Reproductive diversity of Antarctic glossopterid seed-ferns

Abstract

Glossopterid reproductive structures, both impressions and permineralizations, have been known from Antarctica for decades, but little detailed work has been done on them to date. Impression fossils from the Central Transantarctic Mountains reveal that at least four genera of reproductive organs are present on the continent. Plumsteadia is a genus of multiovulate megasporophylls found on all Gondwanan continents and distinguished by tightly compacted ovules surrounded by a wing which contains a row of ovules at its base. Numerous specimens of Plumsteadia ovata Kyle add additional information on anastomosing venation in the sporophyll and a fluted margin on the wing to the species description. A new species of Rigbya, an ovulate organ, is characterized by the laminar appearance of the cupules/scales and a crenate margin at the apex of the cupules. Eretmonia singulia sp. nov., a microsporangiate structure, is distinguished by the terminal attachment of a single sporangium on a dichotomizing stalk rather than a whorl of sporangia as found in other species. Finally, Arberiella inflectada sp. nov., a cluster of pollen sacs, includes microsporangia with a distinctive, recurved base. These genera are found across Gondwana, suggesting that Antarctica, with its central location in the supercontinent, was a bridge for the distribution of glossopterid genera from one Gondwanan continent to another. A comparison of these new Antarctic taxa to species found on other Gondwana continents is provided to illustrate the diversity and geographic range of glossopterid reproductive structures. The relative scarcity of information garnered from these impression specimens presents a conservative estimate of the diversity of the glossopterid clade, but information from Antarctica adds considerably to our knowledge of this group.