Exceptionally preserved fossils provide major insights into the evolutionary
history of life. Microbial activity is thought to play a pivotal role in both the
decay of organisms and the preservation of soft tissue in the fossil record,
though this has been the subject of very little experimental investigation.
To remedy this, we undertook an experimental study of the decay of the
brine shrimp Artemia, examining the roles of autolysis, microbial activity,
oxygen diffusion and reducing conditions. Our findings indicate that
endogenous gut bacteria are the main factor controlling decay. Following
gut wall rupture, but prior to cuticle failure, gut-derived microbes spread
into the body cavity, consuming tissues and forming biofilms capable of
mediating authigenic mineralization, that pseudomorph tissues and structures
such as limbs and the haemocoel. These observations explain patterns
observed in exceptionally preserved fossil arthropods. For example, guts
are preserved relatively frequently, while preservation of other internal anatomy
is rare. They also suggest that gut-derived microbes play a key role in the
preservation of internal anatomy and that differential preservation between
exceptional deposits might be because of factors that control autolysis and
microbial activity. The findings also suggest that the evolution of a through
gut and its bacterial microflora increased the potential for exceptional fossil
preservation in bilaterians, providing one explanation for the extreme rarity
of internal preservation in those animals that lack a through gut.
2015. Vol. 282, 20150476- p.