BURGESS SHALE

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The 'Burgess Shale' is a black shale fossil bed (Konservat-Lagerstätt) named after Burgess Pass, close to where it was found, high up in the Canadian Rockies in Yoho National Park near the town of Field, British Columbia. Fossils were first discovered in the 'Burgess shale' in 1909 by Charles Doolittle Walcott, who returned in the following years to collect additional specimens. Walcott recognized that the arthropod-like macrofossils were new, unique species, but careful reexaminations showed that many in fact constituted entirely new phyla of life -- and even in the 21st century some of the invertebrate fossils have proven impossible to classify. The 'Burgess shale fauna' are especially valuable because they include fossilized appendages and soft organic parts that are all-too-rarely preserved in the fossil record.

Contents

History and significance

Partial species list

Species assigned to a group of extant taxa

Species assigned to a group of extinct taxa

Species of uncertain classification

See also

References

Further reading

Sources

History and significance

The significance of the finds was not realised at the time of discovery; the trilobites found dated the fossils to the Middle Cambrian period, and Charles Walcott simply placed the unusual new species within the phyla known to exist during that period, a process Stephen Jay Gould dubbed "shoehorning" in his book about the Burgess Shale, ''Wonderful Life'' (1989). A reinvestigation of the fossils in the 1980s by Harry Blackmore Whittington, Derek Briggs, and Simon Conway Morris of the University of Cambridge, however, revealed that the fauna represented were much more diverse and unusual than Walcott had recognized. Indeed, many of the animals present had bizarre anatomical features and only the sketchiest resemblance to other known animals. Examples include ''Opabinia'' with five eyes and a snout like a vacuum cleaner; ''Aysheaia'' which bears an extraordinary 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 was originally reconstructed as walking on bilaterally symmetrical spines. Conway Morris now reconstructs it as another onychophoran, with the spines on its back. Several poorly understood fossils were found to be body parts of a predatory form known as ''Anomalocaris''. More recent (late 1990s) work by Derek Briggs and Richard Fortey has placed many of the "peculiar" Burgess Shale fossils within the arthropoda, but many animals such as ''Amiskwia'' remain enigmatic.
Gould's ''Wonderful Life'', published in 1989, popularized the Burgess Shale discovery. Gould suggests that the extraordinary diversity of the fossils indicate that life forms at the time were much more diverse than those that survive today and that many of the unique lineages were evolutionary experiments that became extinct. He suggests that this interpretation supports his hypothesis of evolution by punctuated equilibrium. However the widely accepted reclassification by Derek Briggs and Richard Fortey contradicts this account and both those authors have criticised Gould for what they believe is a hasty and incomplete analysis used to support Gould's own ideas and which has since entered the popular public consciousness.

The diversity and exotic nature of the Burgess fauna (Middle Cambrian, 505 mya^[1]) has caused a great deal of controversy in paleontology with regard to the reasons for and nature of the preceding period in the history of life that 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, turbidite flows by gravity currents, carrying their fauna and anything unfortunate enough to be swimming by into oxygen-poor waters in the depths. Six distinct faunal zones have been identified in the Burgess Shale. 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 turbidite 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.
Due to its location within Yoho National Park, the shale is part of a UNESCO World Heritage Site, specifically, the Canadian Rocky Mountain Parks. Subsequent exploration has found exposures of the shale over a front of several dozen kilometers and has identified at least six fossiliferous lagerstätten within the formation.

Partial species list

Species assigned to a group of extant taxa

★ ''Thaumaptilon'' (a type of sea pen)

★ ''Aysheaia'' (phylum Onychophora)

★ ''Sidneyia'' (arthropod)

★ ''Pikaia'' (phylum Chordata)

★ ''Canadia'' (annelid)

★ ''Choia'' (sponge)

★ ''Ottoia'' (priapulid worm)

★ ''Canadaspis'' (arthropod)

★ ''Perspicaris'' (arthropod)

★ ''Leanchoilia'' (arthropod)

★ ''Yohoia'' (arthropod)

★ ''Hallucigenia'' (phylum Onychophora)

★ ''Ctenorhabdotus'' (Ctenophora)

★ ''Fasciculus'' (Ctenophora)

★ ''Xanioascus'' (Ctenophora)

Species assigned to a group of extinct taxa

★ ''Haplophrentis'' (phylum Hyolitha)

★ ''Marella'' (arthropod)

★ ''Olenoides'' (trilobite)

★ ''Naraoia'' (trilobite)

Species of uncertain classification

★ ''Amiskwia''

★ ''Anomalocaris''

★ ''Dinomischus''

★ ''Nectocaris''

★ ''Odontogriphus''

★ ''Opabinia''

★ ''Orthrozanclus''

★ ''Wiwaxia''

See also

★ Body form

★ Fossil parks -- protected fossiliferous sites world-wide

★ Invertebrate paleontology

★ History of invertebrate paleozoology

★ List of fossil sites ''(with link directory)''

★ List of notable fossils

★ Micropaleontology

★ Paleobiology

★ Paleozoology

★ Treatise on Invertebrate Paleontology (50 volumes; 1953 to 2006, and continuing)

References

1. Age of Burgess Shale

Further reading

★ Simon Conway Morris, ''The Crucible of Creation: The Burgess Shale and the Rise of Animals'', Oxford University Press, Oxford, 1998 (paperback 1999) ISBN 0-19-850197-8 (hbk), ISBN 0-19-286202-2 (pbk)

★ Richard Fortey, ''Trilobite: Eyewitness to Evolution'', Flamingo, 2001. ISBN 0-00-655138-6

★ Stephen Jay Gould, ''Wonderful Life: Burgess Shale and the Nature of History'', Vintage, 2000. ISBN 0-09-927345-4

★ Derek E. G. Briggs, Douglas H. Erwin, & Frederick J. Collier, ''The Fossils of the Burgess Shale'', Smithsonian, 1994. ISBN1-56098-364-7

Sources

★ The Burgess Shale Geoscience Foundation - official web site

★ The Burgess Shale - Evolution's Big Bang - Burke Museum of Natural History and Culture web pages resourcing an exhibition devoted to the Burgess Shale

★ Burgess Shale Fossils

★ The Cambrian Explosion - BBC Radio 4 broadcast, ''In Our Time'', 17 February 2005, hosted by Melvyn Bragg (includes links to resource pages)

★ Stephen Jay Gould (1989), ''Wonderful Life: The Burgess Shale and the Nature of History'' (New York: W. W. Norton). This best-seller critiques Charles Doolittle Walcott's discovery; and it provides over two dozen illustrations of the metazoans found.

★ Paleobiology Database The Burgess Shale (skeletonized fauna), Stephen Fm., British Columbia, Canada: St Davids, British Columbia

★ Paleobiology Database Hanburia gloriosa, Phyllopod Bed, Burgess Shale, Canada - Whittington 1998: St Davids - Merioneth, British Columbia

★ Smithsonian Museum

★ Species index from the Smithsonian Institution