Significance to Science?

The Significance of the Rhynie Plants

At the end of the Silurian there began a rapid burst of evolution in plants. Within just 25 million years during the Devonian period, recognised as being one of the two intervals of greatest expansion in plant evolution, land plants evolved complex vascular systems, leaves which specialised in photosynthesis, and roots and stems for support. Most significantly sporangia were developed and seed-bearing plants evolved. More over, the biochemical and physiological processes required to support such complex organisms also developed.

The exceptional preservation of the flora in the Rhynie chert provides botanists and palaeobotanists with a unique window of a time early on in this period of rapid evolution, about 400 million years ago, during the Early Devonian. It gives scientists an insight into the morphology and detailed internal anatomy of these early land plants (in fact in some cases cellular preservation is so exquisite, that the anatomy of a number of the Rhynie plants, for example Rhynia gwynne-vaughanii and Aglaophyton major, is better known than many living plant species!). The Rhynie plants also provide clues as to the probable evolutionary pathways that gave rise to modern plants and also the mechanisms by which plants adapted to terrestrial habitats.

The Significance of the Rhynie Prokaryotes

Another reason the Rhynie chert is important to palaeobotanists, botanists, and life and earth scientists in general, is the presence of fossilised bacteria and cyanobacteria, some of which may have been thermophyllic, thriving within hot springs and their outflow channels.

Prokaryotic organisms provide a fascinating glimpse of the beginnings of life on Earth. Many modern mycoplasms (organisms related to bacteria, but of simpler structure and smaller size) are capable of independent existence and are probably very similar to the first living things. Anaerobic bacteria may resemble organisms which lived when free oxygen was not available. Cyanobacteria, being aerobic must have evolved as oxygen began to diffuse into the atmosphere. Once oxygen was available, cyanobacteria would have been responsible for increasing its concentration as a bi-product of photosynthesis.

Certain types of bacteria found in modern hot springs thrive in boiling water, in alkaline and even highly acidic waters, and many cyanobacteria tolerate temperatures up to 73oC. As such, the study of these organisms living in extreme conditions in hydrothermal areas, and their fossilised forms in the Rhynie chert, is not only important in understanding how life evolved on Earth but may also have implications for future studies in the search for life on other planets.

The Late Silurian saw the invasion of terrestrial environments by invertebrates, in particular groups of arthropods , including myriapods (such as millipedes, centipedes and the extinct arthropleurids) and arachnids. A rapid burst of evolution from this time to the end of the Devonian not only saw the expansion of these and other arthropod groups, most notably the development of winged insects, but also, significantly, the evolution of air-breathing vertebrates and their adaptation to terrestrial habitats.

The Early Devonian Rhynie chert was deposited early on in this period of evolution and diversification about 400 million years ago. The exceptional preservation of the Rhynie fauna allows zoologists and palaeontologists to examine these early terrestrial, and freshwater, invertebrates in terms of their anatomy, and to determine how the various arthropod groups evolved and adapted to live in these new habitats. For example how centipedes and arachnids separately developed the means to breath air: centipedes developed an internal network of tubes or trachea; whereas in arachnids (esp. trigonotarbids) the anterior abdominal appendages where developed into filliform book-lungs.

By studying the associated in situ biota in the individual chert beds, much information can also be gathered on the interactions between fauna, flora and the inorganic environment, thus helping to build a picture of early terrestrial and freshwater ecosystems.

As well as the palaeontological and palaeobotanical significance of the Rhynie chert konservat lagerstätte, there are also other aspects of this unique deposit that are important to geologists.

At 400 million years old, the Rhynie chert is the earliest known, unequivocal, metalliferous, siliceous hot spring deposit that preserves surface 'sinters' and evidence of geyser activity. Hot spring deposits, and particularly their surface expressions, are relatively rare in the rock record. As such the Rhynie chert and its associated sedimentary rocks gives geologists one of the few examples of an ancient hot spring complex.

The Rhynie chert is also important to geologists in understanding the processes through which organisms may be included in the fossil record; such as taphonomy (processes affecting organic remains after death and prior to burial), biostratinomy (processes affecting organic remains during deposition and burial) and diagenesis (processes affecting the rocks and their included organic remains after burial). For example, studying this deposit and the preservation of its biota helps in an understanding of the processes of silicification and how silica can preserve organic remains.