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3800万至3400万年前嵌入树脂中的动物和植物的三维精美保存化石的著名来源。这些内含物中只有一小部分是种子植物，然而，这对于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，对波罗的海琥珀中种子植物内含物的研究主要集中在19世纪和世纪早期，表明琥珀植物群具有多样性。然而，除了针叶树和壳斗科之外，这些历史出版物中描述的大多数标本从未经过全面审查或更新。因此，目前还不清楚，被子植物类群中生长的生物曝气生物滤池。这阻碍了全面的古环境评价的BAF，也有助于其植被对比的看法。目前关于BAF有四种主要假设，即它是一个热带低地森林与亚热带山区（1）;一个亚热带到暖温带山地森林（2）;一个阔叶，潮湿和喜热的森林在平原地形（3）;或一个异质镶嵌的各种生境类型的暖温带和潮湿的气候（4）。在这个项目中，我们的目标是评估这些假设，通过研究被子植物内含物从历史琥珀收藏，以及新的未描述的材料。我们将调查这些夹杂物，使用microCT和同步辐射X射线断层扫描。这将使我们能够访问内含物的内部关键特征，这对于将其识别到家族或属级水平至关重要。为了重建BAF及其栖息地，我们将通过文献研究，主要集中在欧洲的古第三纪和新近纪，收集已发现的植物化石分类群的古生态信息。我们还将进行植物功能类型（PFT）方法，以确定植被的生态组。在古气候分析中，我们将应用共存方法（CA）定量重建波罗的海琥珀植物群的古气候。对于CA，我们将为每个化石分类群确定最近的活体亲属（NLR），并将收集现代气候参数以及NLR的地理分布。计算所有NLR的气候值的重叠，以估计七个气候参数，如年平均温度和降水量。作为最后一步，我们将综合所有结果，从古生态和古气候分析的BAF的一个修订的整体重建，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.