| dc.description.abstracteng | Amber is fossilized resin that was excreted by conifers or angiosperms. Plant and animal remains which got caught inside of these ancient resin flows are called ‘inclusions’ and are often preserved with high fidelity. Amber deposits which are remarkably rich in inclusions mainly occur in Cretaceous and Cenozoic sediments. The Eocene Baltic amber is a prominent example which constitutes the largest amber deposit worldwide and is famous for its plenitude of inclusions that mainly comprise arthropod taxa.
This thesis, however, focuses on plant inclusions from Baltic amber, which are rare, and less studied than the arthropod inclusions. Despite their rareness, plant inclusions are significant for the reconstruction of the palaeoecosystem from which the amber derives, the so-called ‘Baltic amber forest’. Up to now, knowledge about the ‘Baltic amber forest’ is mainly based on historic descriptions of plant inclusions from the 19th century and on the interpretation of animal inclusions. Contradictory pictures of the ‘Baltic amber forest’ exist, ranging from tropical lowland rainforests with neighbouring subtropical to temperate mountain forests to steppe forests and pure, dense conifer stands that only intermingled with angiosperm trees along their margins. The topography of the Baltic amber source area is mainly interpreted as mountainous, but also theories about a plain landscape exist. Further debates are related to the age of Baltic amber, as well as the locality of its source forests and its botanical origin. These questions were summarized as ‘Baltic amber mysteries’.
The primary focus of this thesis is to achieve a new picture of the ‘Baltic amber forest’ by predominantly using plant inclusions. Amber inclusions from museum and private collections were used to revise described historic specimens and to identify undescribed plant taxa from Baltic amber. Identified plant taxa were then compared to their fossil and extant analogues. This comparison served to reconstruct the potential palaeoecology of plant taxa, as well as their habitat preferences and palaeoclimatic requirements. With this information, plant diversity, habitat types and their structure were reconstructed, thus synthesising a new picture of the ‘Baltic amber forest’.
In this thesis, ten conifer genera were identified from Baltic amber: Calocedrus, Quasisequoia and Taxodium (Cupressaceae), Cupressospermum (Geinitziaceae), Abies, Cathaya, Nothotsuga, Pseudolarix and Pinus (Pinaceae), and Sciadopitys (Sciadopityaceae). The diversity of Cupressaceae is actually higher, since three morphological complexes of Cupressaceous twig fragments and pollen cones were also classified. The majority of all identified conifers has not been verified from Baltic amber before; thus, new candidates for a Baltic amber source plant should be restudied. In addition, newly discovered or revised angiosperm inclusions confirm the presence of Poaceae, Cyperaceae (Rhynchospora), Roridulaceae, Myricaceae (Comptonia), Viscaceae (six species of Arceuthobium), Ericaceae (Cassiope or Calluna), and Fagaceae (quercoid and castaneoid taxa) in the ‘Baltic amber forest’. The named conifers and angiosperms allowed the reconstruction of several habitat types with their respective plant communities from the Baltic amber source area: coastal lowland swamps under brackish-water influence, raised bog habitats, non-brackish inundated back swamps and riparian forests, non-inundated mixed-mesophytic angiosperm-conifer forests with both open habitat patches (such as meadows) and canopy gaps. Moreover, different life forms could be reconstructed, such as parasitic (dwarf mistletoes, Arceuthobium) and carnivorous (Roridulaceae) plants. Previous studies about ferns, bryophytes, liverworts, fungi and lichens from Baltic amber were also considered in the interpretation of the microhabitats of the ‘Baltic amber forest’. They indicated complex and highly diverse communities with epiphytic, terrestrial, saprophytic and parasitic components.
From a palaeobotanical perspective, there is neither evidence of a (sub)tropical ‘Baltic amber forest’, nor of an altitudinal stratification of the source area. This is supported by previous geological studies of the Baltic amber deposit, which suggest a local amber formation and deposition in the Baltic region during the late Eocene. No orogenic events took place in the Baltic region, precluding the presence of mountains in the Baltic amber source area. Comparisons of the Baltic amber flora with fossil assemblages from the central European Palaeogene showed clear differences to (sub)tropical fossil floras. Instead the Baltic amber flora indicates a warm-temperate palaeoclimate with affinities to the extant warm-temperate to temperate floras of East Asia and North America.
The thorough analyses of available plant inclusions from Baltic amber reveal a heterogeneous mosaic-like landscape of the Baltic amber source area in a coastal setting. This heterogeneity allowed the existence of diverse animal and plant taxa with different habitat preferences in close proximity to each other. | de |