Megaspores from the Lower Jurassic (Pliensbachian) Rotzo Formation (Monti Lessini, northern Italy) and their palaeoenvironmental implications

Mirco Neri,Evelyn Kustatscher,Guido Roghi

doi:10.1007/s12549-017-0314-z

Abstract

The Rotzo Formation is famous for its Lower Jurassic terrestrial flora and marine (invertebrate) and terrestrial (dinosaur footprint) fauna. However, lycophyte macrofossils were never described from this time period in Italy, although palynological analyses yielded abundant lycophyte spores. Dispersed megaspores, in association with charcoal and amber drops, were recently collected from several horizons and outcrops of the Monte Lessini area. Sedimentological and palaeontological data reconstruct the palaeoenvironment as a paralic swamp under a warm and humid (monsoonal) climate. This is the first record of Jurassic megaspores from Italy, increasing our understanding of Jurassic lycophyte diversity, since at least five microspore and five megaspore genera with selaginellalean botanical affinities can be distinguished. Moreover, this underlines how well these brackish environments were adapted for the preservation of fossil plant remains (including amber).

Highlights

The most famous Early Jurassic (Pliensbachian) flora of Italy comes from the Rotzo Formation (Grey Limestone Group), a thick succession of shallow-water carbonates cropping out in the western Veneto and Trentino regions
De Zigno described in his ‘Flora fossilis formationis oolithicae’ (De Zigno 1856– 1868, 1873–1885) 326 species, 82 of which were described for the first time
The Jurassic of Europe is greatly under-represented in terms of both number of recorded species and publications on Mesozoic megaspores compared to Triassic and Cretaceous sediments (e.g. Collinson et al 1985; Kovach and Batten 1989)

Summary

Introduction

The most famous Early Jurassic (Pliensbachian) flora of Italy comes from the Rotzo Formation (Grey Limestone Group), a thick succession of shallow-water carbonates cropping out in the western Veneto and Trentino regions (eastern Southern Alps). The third and last volume (conifers), was never published due to his death in 1892 (for more details see Grandori 1913a, b, 1915; Wesley 1956). A revision carried out by Wesley (1956, 1958, 1966, 1973, 1974) reduced the number of species to 67 including sphenophytes (e.g. Phyllotheca), ferns (e.g. Gleichenites, Dictyophyllum, Coniopteris, Phlebopteris, Matonidium), seed ferns (Sagenopteris, Pseudosagenopteris, Cycadopteris, Dichopteris), cycadophytes (e.g. Sphenozamites, Otozamites, Ptilophyllum, Weltrichia) and conifers (e.g. Brachyphyllum, Pagiophyllum, Elatocladus). Ginkgophytes and lycophytes, two groups well known from Jurassic floras, were, never described from this flora

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