Schists of Burgess

The schists of Burgess (named according to the Mont Burgess, located very close to the place where they were found) is a deposit of exposed Schiste black found in the heights of the Rocky Mountains of the Canada in the National park of Yoho close to the town of Fields, in Colombia-British. Fossiles were found there by Charles Doolittle Walcott in 1909. Walcott went back the following years there to collect additional specimens. The majority of the fossils that one finds there, old men of approximately 505 million years, are single with the site, though some trilobites common mid- Cambrien was also found there. These fossils were of a substantial interest because they comprised appendices and soft parts very seldom preserved.

History and significance

It is into 1909 that the paleontologist Charles Doolittle Walcott discovered a layer of Schiste embedded in a wall of the Rocky Mountains in the Yoho National Park on the Western slope of the Mont Stephen in Canada. This mountain was formerly a sea-bed. Sediments of North America seem to be deposited in deep water in the form of flow mud capturing the animals. The scarcity of oxygen with idle their decomposition and they became black and thread-like fossils.

The schist is a type of sedimentary rock made of particles of clay and silt. Many schists are very friable what makes it possible the fossils to appear on the surface.

The body of the animals of Burgess buried in mud, took varied orientations. Mud infiltrated in the bodies and thanks to fine layers of sediment, they separated from the body in various microphone-levels. Thus a certain tridimendionnelle structure was preserved, even during strong compressions of muds. More than 65.000 specimens of more than 120 species were studied.

The significance of the discoveries made in this place was not carried out immediately. Only a reverification of the fossils made in the years 1980 by Harry Whittington, Derek Briggs and Simon Conway Morris of the Université of Cambridge revealed that fauna thus presented was of much richer and complex that what the former paleontologists had not imagined. Indeed, several of the animals present had strange forms and/or odd anatomical elements and only of the minor resemblances to other known forms of life. For example, one finds the Opabinia in five eyes and a horn like a vacuum cleaner; the Aysheaia which resembles extraordinarily a modern Embranchement, the Onychophora; the Nectocaris, which is a shellfish with fins or a Vertébré with carapace and finally, the Hallucigenia, which was originally depicts like going on bilaterally symmetrical spines. Conway-Morris now describes it like another Onychophora with backbones. Other badly interpreted fossils were assembled to form the remainders of a large predator, the Anomalocaris. More recent studies going back from end of the year 1990 to Briggs and Richard Fortey arranges several fossils with the odd forms among the arthropods, but several animals as the Amiskwia remain enigmatic.

The great diversity and the exoticism of the shapes of the fauna of Burgess created a whole controversy in the world of the Paléontologie because of the reasons and the nature of a phenomenon which was going to be called the Explosion cambrienne.

More thorough studies showed that the schists of Burgess extend on many kilometers in the form of " îlots" isolated and various faunas are preserved in multiple places. The deposits seem to be those small pieces of muddy oceanic funds which, time with other, slip along a cliff, carrying with them their faunas and anything else which has misfortune to swim by there in them with low content of Oxygène in the Abysses. Six distinct faunal zones were identified in the schists of Burgess. The scientists knowing what now to seek, of the similar deposits were identified elsewhere, with a similar fauna. Most important of these similar deposits are deposits of floods turbides, even older, created in a way similar to the schists of Burgess in the province of Yunnan in China. These Schistes of Maotianshan contains a fauna extremely similar to that of Burgess.

Being given its localization in the National park of Yoho, the schist is partly a site of the World heritage of UNESCO. Subsequent explorations updated schist exposures on a face of a few dozen kilometers and identified at least six fossiliferous layers in the formation.

List species

Species assigned with an always existing group

Arthropod S

Annélide S

  • Burggessochaeta :

Brachiopod S

Important variety of invertebrates. They developed a hard shell with 2 valves in order to protect their soft part. Installed on sea-beds, they filtered water to retain the edible elements. They are divided into two classes: the inarticulate ones and articulated.

  • Microdictyo

Chordé S

Mollusc S

  • Hyalithes
  • Halkiera

Echinodermatous S

  • Gogia

  • Helicoplacus
  • Eldonia
  • Echmatocrinus

Spongiaires

Cténophore S

Priapulidae

Cnidaire S

Species assigned with an extinct group

Arthropod S

Species whose classification is dubious

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