Aspects of Permian palaeobotany and palynology .17. Conifer extinction in Europe at the Permian-Triassic junction: Morphology, ultrastructure and geographic/stratigraphic distribution of Nuskoisporites dulhuntyi (prepollen of Ortiseia, Walchiaceae)

The genus Ortiseia is the youngest representative of the Walchiaceae, a presently well-defined family of Late Carboniferous/Permian conifers, characterized by zoidogamy. Species of Ortiseia are a prominent component in the xerophilous Late Permian flora of the Southern Alps. These species produced pollen grains corresponding to the palynological species Nuskoisporites dulhuntyi. In order to minimize the risk of correlating similar but not identical dispersed pollen with Ortiseia, controversies and uncertainties as to the morphological organization of N. dulhuntyi are resolved by applying both light-and electron-microscopy (SEM, TEM). An emended diagnosis is presented. Ultrastructural analysis verifies the absence of a distal aperture; a prepollen condition is therefore emphasized. Confirmed occurrences of N. dulhuntyi remain restricted to the Upper Permian of western, central and southern Europe. First-occurrences are not earlier than Wordian times. Last-occurrences approximate the Permian-Triassic boundary and match worldwide evidence of dieback of arboreous vegetation in the terrestrial biosphere. The deduced extinction of Ortiseia exemplifies the effects of the Permian-Triassic biotic crisis on gymnosperm diversity in the European part of the late Palaeozoic Euramerican floral realm.