Burgess Shale is a 508 million-year old fossil deposit in the Rocky Mountains of British Columbia , Canada. Shale is a fine-grained sedimentary rock that is formed by the compression of muds. The Burgess Shale deposit is famous for the abundance and variety of soft-bodied animals preserved as fossils. Such animals tend to decay quickly after death and are rarely preserved. The Burgess Shale has helped paleontologists (scientists who study prehistoric life) better understand the diversity of life that existed during the Cambrian Period . The Cambrian Period marks the start of the Paleozoic Era , a time when animals first became common in the fossil record.
The original Burgess Shale site, named after nearby Mount Burgess and Burgess Pass, was discovered in 1909 by Charles D. Walcott, a paleontologist from the Smithsonian Institution in Washington, D.C. Many kinds of animals discovered by Walcott at that time had never been seen before. These include many strange animals, such as Opabinia, an early arthropod that had five eyes and a long, clawed nozzle above its mouth, and Hallucigenia, a wormlike animal with a series of spines along the length of its body. These animals are now thought to be related to arthropods and some kinds of worms alive today.
During the Cambrian Period, the region that became the Burgess Shale was near the equator. Burgess Shale animals lived on the ocean floor near an underwater cliff called the Cathedral Escarpment. Scientists believe most animals were preserved so finely because they were buried catastrophically by a series of mud flow deposits not far from where the animals lived. Most of the fossils became compressed flat by successive layers of mud and transformed into fossils. The fine mud allowed excellent preservation of the anatomical detail. This allows paleontologists to better understand how these animals might be related to one another and to modern animals, as well as their ecology and mode of life.
A number of different animals first evolved (developed over time) skeletal elements, like shells, during the Cambrian Period. Many of these animals, such as trilobites , are also preserved in the Burgess Shale but often with their soft and delicate limbs in place. In addition, the Burgess Shale preserves some of the earliest members of many animal groups still alive today. For example, fossils of the primitive fish Metaspriggina represent some of the earliest vertebrates (animals with backbones) in the fossil record.
