Infrazonal Ammonite Biostratigraphy, Paleobiogeography and Evolution of Volgian Craspeditid Ammonites

Autor: Mikhail A. Rogov
Rok vydání: 2020
Předmět:
Zdroj: Paleontological Journal. 54:1189-1219
ISSN: 1555-6174
0031-0301
DOI: 10.1134/s0031030120100068
Popis: Data on the evolutionary and biogeographical differentiation features of the Volgian ammonites of the family Craspeditidae are summarized, an updated scheme of the Panboreal correlation of the terminal part of the Middle Volgian and Upper Volgian is proposed. The new Lambecki and Surlyki zones, as well as the surlyki, margaritae and discoides biohorizons are recognized. The diagnoses of the genera and subgenera of Volgian craspeditids are emended. All subfamilies of this family that existed at the end of the Middle Volgian and Late Volgian are characterized by a weakened ornamentation and a general tendency towards decrease in the size of the shells over time. Subcraspeditins and garniericeratins are characterized by a gradual decrease in the relative width of the whorls and umbilicus over time, while craspeditins in most lineages show a clear tendency to increase the relative thickness of the whorls. The taxa that inhabited the Middle Russian Sea show a direct correlation between the relative abundance of representatives of different subfamilies and the rate of their evolution, but in other regions this pattern is not observed. Volgian craspeditids are characterized by a high degree of endemism. Despite a constant exchange of faunas between the main evolutionary centers, only at the very end of the Late Volgian did the ammonite associations of most of the studied regions profoundly change due to massive introduction of immigrant taxa.
Databáze: OpenAIRE
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