Rhynie chert
The Rhynie chert is a Lower Devonian[1] sedimentary deposit exhibiting extraordinary fossil detail or completeness (a Lagerstätte).
The bulk of the Devonian fossil bed consists of primitive plants (which had water-conducting cells and sporangia, but no true leaves), along with arthropods, lichens, algae and fungi.
Second, these cherts are famous for their exceptional state of ultrastructural preservation, with individual cell walls easily visible in polished specimens.
Stomata have been counted and lignin remnants detected in the plant material, and the breathing apparatus of trigonotarbids—of the class Arachnida—(known as book lungs) can be seen in cross-sections.
[6] Trenches were cut into the chert at the end of this period, and Robert Kidston and William Henry Lang worked furiously to describe the plant fossils between 1917 and 1921.
[6] Interest in the chert then waned until the field was reinvigorated by Alexander Geoffrey Lyon in the late 1950s, and new material was collected by further trenching from 1963 to 1971.
[8] The texture of the sinter formed resemble those found today in freshwater streams at Yellowstone which are typically alkaline (pH 8.7) and tepid 20 to 28 °C (68 to 82 °F).
[5] A braided[13] river flowing to the north periodically deposited the sandy layers found in cores when it flooded its banks.
[10] The time between sinter deposition events was too short to allow the populations to develop to climax communities, and correspondingly early colonisers appear most frequently, pseudo-randomly, in logged sequences.
[14] The analysis of rhizomes and rhizoids makes it possible to discern which plants had an active water uptake system (e.g. Horneophyton), and which were likely to have colonised waterlogged surfaces (Asteroxylon).
[16] Analysis of spores shows that the flora was lacking in some elements common elsewhere at this time, likely due to its setting in a mountainous region, rather than in a lowland flood plain like most other fossil deposits.
[19] As a result of its exquisite preservation, the Rhynie chert boasts the most diverse non-marine fauna of its time,[5] and is important for our understanding of arthropod terrestrialisation.
[20] Typical members of the Rhynie chert arthropod fauna include the crustacean Lepidocaris, the euthycarcinoid Heterocrania,[9] the springtail Rhyniella, the possible insect Leverhulmia, the harvestman Eophalangium sheari,[21] Acari (mites), the centipede Crussolum[22] and trigonotarbids in the genus Palaeocharinus.
[25] The largest organism present in Rhynie was probably a fungus, the enigmatic Prototaxites, growing as a mound a metre or more taller than anything in the community, whose isotopic composition varied like a saprotroph and whose septate pores resemble those of fungi.
In the rare instances that cyanobacteria are found in the fossil record, their presence is usually the subject of much controversy, for their simple form is difficult to distinguish from inorganic structures such as bubbles.
[31] The Rhynie chert, by preserving a snapshot of an ecosystem in situ in high fidelity, gives a unique opportunity to observe interactions between species and kingdoms.
[33] In addition, a fossil enoplid nematode named Palaeonema parasitised Aglaophyton plants, with eggs, juveniles and adults all recorded from within their stomatal chambers.
