Variability of stomatal density and index in the Upper Permian conifer Quadrocladus Mädler-a taphonomical case study

Within an individual needle of this taxon, variations of SD and SI increased almost consistently from the base (100%) to the apex (169%) of the needle (both surfaces). In cuticles of Quadrocladus from fluvial deposits from Culmitzsch (Thuringia, E-Germany), the overall range of both parameters was smaller than in cuticles from marginal marine beds of Frankenberg-Geismar (NW-Hesse, W-Germany). This difference is probably due to the wider variety of (micro-)climatic and edaphic conditions experienced by material from the latter locality. Cuticles from Upper Permian deposits of northern Italy, showed no significant changes in SD, whereas SI showed a significant excursion towards higher values within the investigated profile. Mean values from northern Italy were slightly lower than values from the German deposits, which could be interpreted as an elevated atmospheric pCO2. However, our data suggest that taphonomic distortions (fragmentation of individual needles, mixing of material from different micro-habitats, time averaging) of the data, have to be taken into account when SD and SI of fossil plants, with no closely related living relatives (i.e. same genus or even species), are used as palaeoatmospheric or -climatic proxies, especially when only a small number of cuticles is available for investigation.