Conifer diversity in the Kungurian of Europe: Evidence from dwarf-shoot morphology

Abstract

A major global change, the transition from an icehouse to a greenhouse world, took place during the Permian. In the equatorial Euramerican floral realm this resulted in stepwise changes from sub-humid climates in the early Cisuralian to semi-arid/arid climate by the late Cisuralian. During the same time interval we see a change from spore plant-dominated lowland floras, to increasingly drought-tolerant floras dominated by conifers and other seed plants. A recently discovered Kungurian (late Cisuralian) flora from the “Le Fraine” section near the village of Tregiovo (Trento Province, NE-Italy), is characterized by several types of conifers, callipterids, sphenopterids, and sphenopsids. The conifer fossils included both vegetative and reproductive organs. Five different ovuliferous dwarf shoot types were found, ranging from forms with many scales and interspersed sporophylls, that typically resemble late Pennsylvanian and early Permian walchian conifers, to stalked forms with largely fused sterile scales and sporophylls, comparable to early and late Permian voltzian conifers. One of the voltzian-type dwarf shoots belongs to the genus Dolomitia, extending the range of this genus back to the late Cisuralian. Another form strongly resembles those of the voltzian conifer Pseudovoltzia. The other three dwarf shoot types show a wide morphological variation, but cannot be assigned to any known genus due to the imperfect preservation. In western Euramerica, the transition from walchian- to voltzian-conifer-dominated floras took place during the late Cisuralian. This study shows that this change occurred across the entire equatorial Euramerican realm. The well-dated Tregiovo flora is one of the very few late Cisuralian floras of Euramerica. As such, this flora documents an important step in the evolution of Permian terrestrial biotas.