EVOLUTIONARY HISTORY OF LATE OLENEKIAN AMMONOIDS IN THE EAST OF THE BOREAL REALM

Abstract

The evolutionary history and phylogenetic relationships of eight Early Triassic ammonoid genera, Xenoceltites, Bajarunia, Nordophiceras, Pseudosvalbardiceras, Boreoceras, Praesibirites, Parasibirites, and Sibirites, are discussed. The patterns and trends of their evolution are proposed. The genera analyzed compose two phylogenetic lineages, which are used as the basis for a biostratigraphic chart of the Upper Olenekian.