Saturday, 3 March 2012

The Rhynie Chert Of Jurassic Argentina

From left to right: top to bottom, the stem of an aquatic
fern,  Equisetum leaf with fungal hyphae within the
structure, Chytrid fungus within a decaying plant stem
The quality of a fossil is very similar to the quality of a photograph. The more pixels in an image, the clearer and more detailed it is. The same can be said for fossils. However it is dependent not upon the number of pixels but on the size of the mineral grains in which it is preserved. The particles in sandstone are visible to the naked eye, creating fossils which show very little bodily detail. A perfect example are the Ediacaran fossils from the Ediacara hills which barely show the outline and large contours of the body.

From left to right, top to bottom: cross section of and
Equisetum stem, cross section of a conifer cone,
longitudinal  section of a conifer cone
Pyrite grains on the other hand are much smaller. The fossils from the Bundenbach Shales in Germany display well preserved internal organs and even their circulatory systems. Sandstone grains and similar are described as being macrocrystalline while grains similar in size to pyrite are described as being microcrystalline. However the very smallest of the small are cryptocrystalline. Minerals such as silica are still difficult to observe even when using an electron microscope with water enhanced magnification.

Cryptocrystalline grains preserve fossils right down the the cellular level and lower, making them the highest quality specimens on Earth. Examples of this come from the Rhynie Chert in north east Scotland. 400 million years ago, the area was covered in a vast peat bog over a series of superheated springs. The boiling water spewing from the bowels of the Earth brought with it silica minerals which were deposited into the bodies of dead creatures, preserving them in perfect detail.

The geothermal wetlands of Yellowstone national 
park are similar to those of Jurassic era Argentina
Now palaeontologists from the National Museum of La Plata and Cardiff University working in Patagonia, Argentina have discovered a second fossiliferous silica deposit near the town of St Agustin. The 150 million year old deposits were laid down during the late Jurassic and preserve, in perfect detail, the remains of a swamp and river system. 'There's a lot more to come. It's a near-intact ecosystem that's beautifully preserved' says Dr. Alan Channing of Cardiff University, a member of the international team analysing the fossils. Apart from a wide variety of crustaceans, plants and insects, the team have discovered several new species, including a plant named Equisetum thermale.

'We have the remains of everything from the bacteria living right around the hot spring vents all the way to the plants, crustaceans and insects living in wetlands further away and the trees and ferns from the forests around the margins......ultimately it's going to be just as important.'