Reassessment of the chronostratigraphic and paleogeographic distribution of the Permian prepollen genus Nuskoisporites

The genus Nuskoisporites is a common component of Permian palynofloras, with biostratigraphic and paleogeographic importance. Despite the existence of previous revisions of its occurrence, there are still uncertainties concerning its complete stratigraphic range and paleogeographic distribution. This study presents a comprehensive review of historical records, complemented by new morphometric data derived from 446 Nuskoisporites specimens representing ten geographically distinct regions. Three morphometric variables were measured and analyzed using Principal Component Analysis (PCA): total size (diameter), the ratio of total size to central body diameter (P:CB), and the ratio of central body diameter to average laesurae length (CB:L). Two morphotypes can be distinguished based on those characters, each exhibiting different stratigraphic ranges. The older morphotype spans the Pennsylvanian to lower Guadalupian, while the younger form is confined to the upper Cisuralian through Lopingian. Current evidence supports the extinction of Nuskoisporites shortly before or at the Permian–Triassic boundary, thereby reflecting a genuine ecological turnover rather than reworking or preservation bias. Paleogeographic and paleoecological analyses indicate that Nuskoisporites initially had a broad distribution across multiple phytoprovinces and latitudes. However, a marked reduction of its geographic distribution is observed during the Lopingian, restricting the pollen to low-latitude regions of the western Tethys margin, coinciding with intensified global aridification and environmental stress. This integrated approach of Nuskoisporites provides a refined stratigraphic range for the genus and new insights into its ecological dynamics during the end of the Carboniferous and Permian.