Abstract
Ammonoids Paramexicoceras aldanense Popow were found at the base of the Nekuchan Formation (upper part of the Changhsingian Stage) in the Dyba River basin, South Verkhoyanie. The first discovery of goniatites in the Upper Permian of Northeast Asia made it possible to clarify the biostratigraphic subdivision of the boundary Permian-Triassic deposits. The Otoceras concavum Zone in its lower part is reduced due to the establishment of the Paramexicoceras aldanense Beds at the base of the Nekuchanian Regional Stage. The data obtained indicate that the genus Paramexicoceras, previously considered long-lived, belongs to the youngest and short-lived taxa of the Cyclolobidae, representing the terminal phase of the goniatite development. This record made it possible to compare the base of the Nekuchanian Regional Stage in South Verkhoyanie with the upper part of the Foldvik Creek Group in East Greenland.
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