Towards a holistic reconstruction of the ‘Baltic amber forest’ – angiosperm diversity and its palaeoecological implications

• Applicant: Dr. Eva-Maria Sadowski
• Subject Area: Geology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 535296903

Eocene Baltic amber is a well-known source for three-dimensional, exquisitely preserved fossils of animals and plants that were embedded into resin 38 to 34 millions of years ago. Only a small percentage of these inclusions are seed plants, which are, however, very valuable for understanding the source forest of Baltic amber, the Baltic amber forest (BAF). So far, seed plant inclusions from Baltic amber were mainly studied during the 19th and early 20th century, indicating a diverse amber flora. However, with the exceptions of conifers and Fagaceae, most of the described specimens from these historic publications were never comprehensively reviewed or updated with current taxonomy. Hence, it remains unclear, which angiosperm taxa grew in the BAF. This impedes a comprehensive paleo-environmental evaluation of the BAF and also contributes to the contrasting perceptions of its vegetation. There are currently four main hypotheses about the BAF, suggesting that it was a tropical lowland forest with subtropical mountain areas (1); a subtropical to warm-temperate mountainous forest (2); a broad-leaved, humid and thermophilous forest in a plain relief (3); or a heterogeneous mosaic of various habitat types in a warm-temperate and humid climate (4). In this project, we aim to evaluate these hypotheses, by studying angiosperm inclusions from historic amber collections, as well as new undescribed material. We will investigate these inclusions, using microCT and synchrotron X-ray tomography. This will allow us to access internal key features of the inclusions, which are essential to identify them to family or generic level. For reconstructing the BAF and its habitat(s), we will assemble information on the paleo-ecology of the found fossil plant taxa through literature research with main focus on the Paleogene and Neogene of Europe. We will additionally conduct the Plant Functional Type (PFT) approach that allows determining ecological groups of the vegetation. For the paleo-climatic analysis, we will apply a Coexistence Approach (CA) to quantitatively reconstruct the paleo-climate for the Baltic amber flora. For the CA, we will identify the nearest living relative (NLR) for each fossil taxon and will assemble modern climate parameters as well as the geographic distribution of the NLRs. The overlap of climatic values for all NLRs are calculated to estimate seven climatic parameters, such as the mean annual temperature and precipitation. As a final step, we will synthesize all results from the paleo-eocological and paleo-climatic analysis to a revised holistic reconstruction of the BAF and eventually evaluate the existing hypotheses.

• DFG Programme: Research Grants