Boreskov

PP‐26genera existing at that time, 7 were endemic. In the Roadian stage there existed 9 genera,whereas only 2 genera are known from the Wordian.At the American Realm ammonoids were moderately diverse: in the Asselian ‐ 31% a.g.,in the Sakmarian ‐ 26% a.g. Of 23 genera existing during that period, 8 appeared in the sameregion, whereas four are endemic. From the very beginning of the Middle Permian therelative diversity began increasing: in the Roadian it was 27% a.g., in the Wordian 38% a.g.,and in the Capitanian 80% a.g. Almost all new genera were aboriginal.At the Australian Realm ammonoid occurrences are known from the Sakmarian‐Capitanian beds. The Sakmarian ammonoids ‐ 8 genera (19% a.g.), all these were immigrantsfrom other regions. 7 genera existed in the Artinskian (12% a.g.), Kungurian (6%). 4 generaare recorded in the Roadian; the composition of these assemblage is interesting: 2cosmopolitan genera, 1 ‐ Tethyan, and one is a characteristic taxon of the Arctic Realm.In the Permian, there were several separate centers of morphogenesis within thePaleotethys Ocean (Pamir, Timor, Sicily, South China), which suggests that these basins werefrom time to time isolated within this realm. Basins of Pamir, Afghanistan, Southwest China,Thailand, Malaysia, and Timor were connected to each other throughout the Early Permian,with a more intense exchange in the second half. At the beginning of the Middle Permianbasins of Sicily, Tunisia, Oman, Iraq, the Crimea, Greece, and Croatia could freely exchangetheir pelagic faunas, especially in the Wordian. Apparently, relatively stable connectionsexisted between the above regions and Timor. A restricted exchange of faunas occurredbetween the eastern part of the Paleotethys and the American Realm. At the end of the LatePermian, the South China, Far East‐Japan, and Iran‐Transcaucasia basins were inhabited byrelated ammonoid communities, which apparently resulted from similar environments, closegeographic location, and migratory pathways.Climatic fluctuations of the Permian period were a significant factor influencing bothmorphological and paleobiogeographical changes. A wide distribution of ammonoid faunasat the end of the Artinskian coincided with an episode of global warming, whereas a sharpdecrease in the ranges and increased provincialism at the end of the Permian coincided withthe general trend towards aridization and prominent cooling. A considerable warming at thevery end of the Permian significantly changed the morphological and biogeographicalstructure of the Triassic ammonoid communities, which essentially arose anew.178