Sprecher
Beschreibung
Lichens are generally very rare in the fossil record. Baltic and Bitterfeld ambers are notable exceptions, with hundreds of specimens discovered to date. The fact that the tree resin preserved lichens and associated organisms lifelike in their microhabitats provides reliable insights into structure and composition of Paleogene lichen communities and their interactions with other organisms. The associations include a wide range of growth forms, and the thallus morphologies are in line with a relatively humid and most likely temperate climate of the amber source forests. Symbiotic propagules such as isidia or soredia occur in many amber-preserved taxa, showing that concurrent dispersal of mycobiont and photobiont has a long and successful evolutionary history. Survey of exceptionally large amber specimens with enclosed corticolous communities revealed that crustose lichens were ubiquitous. Although crustose thalli are not readily identifiable in most cases, we confirmed their presence based on well-preserved apothecia, isidia, and frequently associated lichenicolous fungi. Contrarily, competitive large foliose lichens are rare which allowed a number of small delicate foliose and fruticose lichen taxa to share these habitats. Lichens possessing cushion-like spongiostrata on the lower surface of the thallus were very abundant in the European Paleogene amber forests. Such taxa are absent from continental Europe today, pointing to substantial change in the composition of lichen communities within the past 35 million years. Evidence of grazing damage is rare in the fossils, and actualistic experiments pointed to molluscs and mites as grazers of Paleogene foliose lichens.