Burgess shale

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The Burgess Shale is a black shale found high up in the Canadian Rockies near the town of Field, British Columbia. Fossils were found in the Burgess Shale by C. D. Walcott in 1909. Walcott returned in the following years to collect additional specimens. The majority of the fossils collected were unique to the site although some common Middle Cambrian trilobites were also found. The fossils were of substantial interest because they included appendages and soft parts that are rarely preserved.

A reinvestigation of the fossils in the 1980s by Henry Wittington, Derek Briggs, and Simon Conway-Morris of the University of Cambridge revealed that the fauna represented was much more diverse and unusual than Walcott had recognized. Indeed, many of the animals present had bizarre anatomical features and only the sketchiest resemblence to other known animals. Examples include Opabinia with five eyes and a snout like a vacuum cleaner; Aysheaia which bears an extrordinary resemblance to a minor modern Phylum -- the Onychophora; Nectocaris which is apparently either a crustacean with fins or a vertebrate with a shell; and Hallucigenia which pretty much defied rational description (though it was later proven an onychophoran).

The diversity and exotic nature of the Burgess fauna has caused a great deal of controversy in paleontology with regard to the reasons for and nature of what has come to be called the Cambrian Explosion.

Further investigations showed that the Burgess Shale extends for many miles in isolated outcrops and the various faunas are preserved in different places. The deposits appear to represent small areas of muddy ocean bottom that -- from time to time -- slid down the face of a limestone cliff carrying their fauna and anything unfortunate enough to be swimming by into oxygen-poor waters in the depths. Now that scientists know what to look for, similar deposits have been identified elsewhere with similar faunas. The most important similar deposits are even older turbide flow deposits created in much the same way as the Burgess shales in Yunnan Province, China. These Maotianshan shales contain fauna quite similar to the Burgess.

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