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

始新世波罗的海琥珀是一个著名的三维来源，保存完好的动物和植物化石，这些化石镶嵌在3800万到3400万年前的树脂中。这些包裹体中只有一小部分是种子植物，但这对了解波罗的海琥珀的来源森林-波罗的海琥珀森林（BAF）非常有价值。到目前为止，对波罗的海琥珀种子植物包裹体的研究主要集中在19世纪和20世纪初，表明琥珀植物群的多样性。然而，除了针叶树和壳斗科外，这些历史出版物中的大多数被描述的标本从未被全面审查或与当前的分类学更新。因此，尚不清楚是哪个被子植物类群生长在BAF中。这阻碍了对BAF进行全面的古环境评价，也导致了对其植被的不同看法。目前关于BAF的假说主要有四种，认为它是热带低地森林和亚热带山地(1)；亚热带到暖温带山地森林(2)；一种在平原上的阔叶、潮湿和喜热的森林；或者是在暖温带和湿润气候中各种栖息地类型的异质马赛克(4)。在这个项目中，我们的目标是通过研究历史琥珀收藏中的被子植物包裹体以及新的未描述物质来评估这些假设。我们将使用微ct和同步加速器x射线断层扫描来研究这些内含物。这将使我们能够访问包含物的内部关键特征，这对于将它们识别为家族或通用级别至关重要。为了重建BAF及其栖息地，我们将通过文献研究收集已发现的化石植物类群的古生态信息，主要集中在欧洲的古近系和新近系。我们还将进行植物功能类型（PFT）方法，以确定植被的生态类群。在古气候分析方面，我们将采用共存法（CA）定量重建波罗的海琥珀区系的古气候。对于CA，我们将为每个化石分类单元确定最近的活亲属（NLR），并将收集现代气候参数以及NLR的地理分布。计算了所有nlr的气候值的重叠，以估计年平均温度和降水等7个气候参数。最后，我们将综合所有古生态和古气候分析的结果，对BAF进行修正的整体重建，并最终评估现有的假设。

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.