The first record of the dipterid fern leaf Clathropteris Brongniart from Antarctica and its relation to Polyphacelus stormensis Yao, Taylor et Taylor nov. emend.

We here present newly discovered dipterid fern fossils from the Lower Jurassic of the Transantarctic Mountains. Impression/compression specimens can be assigned to Clathropteris meniscoides Brongniart. This is the first record of C. meniscoides from the Southern Hemisphere and one of only very few Gondwana occurrences of Clathropteris. In addition, newly discovered material of Polyphacelus stormensis Yao, Taylor et Taylor, an anatomically preserved dipterid fern, provides compelling evidence that it represents permineralizations of C. meniscoides. New fertile material of Polyphacelus enables an emendation of genus and species diagnosis to include additional details, i.e., a quadriseriate sporangial stalk, a continuous annulus span and vertical to slightly oblique orientation of the annulus, and trilete spores. As in several other anatomically preserved fossil dipterid ferns, the combination of fertile characters appears intermediate between those of the extant genera Dipteris Reinwardt and Cheiropleuria Presl. The Antarctic fern Clathropteris/Polyphacelus grew under very unstable environmental conditions with high volcanic activity. Sedimentological data and co-occurring plant fossils suggest that this dipterid usually formed part of the herbaceous understorey in an open, bennettitalean-dominated vegetation, but became locally dominant in pioneering communities that colonized freshly exposed habitats, e.g., after catastrophic volcanic events. It is generally assumed that fossil dipterid ferns grew in subtropical to tropical climatic regimes similar to their extant relatives. However, palaeoclimatic reconstructions indicate that the East Antarctic dipterid ferns apparently flourished in a cool-temperate biome in the continental interior of southern Gondwana.