study supports the Cuban perisphinctid subfamily Vinalesphinctinae as being an offshoot of the Prososphinctinae
lineage. The bed-by-bed analysis of Prososphinctes-bearing ammonite assemblages using quantitative methods is designed to identify and time-correlate percentage changes in indigenous Perisphinctidae and adventive (Boreal or Mediterranean) ammonite families. The paper links these changes
with the establishment of new open marine sea-ways (determined by tectono-eustatic factors), and their postulated impact on the Submediterranean ammonite habitat. Prososphinctes is regarded as a precise indicator of these changes due to its pronounced fluctuations in abundance from
the bottom to the top of the sections. The present study demonstrates that the early stages of dispersion and diversification of the perisphinctid stock in the Early-Middle Oxfordian were closely related to habitat fluctuations and determined by biological mechanisms (opportunistic in Prososphinctes
versus equilibrial in Perisphinctes) and interactions (competition).
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