Tuesday, November 20, 2007

Nature's Sketchbook

As I mentioned the Burgess Shale fossils in my Desert Island Books selections, I thought I'd just explain the importance of them.

If you ever wanted to find the closest things to aliens on this planet, forget Men in Black and Greys hiding amongst us and look instead to Yoho National Park, high up in the Canadian Rockies. In 1909, a paleontologist called Charles Doolittle Walcott discovered some interesting fossils in a black shale bed that became known as the Burgess Shale (as it is near the Burgess Pass). Over several expeditions, Walcott collected many fossils from the shale which he identified as new species of arthropod.

However, later examination of Walcott’s fossils in the 1980s revealed a startling truth – what Walcott had discovered were not new species but wholly new types of organisms. Work by Harry Whittington, Derek Briggs and Simon Conway Morris showed that many of the Burgess Shale creatures in fact constituted whole new phyla.

A phylum (pl. phyla) is a large family group. The phylum to which we, and most vertebrates, belong is Chordata. This includes all mammals, reptiles and birds. Insects belong to the phylum Arthropoda, which also includes other jointed-legged animals like spiders, scorpions, woodlice, lobsters and crabs. All of the animals on Earth can be classified within some 30-odd phyla; 95% of species within just nine families. Therefore the discovery of any new phylum is an extraordinary find.

The Burgess Shale, and subsequent similar discoveries in the Maotianshan Shale of Yunnan Province in China and other shale sites, of similar species have added at least six new phyla to the story of life. Many of the species still defy classification today.

The creatures of the Burgess Shale lived in the Middle Cambrian Era, around 500 million years ago when there was a sudden ‘explosion’ of diversity in animal types and body-plans. This is sometimes referred to as the Big Bang of Evolution. It was a time when nature experimented with many different designs for life, most of which proved ultimately to be unsuccessful. Among the fossils so beautifully preserved in the finely textured shale were creatures like Opabinia, which had five eyes and a snout like a vacuum cleaner attachment tipped with a grasping claw, the huge (at 3 feet long it was one of the largest animals on the planet at that time) predatory Anomalocaris with its grasping arms and food disposal-type grinding mouth, and the wonderfully named Hallucigenia that walked on tubular feet - each apparently equipped with a mouth - and was armed with huge spikes; scientists are still not entirely sure which end of the animal was the head and which was the tail.
The Burgess Shale is a truly extraordinary window into that moment when all things were possible for life on this planet. The fossil record is Nature's sketchbook of ideas and it's a fascinating thought to consider just what life might have looked like if some of these designs had survived.

Illustration of Hallucigenia by Mary Parrish for The Smithsonian.
Illustrations of Anomalocaris and Opabinia by John Sibbick.

Recommended Reading:

Wonderful Life: Burgess Shale and the Nature of History by Stephen Jay Gould (ISBN 0-09-927345-4)
The Crucible of Creation: The Burgess Shale and the Rise of Animals by Simon Conway Morris (ISBN 0-19-850197-8, ISBN 0-19-286202-2)
Trilobite: Eyewitness to Evolution by Richard Fortey (ISBN 0-00-655138-6)
The Fossils of the Burgess Shale by Derek E. G. Briggs, Douglas H. Erwin, & Frederick J. Collier (ISBN1-56098-364-7)

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