Abstract

Background and Aims Fossil records are indispensable for inferring the phylogeny of the leptosporangiate ferns. Permineralized fossils, which preserve anatomical details, can provide extensive anatomical information necessary for comparison with extant species. Fossil deposits of present-day Antarctica have proven particularly significant for elucidating the evolutionary history of divergence and diversification in the leptosporangiate ferns. In this study, we describe a newly discovered permineralized fossil of Schizaeales from the Cretaceous of Antarctica, with the aim of laying the groundwork for future phylogenetic analyses.Methods The material studied is a permineralized fern reproductive organ preserved in a newly discovered silicified tuffaceous palaeosol from Livingston Island, Antarctica. The fossil-bearing horizon was inferred to correspond to the Williams Point Beds, dated to the mid-Cretaceous (Albian-Cenomanian). Serial sections were prepared using the peel technique, and a three-dimensional reconstruction of the entire organ was generated from the resulting image series using specialized software. In addition, high-resolution images of the remaining specimen were obtained using a newly developed method for ultrafine sequential surface imaging of fossils. Other biota components co-occurring with the target specimen in the matrix were studied using both peel sections and petrographic thin sections for anatomical and taxonomic studies.Key Results The new fossil was designated as a new fossil taxon belonging to the order Schizaeales (family Schizaeaceae s.l.), and is described here as a new permineralized fern reproductive organ: Escuderia livingstonensis gen. et sp. nov. In situ spores were identified as a dispersed spore genus Ischyosporites, allowing the identification of one of the parent plants of that sporomorph. The new fern exhibits peculiar sympodial branching, which is unusual in both extant and fossil Schizaeales. The fossil-containing rock also preserved a gymnosperm ovulate organ of uncertain affinities, conifer shoots and woody root organs, and globose mycorrhizal nodules emerging from the conifer roots, representing part of the biota that coexisted with the fossil fern.Conclusions The new genus Escuderia differs from both extant taxa and previously known fossil forms, exhibiting a primitive branching pattern and other anatomical features that provide new evidence for reconstructing the evolutionary history of the Schizaeales. The finding strengthens the hypothesis that Antarctica may have played a significant role in the diversification of the Schizaeales as well as of other leptosporangiate ferns. This study serves as a starting point for future comprehensive phylogenetic analyses of the Schizaeales, including undescribed permineralized fossils recently discovered in Japan and southern South America.