Cambrian Substrate Revolution - Burrowing Before The Cambrian

Burrowing Before The Cambrian

The traces of organisms moving on and directly underneath the microbial mats that covered the Ediacaran sea floor are preserved from the Ediacaran period, about 565 million years ago. The only Ediacaran burrows are horizontal, on or just below the surface, and were made by animals which fed above the surface, but burrowed to hide from predators. If these burrows are biogenic (made by organisms) they imply the presence of motile organisms with heads, which would probably have been bilaterans (bilaterally symmetrical animals). Putative "burrows" dating as far back as 1,100 million years may have been made by animals that fed on the undersides of microbial mats, which would have shielded them from a chemically unpleasant ocean; however, their uneven width and tapering ends make it difficult to believe that they were made by living organisms, and the original author has suggested that the menisci of burst bubbles are more likely to have created the marks he observed. The Ediacaran burrows found so far imply simple behaviour, and the complex, efficient feeding traces common from the start of the Cambrian are absent.

Some simple pre-Cambrian horizontal traces could have been produced by large single-celled organisms; equivalent traces are produced by protists today.