THE MIDDLE CAMBRIAN Burgess Shale

In the early 1900’s, a sharp-eyed paleontologist named Walcott was doing field work in British Columbia, and he found a Lagerstätte from the Middle Cambrian Burgess Shale Member of the Stephen Formation. 

The Cambrian Period began 541 million years ago. The Burgess Shale is of Middle Cambrian age in the earliest part of the Paleozoic.

A “Lagerstätte” is a German word used to designate any exceptionally well preserved fossil fauna or flora. Walcott and subsequent researchers collected and described more fossils. They stored them in established museums so that other paleontologists could access them for detailed study. Eventually, researchers began to realize that the Burgess Shale Lagerstätte represented soft-bodied animals that existed near the beginning of complex animal life on Earth. The research process took many years, and the findings were, in some cases, quite controversial about the exact type of organism that each different fossil represented. Research continues to the present day. The Burgess Shale fossil area is now a World Heritage Site. The localities are protected and require authorization to visit. Unauthorized collecting is prohibited.

The modes of preservation of the Burgess Shale Lagerstätte are either impressions (as shown above in the example of a an early “velvet worm” type of animal) in brown mudstone, or, more spectacularly, as  paper-thin carbonized (whitish to gray) imprints in very fine-grained black to gray siliceous mudstone. 

One popular interpretation about their burial environment is that the animals lived in shallow-marine waters at the edge of an underwater cliff. They were transported a short distance by currents over the cliff and down into deep-quiet waters, where they were rapidly buried by muds. Like most interpretations, this one was recently challenged, and some workers maintain that the animals actually lived at the bottom of the cliff and were not transported there. 

The next five posts highlight examples of fossils found in the Burgess Shale strata. These examples show some rather strange-looking animals, including (the last of the examples) of possibly the first back-boned animal.