Photo of the Week #2

Ok, it has been more than a week since I last put up a photo of the week post so I apologize for the lateness of this next installment.

Anyways, here it is:

The Burgess Shale

The topic of this weeks post is the nightmare world pictured above. Believe it or not, this is an artists representation of what life 530 million years ago would have looked like in a shallow equatorial sea located in Alberta, Canada at a location now known as the Burgess Shale in Yoho National Park. The Burgess shale represents a rare window into what life was like in the Cambrian period. Part of what makes the Burgess shale so special is the degree of preservation of soft tissue found in the fossil organisms. Most fossils that we find today only preserve the "hard parts" such as shells, bones and exoskeletons because all of the soft body tissues have decayed. However, at the Burgess shale everything is preserved including soft tissues that normally decay quite quickly.  This allows paleontologists to examine organisms that would never have been preserved otherwise and to see details of organisms that would not have been preserved under normal circumstances. Fossil deposits such as the Burgess shale that preserve unusual features or large number of fossils have a special geologic term: lagerstatten, which is the German word for "mother lode".

So what are these abnormal circumstances that have allowed the Burgess Shale to preserve the soft tissues? To answer this question we must examine how the Burgess Shale was formed in the first place. The creatures of the Burgess shale lived on or near a large carbonate reef platform, kind of like a large underwater tower of algae and large sponges that were capable of building reefs similar to the coral reefs of today.

Schematic of the Burgess Shale

However, one unlucky day, a large mudslide occurred transporting the creatures into deep water and burying them under millions of tonnes of mud. Not a pleasant way to die! The wonderful thing about this mudslide is that once the creatures were buried there was not enough oxygen to cause decay. In order for decay to occur oxygen must be present, and in these anoxic conditions the soft tissues were preserved. As you can see below every detail of these creatures is visible.

Here are some pictures of the Burgess shale fossils:

Hallucigenia

Hallucigenia

Marella (this poor guy got squished during the slide) The black mark on the rock behind it are its insides.

Marella

Opabinia

Opabinia

The importance of the Burgess shale is more than just well preserved and attractive fossil specimens. The Burgess shale has preserved over 140 different species of organism, many of which belong to previously unknown phyla and have given us insight into the very beginnings of life in a much more detailed and complete way than was previously known. Furthermore, many of the Burgess shale fauna have descendants that still exist today, which elucidates a family tree extending back to the beginning of complex life.  Alternatively, some of the Burgess shale fauna represent failed experiments in evolution and are dead-ends in the tree of life, which, without such well preserved fossils we would never have dreamt existed. 

For more information on the Burgess shale visit these websites:

The Burgess Shale Geoscience Foundation: http://www.burgess-shale.bc.ca/

The Smithsonian Museum of Natural History: http://paleobiology.si.edu/burgess/

Matt