oa Preservation and Palaeochemotaxonomy of Aliphatic Biomarkers in the Mesozoic Plant Fossils from the Tetori Group, Japan

Chemotaxonomy of plant-derived biomarkers (e.g. wax alkanes, cyclic terpenoids) is well documented in modern conifers, while those of major Mesozoic groups including ferns and gymnosperms remain underexplored. The paleochemotaxonomic characterization of these groups is expected to enhance our understanding of paleovegetational reconstructions and the classification of morphologically based fossil taxonomy. This study examined aliphatic biomarkers preserved in Mesozoic gymnosperm and fern fossils from the Tetori Group, Japan. Mesozoic gymnosperm fossils of Brachyphyllum sp. (conifer) and Ptilophyllum sp. (Bennettitales) exhibited distinctive biomarker profiles compared to their host rocks. Analyzed Brachyphyllum sp. suggested a potential association with modern Araucariales, as evidenced by the predominance of tetracyclic diterpenoids, including compounds with an extended alkyl side chain. Ptilophyllum sp. showed a terpenoid composition rich in pimarane-type diterpenoids, indicating a phylogenetic relationship between Bennettitales and conifers. In contrast, fern fossils contained scarce amounts of aliphatic biomarkers, showing similar compositions to their host rocks. This suggests that they originally had lower amounts of specific biomarkers or lost these compounds during diagenesis. These findings underscore the importance of analyzing biomarker profiles in ancient plant fossils to understand their phylogeny and paleovegetations.