The great explosion of diversity

In "Wonderful Life", Stephen Jay Gould gives us a new view on the fossil life forms represented in the Burgess Shale (one of the oldest fossil bearing shale formations on the planet). Previous attempts at examining life forms represented in the record of the shale appear to have suffered from existing category syndrome: trying to shoehorn in anything seen in the shale into the existing categories of life. When H.B. Whittington got around to putting some of the fossils together, he made the astounding discovery that many of the life forms showed body plans that did not cross over the Cambrian extinction boundary that happened after the shale was laid down and that some of these life forms were wholly new to paleontology. Entire phyla (animals of a certain body type) appear to have existed and were then wiped out during the Cambrian extinction event. Many of these phyla are along no body plans known to modern biology. What is striking is the RANDOMNESS of the extinction: there was no underlying similarity between the survivors, those that made it were just lucky. This calls into question the concept of natural selection based on differential survival and speciation. With so many different phyla available, perhaps the different body plans served the purpose that different species (and functioning of those species) served after the extinction event.

Stephen Jay Gould opens up this vista of totally different life forms on our own planet. Strange and exotic to say the least, with many of them lacking in bilateral symmetry. Wonderful life, indeed! However, since the printing of the book, some paleontologists are questioning the classification of so many new phyla on so few representative species and genera. It is possible we may never get the classification thoroughly settled without the help of a time machine. Until then we can just marvel at the possibilities introduced by this book and hope that some larger theory will come along to help link all of these startling life forms into the great branching bush of life.

For those interested in this subject I recommend readings of: Stephen Jay Gould, David Raup, Jack Sepkoski. I am pretty sure that another book or two on the Burgess shale will be in the offing in the next few years, which may shed some more light on the subject of early life on earth.