Embryos from the Ediacaran Doushantuo Formation are among the most astonishing examples of exceptional fossilization. However, the mechanism of fossilization is
poorly understood, leading directly to debate over the interpretation of the fossils, some
authors even questioning their interpretation as embryos. It has been hypothesized that
microbial processes are responsible for preservation and mineralization of organic tissues.
However, the actions of microbes in preservation of embryos have not been demonstrated
experimentally. We show that bacterial biofilms assemble rapidly in marine embryos,
forming detailed pseudomorphs of cellular organization and structure. We define three
essential steps in embryo preservation: 1) blockage of autolysis by reducing or anaerobic conditions; 2) rapid formation of microbial biofilms that consume the embryo but
form a replica that retains cell organization and morphology; 3) bacterially-catalyzed
mineralization. We identified major bacterial taxa in embryo decay biofilms using
16S rDNA sequencing. Decay processes were similar in different taphonomic conditions,
but bacterial populations depended on specific conditions. Experimental taphonomy
resembles preservation states of fossils. Our data show how fossilization of soft tissues in
sediments is mediated by bacterial replacement and mineralization, providing a foundation
for experimentally creating biofilms from defined microbial species to model fossilization as
a biological process.