SPECIES DIVERSITY OF GENUS <i>DUMORTIERIA</i> (GRAPHOCERATIDAE, AMMONOIDEA) IN THE UPPER TOARCIAN DEPOSITS OF THE GREATER CAUCASUS BASIN
The ammonite genus Dumortieria is widely distributed in the Upper Toarcian deposits (Lower Jurassic) of the sedimentary basin of the Greater Caucasus. Revision of the earlier collected data permits to evaluate its species diversity as 17 taxa (exigua, explanata, falcofila, radians, latescens, levesquei, moorei, munieri, pseudoradiosa, radiosa, rhodanica, signata, prisca, striatulocostata, subundulata, suevica, tabulata). Diversity and species composition of Dumortieria from the Greater Caucasus are similar to those of Western Europe, which suggests wide palaeobiogeographical connections of these regions at the end of the Early Jurassic. These connections can be explained by coincidence of the global sea-level rise with the transgression of the Caucasian Sea.