Systematic relationships of the Mesozoic wood genus Xenoxylon: an integrative biomolecular and palaeobotanical approach

Xenoxylon Gothan is one of the very few components of Mesozoic terrestrial biota which give clear palaeoecological signal. Unfortunately its systematic relationships are still unknown. This work analyzes the organic geochemistry of particularly well preserved samples of Xenoxylon from the Callovian of Łuków (eastern Poland) for comparison with the Bathonian of Gnaszyn (south-central Poland). The wood fragments from both Łuków and Gnaszyn contain phenolic abietanes like ferruginol, 6,7-dehydroferruginol, sugiol, hinokiol or 2-ketototarol. The presence of such biomolecules, with simultaneous absence or very small amount of tetracyclic diterpanes such as phyllocladanes, beyerane and/or kauranes, is characteristic for extant conifer families Cupressaceae s.l. and Podocarpaceae. Thus, the molecular composition of the wood genus Xenoxylon suggests systematic relationships with these extant families. This study presents the evidence that preserved biomarkers and biomolecules are not exceptional in fossil wood, and that their composition generally supports the anatomical data.