Burgess Shale Type Deposits

Fossils (remains of ancient life or the activities of ancient life) are often common in sedimentary rock layers such as sandstone, shale, and limestone.  Generally, fossilized animal remains in such rocks consist only of the hard, mineralized parts of their bodies.  Examples include the bones of dinosaurs, the shells of clams, and the exoskeletons of trilobites.  Typically, non-mineralized parts such skin, muscles, and other soft tissues are not fossilized.

Very rarely, however, such soft-parts are preserved under special processes of fossilization (see the example of the fossilized jellyfish at the bottom).  Fossil deposits that show such exceptional preservation are very important to paleontologists because they can reveal fossils of entire groups of completely soft-bodied ancient animals, such as worms, that would typically stand next to no chance of entering the fossil record.

Perhaps the most famous "soft-body" deposit is the Burgess Shale of British Columbia, Canada, which was popularized by paleontologist Stephen Jay Gould in his book, Wonderful Life.  The Burgess Shale, a rock layer deposited on the ocean floor, is important--not only because of how well the fossils are preserved--but also because it records a critical interval of the early evolutionary history of animal life: the Cambrian radiation.  While early animals almost certainly evolved before the Cambrian period (which began about 541 million years ago), they did not diversify into the major groupings of animals that we know today until the Cambrian period.  Within the Burgess Shale, one finds fossilized examples of many soft-bodied forms that share some similarities with modern groups of ocean life, but also have many differences.  These similarities and differences are of great interest to paleontologists because they provide us with critical information about early animal evolution. Examples of Burgess Shale fossils.

The Burgess Shale is not the sole record we have of a Cambrian soft-body deposit.  In fact, there are over 50 individual Cambrian localities (see map below) known from around the world that show soft-body preservation, and more likely are waiting to be discovered.

Many of these show preservation similar to that of the Burgess Shale and are therefore said to have "Burgess Shale type preservation." For example, one of the most actively studied Cambrian soft bodied deposits occurs in the Chengjiang region of China.