 The processes responsible for the exceptional preservational quality of the Burgess Shale fossils are far from clear . The interpretation of what is preserved depends partly on two issues that are interlinked : whether the animals were buried where they lived , or washed long distances by sediment flows ; and whether the water at the burial sites was anoxic or provided enough oxygen to sustain animals . The traditional view is that soft bodies and organs could only be preserved in anoxic conditions , otherwise oxygen @-@ breathing bacteria would have made decomposition too rapid for fossilization . This would imply that the sea @-@ floor organisms could not have lived there . However , in 2006 Caron and Jackson concluded that the sea @-@ floor animals were buried where they lived . One of their main reasons was that many fossils represented partially decayed soft @-@ bodied animals such as polychaetes , which had already died shortly before the burial event , and would have been fragmented if they had been transported any significant distance by a storm of swirling sediment . Other evidence for burial where the animals had lived includes the presence of tubes and burrows , and of assemblies of animals preserved while they fed – such as a group of carnivorous priapulids clustered round a freshly moulted arthropod whose new cuticle would not yet have hardened . Fossilized swimming organisms were also buried immediately below where they lived . 
