Friday, 26 December 2014

New Research Sheds Light On the Preservation Of Soft Tissue

A fossil from the Messel Pit showing soft issue preservation
Bones, shells and teeth: the most common constituents in the fossil record. Their tough phosphate and carbonate minerals offer an excellent chance of preservation lasting millions of years.

Soft tissues, however, are far more delicate. These rarely enter the fossil record, although they can be found in some exceptional locations such as the Burgess Shale, Canada, or the Messel Pits, Germany. A low oxygen environment is thought to play a role in soft tissue preservation, but recently a study of soft-bodied fossils from the Ediacaran period, a time before hard, mineralised body parts evolved, shows that bacteria may also play a vital role in the process.

'The vast majority of the fossil record is composed of bones and shells,' said James Schiffbauer from the College of Arts and Science at MU. 'Fossils of soft-bodied animals like worms and jellyfish, however, provide our only view onto the early evolution of animal life. Most hypotheses as to the preservation of these soft tissues focus on passive processes, where normal decay is halted or impeded in some way, such as by sealing off the sediments where the animal is buried. Our team is instead detailing a scenario where the actual decay helped 'feed' the process turning the organisms into fossils—in this case, the decay of the organisms played an active role in creating fossils.'

550 million year old Conotubus fossils from the Gaojiashan
lagerstatte in China, preserved in three dimensions in pyrite
Schiffbauer and his team conducted a series of chemical analyses on 550 million year old worm tubes known as Conotubus, preserved in pyrite. By determining how the pyrite had formed, the researchers came up with a mechanism to explain the soft tissue preservation.

They suggest that the bacteria within the tubes started breaking down the inhabitants' bodies after death, filling in the cavity with pyrite in the process. 'Normally, the earth is good at cleaning up after itself,' said Schiffbauer. In this case, the bacteria that helped break down these organisms also are responsible for preserving them as fossils.'

Remarkably Schiffbauer's team was able to give a rough time-scale for the pyrite formation - less than 800 years for preservation to take place. The wider context of the discovery is that bacteria which promote pyrite formation, by reducing hydrogen sulphide with iron, may play a major role in soft tissue preservation across the fossil record. If this is the case, it will make the interpretation of fossil evidence easier and more accurate by allowing potential pyrite preservation artefacts to be accounted for.