Sphenopterid diversity in the Kungurian of Tregiovo (Trento, NE-Italy)

Abstract

The lower Permian fossiliferous deposit of Tregiovo, in the upper Val di Non (Trento Province, N-Italy), is known from the beginning of last century, since it has yielded invertebrate and vertebrate footprints, palynomorphs, conchostracans, and especially plant remains. In recent years, a new section in the Tregiovo Formation, called “Le Fraine”, located along the Lauregno provincial road, has been discovered. Two fossiliferous layers in this new section, one in the lower and one in the upper part of the section, yielded different plant assemblages. The radiometric dating of the volcanic formations under- and overlying the Tregiovo Formation, indicates a middle Kungurian age for the fossil-bearing sequence. More than 1000 specimens, impressions and compressions but without cuticles, have been found. The two plant assemblages are rich and diverse, and both are dominated by conifers (e.g., Feysia, Hermitia, Dolomitia) that range from 60 to 80% of the total assemblage, but also sphenophytes (Annularia), taeniopterids (Taeniopteris) and ginkgophytes (Sphenobaiera) occur. Most remarkable of these two assemblages is the high diversity of sphenopterids that are sometimes preserved as complete fronds. At least five different species can be attributed to the genus Sphenopteris, i.e. Sphenopteris kukukiana, Sphenopteris suessii, Sphenopteris. sp. cf. S. geinitzii, Sphenopteris sp. and a morphotype that represents a new species, Sphenopteris valentinii. The leaves of most Sphenopteris species look pretty stiff and have strongly dissected pinnules with very narrow, linear rigid segments, apparently being an adaptation to arid conditions. The Tregiovo flora is of great importance, not only because of its richness and diversity, especially with regard to sphenopterids, but also because it is one of the very few well-dated Kungurian floras from Euramerica.