The Burgess Shale
The Burgess Shale is a Canadian rock formation dating from the Cambrian period, the earliest of the great fossil eras. At that time, there were four continents instead of seven, and there were no plants or animals on land. However, the seas were teeming with life and, in an underwater mud bank off the coast of Canada (then just south of the equator), a complex ecological community was flourishing.
Suddenly, 505 million years ago, there was an enormous mudslide that smothered everything in its path and preserved the remains of those animals and plants as fossils. Successive mudslides added layer upon layer of sediment and even more ancient creatures to create what is now the fossil layers of the Burgess Shale.
Over the millions of years since its formation, tectonic forces thrust the Burgess Shale two miles into the air to become part of the Canadian Rockies. Although the fossils were discovered in 1909 by Charles D. Walcott, it was only in the 1970s, that their significance was recognized
The Burgess Shale is considered unusual because it preserves not only organisms with hard skeletons but also soft body tissues and even some internal organs. The creatures captured within it lived during a period in Earth history when a burst of evolutionary activity generated a sudden increase in the complexity and variety of animal life. This "Cambrian Explosion," occurring 540 to 490 million years ago, saw the first appearances of familiar prehistoric animals such as trilobites, as well as many bizarre forms with no known descendants. These include the Wiwaxia, which has been likened to an armored slug with two rows of spikes along its back; the Hallucigenia, which had long-clawed walking tentacles and spiky armor; the Anomalocaris, which was over a meter long and the largest predator of its time; and even a very early ancestor of vertebrates.