A Paleogene leaf flora (Profen, Sachsen-Anhalt, Germany) and its potentials for palaeoecological and palaeoclimate reconstructions

Abstract

Leaves as main locations of photosynthesis show various adaptations of morphological and anatomical traits to habitat conditions. By implication, leaf traits of fossil dicotyledonous plants can be used as proxies for reconstructions of palaeoenvironmental and palaeoclimatic conditions. Herein, a Paleogene leaf flora, the Profen-Süd LC assemblage from central Germany, is introduced and its leaf traits are outlined. Based on a preliminary phytosociological analysis, a floristic evaluation with respect to modern comparative vegetation refers to azonal communities predominated by a Rhodomyrtophyllum-Steinhauera riparian association. It mirrors local rather but species-divers vegetation. Morphological (shape; margin; venation) and morphometrical (area; leaf mass per area) leaf parameters are determined on a representative subsample and applied to the Trait Combination Type (TCT) analysis for gross-morphological characterization of fossil leaf assemblages, and to quantitative methods for estimation of palaeoclimate parameters: Climate Leaf Analysis Multivariate Program, Coexistence Approach and Leaf Margin Analysis. As a result the assemblage contains only four out of 16 TCTs. Morphological diversity is assumed to be characteristically low as the TCT pattern is not fundamentally distinct from that of the coeval hinterland flora of Kučlin (Czechia). Leaf size is overwhelmingly microphyll, and leaf mass per area values are in accordance with present-day evergreen forests. Main results refer to a sclerophyllous evergreen broad-leaved forest. All palaeoclimate calculations deliver similar estimates for subtropical climate with frost-free winters and humid conditions but certain seasonality in precipitation. Results are briefly discussed in context to depositional environment and taphonomic aspects. Moreover, traces of insect herbivory on the fossil leaves are treated as additional traits beyond classical parameters. Respective patterns are briefly documented and discussed to obtain deeper insights into ecosystem structure and food webs. Finally, this case study gives rise to several open questions about reliability and meaningfulness of fossil leaf traits and the feasibility in palaeoecological investigations.