 Fossil tracks are rare and no burrows under the sea @-@ floor have so far been found in the Burgess Shale . These absences have been used to support the idea that the water near the sea @-@ floor was anoxic . However it is possible that the water just above the sea @-@ floor was oxygenated while the water in the sediment below it was anoxic , and also possible that there simply were no deep @-@ burrowing animals in the Burgess Shale . Some fossils , such as Marrella , are almost always the right way up , which suggests they were not transported far if at all . Others , such as Wiwaxia , are often at odd angles , and some fossils of animals with shelly or toughened components very rarely contain remains of soft tissues . This suggests that the distances over which corpses were transported may have varied between genera , although most were buried where they had lived . 
