The stratotype region of the Ryazanian stage is located in the Oka River Basin near Ryazan, Central Russia. Since ammonites are very well studied here, we investigated other groups of macrofossils. We report a large n...The stratotype region of the Ryazanian stage is located in the Oka River Basin near Ryazan, Central Russia. Since ammonites are very well studied here, we investigated other groups of macrofossils. We report a large number of bivalve genera: Arctica, Astarte, Buchia, Camptonectes, Chlamys, Ctenostreon, Entolium, Gomomya, Gresslya, Hartwellia, Lima, Meleagrinella, Modiolus, Oxytoma, and Pleuromya. The belemnites are represented by two cylindroteuthidid genera, Acroteuthis and Liobelus. In addition, brachiopods (Rhynchonellidae and Terebratulidae) and unidentifiable gastropod fragments have been revealed. The highest taxonomic diversity of macrofauna is observed in the Surites spasskensis ammonite Zone.展开更多
The stratigraphic record shows a considerable decrease in ammonoid taxonomic diversity and distinct changes of ammonite shell morphology toward end of the Jurassic in the Central Russian Basin. By the end-Volgian, amm...The stratigraphic record shows a considerable decrease in ammonoid taxonomic diversity and distinct changes of ammonite shell morphology toward end of the Jurassic in the Central Russian Basin. By the end-Volgian, ammonites were represented by only two genera, belonging to a single family Craspeditidae, which differ markedly from previous ammonite families in their shell form. The end-Jurassic decrease in ammonoid biodiversity started in the mid-Volgian and is mainly correlated with shallowing of the shelf.展开更多
文摘The stratotype region of the Ryazanian stage is located in the Oka River Basin near Ryazan, Central Russia. Since ammonites are very well studied here, we investigated other groups of macrofossils. We report a large number of bivalve genera: Arctica, Astarte, Buchia, Camptonectes, Chlamys, Ctenostreon, Entolium, Gomomya, Gresslya, Hartwellia, Lima, Meleagrinella, Modiolus, Oxytoma, and Pleuromya. The belemnites are represented by two cylindroteuthidid genera, Acroteuthis and Liobelus. In addition, brachiopods (Rhynchonellidae and Terebratulidae) and unidentifiable gastropod fragments have been revealed. The highest taxonomic diversity of macrofauna is observed in the Surites spasskensis ammonite Zone.
基金Supported by Program of the Presidium of the Russian Academy of Sciences "Origin of the Biosphere and the Evolution of Geo-biological Systems"
文摘The stratigraphic record shows a considerable decrease in ammonoid taxonomic diversity and distinct changes of ammonite shell morphology toward end of the Jurassic in the Central Russian Basin. By the end-Volgian, ammonites were represented by only two genera, belonging to a single family Craspeditidae, which differ markedly from previous ammonite families in their shell form. The end-Jurassic decrease in ammonoid biodiversity started in the mid-Volgian and is mainly correlated with shallowing of the shelf.
