About million years ago, the continent that would become North America straddled the equator. With no terrestrial plants or animals, the land was a barren landscape.
The warm, shallow sea bordering the continent, however, hosted a carbonated reef teeming with a diverse array of organisms, most of which were relatively small bottom-dwellers.
Periodically, the animals would get washed over the reef and deposited at its base, where their bodies accumulated in the muddy sediments.
Today, these creatures are beautifully preserved in the Burgess Shale. Before the divide, the world, or at least the rock record, appears devoid of life except for a smattering of microbes.
This month marks the centennial anniversary of the discovery of the Burgess Shale. Although scientists have been mining the Burgess Shale for bizarre and unique creatures for a century, the fossil site — and especially the fossil collections currently sitting in museum drawers — still have a lot of surprises for scientists. They were, however, crustaceans unlike any he, or any other paleontologist, had ever seen. Took a large number of fine samples to camp.
Collecting was a family affair, as his wife and several of their children joined him. Walcott honored his son Sidney by naming the first formally described fossil from the Burgess Sidneyia inexpectans.
They eventually collected more than 65, specimens, now housed at the Smithsonian. Walcott hoped to write a definitive study on his Burgess fossils. He published his first paper in April and another five over the next decade. He called these preliminary reports, but he never went further. The site remained somewhat in anonymity until the s, when paleontologist Harry Whittington and two paleontology graduate students at Cambridge University in England, Simon Conway Morris and Derek Briggs, began working on the site.
In , Harvard University professor Percy Raymond opened a second quarry. However, paleontologists know that soft-bodied trilobite ancestors roamed the sea floor at that time because these primitive animals left diagnostic tracks in the mud.
Sidneyia fossil with Sidneyia model. The Cambrian Explosion and the Burgess Shale. May 30, , am , Burgess Shale. Cambrian Explosion. Factors driving evolutionary change in the Cambrian.
The Cambrian Explosion is when animals first became capable of developing biomineralized shells and skeletons. Shells and skeletons provided animals with a framework to get larger. Hard body parts and increased size are two factors that improve an organisms chance to be fossilized. Debate still rages as to the cause of the sudden development of skeletons.
Skeleton formation may have been due to changes in ocean and atmosphere chemistry. They represent entire lineages, major branches on the tree of life, left behind by evolution, most likely in one of the mass extinctions that punctuate the natural history of this planet.
Other lineages did survive, including that of the humble Pikaia , which qualifies as at least a collateral ancestor of the vertebrates, including us. And that raises the profound, almost beautiful mystery that Gould saw in the Burgess Shale, the subject of his book Wonderful Life : Why us? If one could somehow turn the clock back to the Cambrian and run the game again, there is no reason to think the outcome would be the same.
These little creatures, entombed in rock for a half-billion years, are a reminder that we are so very lucky to be here. A science writer and author of the book High Rise , Jerry Adler is a frequent contributor to Smithsonian. He wrote about the role of fire in shaping human evolution in our June issue.
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