Everything about The Burgess Shale totally explained
The
Burgess Shale contains a unique and famous fossil bed displaying exceptional preservation (
Konservat-Lagerstätte). It is a
Cambrian black
shale formation in the
Canadian Rockies of
British Columbia,
Canada. It is in
Yoho National Park, near the town of
Field and is named after
Burgess Pass.
The
Burgess Shale fauna have great scientific value because they include
fossilized appendages and soft
organic parts that are rarely preserved in the
fossil record. The fossils were discovered 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 more recent studies demonstrate that many in fact belong to entirely new animal
phyla — and even in the 21st century some of the
invertebrate fossils have proven
impossible to classify.
History and significance
The significance of the finds wasn't 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 hose;
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 large predatory organism 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 fossils. 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) 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.
Canadaspis
Leanchoilia
Marrella
Naraoia (trilobite)
Olenoides (trilobite)
Perspicaris
Sidneyia
Yohoia
Pikaia
Ctenorhabdotus
Fasciculus
Xanioascus
Haplophrentis
Aysheaia
Hallucigenia
Choia
Ottoia
Genera of uncertain classification
Amiskwia
Anomalocaris
Dinomischus
Nectocaris
Odontogriphus
Opabinia
Orthrozanclus
Thaumaptilon (originally thought a type of sea pen, now believed by some an Ediacaran survivor)
WiwaxiaFurther Information
Get more info on 'Burgess Shale'.
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