The Rhynie chert Lagerstätte – An Early Devonian hot-spring ecosystem frozen in time

The Early Devonian Rhynie chert Konservat Lagerstätte in Aberdeenshire, Scotland, contains an abundance of structurally preserved fossils of organisms that lived together in an early terrestrial geothermal-wetland ecosystem, including cyanobacteria, fungi and fungus-like organisms, algae, land plants, and animals ranging from testate amoebae to nematodes and aquatic crustaceans to the earliest harvestmen, which were fully adapted to life on land. The chert also provides ample direct evidence of interactions between different organisms. Many of the fossils are preserved in situ and reveal astonishing details at the (sub-)cellular level, suggesting that entombment in silca has occurred rapidly to virtually instantaneously. However, not all fossils from the Rhynie chert are excellent; there are also signs of desiccation and shrinkage, as well as biological decay and mechanical destruction. Understandably, most attention has been directed at the well-preserved fossils, while the tattered, fragmented, (partially) decayed, and otherwise inferior ones have received little attention. In this article, we present examples of the varying quality of preservation of organic remains in the Rhynie chert and discuss the taphonomic processes that have led to this. We focus on land plant reproductive biology, microbial fossils, and different levels of fungal interaction, three aspects that stand out in the fossil content of the Rhynie chert Lagerstätte.