Burgess Shale

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Burgess Shale
Stratigraphic range:
Miaolingian
~508  Ma
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Ottoia tricuspida ROM 63057.jpg
Ottoia , a soft-bodied worm, abundant in the Burgess Shale. (From Smith et al. 2015)
Type Geological formation
Unit of Stephen Formation
Thickness161 meters (528 ft) [1]
Lithology
Primary Shale
Location
Coordinates 51°26′N116°28′W / 51.433°N 116.467°W / 51.433; -116.467
Region Yoho National Park and Kootenay National Park
Country Canada
Type section
Named for Burgess Pass
Named by Charles Doolittle Walcott, 1911
Canadian Rockies highlighting Yoho National Park.png
Map highlighting Yoho National Park in red

The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. [2] [3] It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years old (middle Cambrian), [4] it is one of the earliest fossil beds containing soft-part imprints.

Contents

The rock unit is a black shale and crops out at a number of localities near the town of Field in Yoho National Park and the Kicking Horse Pass. Another outcrop is in Kootenay National Park 42 km to the south.

History and significance

The first complete Anomalocaris fossil found. ROM-BurgessShale-CompleteAnomalocarisFossil.png
The first complete Anomalocaris fossil found.

The Burgess Shale was discovered by palaeontologist Charles Walcott on 30 August 1909, [5] towards the end of the season's fieldwork. [6] He returned in 1910 with his sons, daughter, and wife, establishing a quarry on the flanks of Fossil Ridge. The significance of soft-bodied preservation, and the range of organisms he recognised as new to science, led him to return to the quarry almost every year until 1924. At that point, aged 74, he had amassed over 65,000 specimens. Describing the fossils was a vast task, pursued by Walcott until his death in 1927. [6] Walcott, led by scientific opinion at the time, attempted to categorise all fossils into living taxa, and as a result, the fossils were regarded as little more than curiosities at the time. It was not until 1962 that a first-hand reinvestigation of the fossils was attempted, by Alberto Simonetta. This led scientists to recognise that Walcott had barely scratched the surface of information available in the Burgess Shale, and also made it clear that the organisms did not fit comfortably into modern groups.

Excavations were resumed at the Walcott Quarry by the Geological Survey of Canada under the persuasion of trilobite expert Harry Blackmore Whittington, and a new quarry, the Raymond, was established about 20 metres higher up Fossil Ridge. [6] Whittington, with the help of research students Derek Briggs and Simon Conway Morris of the University of Cambridge, began a thorough reassessment of the Burgess Shale, and revealed that the fauna represented were much more diverse and unusual than Walcott had recognized. [6] Many of the animals present had bizarre anatomical features and only the slightest resemblance to other known animals. Examples include Opabinia , with five eyes and a snout like a vacuum cleaner hose and Hallucigenia , which was originally reconstructed upside down, walking on bilaterally symmetrical spines.

With Parks Canada and UNESCO recognising the significance of the Burgess Shale, collecting fossils became politically more difficult from the mid-1970s.[ clarification needed ] Collections continued to be made by the Royal Ontario Museum. The curator of invertebrate palaeontology, Desmond Collins, identified a number of additional outcrops, stratigraphically both higher and lower than the original Walcott quarry. [6] These localities continue to yield new organisms faster than they can be studied.

Stephen Jay Gould's book Wonderful Life , published in 1989, brought the Burgess Shale fossils to the public's attention. Gould suggests that the extraordinary diversity of the fossils indicates that life forms at the time were much more disparate in body form than those that survive today, and that many of the unique lineages were evolutionary experiments that became extinct. Gould's interpretation of the diversity of Cambrian fauna relied heavily on Simon Conway Morris's reinterpretation of Charles Walcott's original publications. However, Conway Morris strongly disagreed with Gould's conclusions, arguing that almost all the Cambrian fauna could be classified into modern day phyla. [7]

The Burgess Shale has attracted the interest of paleoclimatologists who want to study and predict long-term future changes in Earth's climate. According to Peter Ward and Donald Brownlee in the 2003 book The Life and Death of Planet Earth , [8] climatologists study the fossil records in the Burgess Shale to understand the climate of the Cambrian explosion. It can be used to predict what Earth's climate would look like 500 million years in the future as a warming and expanding Sun, combined with declining CO2 and oxygen levels, eventually heat the Earth toward temperatures not seen since the Archean Eon 3 billion years ago (before the first plants and animals appeared). This in turn furthers understanding of how and when the last living things on Earth could potentially die out. See also Future of the Earth.

After the Burgess Shale site was registered as a World Heritage Site in 1980, it was included in the Canadian Rocky Mountain Parks WHS designation in 1984.

In 2012, the discovery was announced of another Burgess Shale outcrop in Kootenay National Park to the south. In just 15 days of field collecting in 2013, 50 animal species were unearthed at the new site. [9]

IUGS geological heritage site

In respect of the site being 'characterized by exceptional soft-tissue preservation, [and containing] the most complete fossil record of Cambrian (Wuliuan) marine ecosystems', the International Union of Geological Sciences (IUGS) included the 'Burgess Shale Cambrian Paleontological Record' in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an 'IUGS Geological Heritage Site' as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.' [10]

Geological setting

Satellite image of the area. Burgess Shale, Yoho National Park of Canada.jpg
Satellite image of the area.

The fossil-bearing deposits of the Burgess Shale correlate to the Stephen Formation, a collection of slightly calcareous dark mudstones, about 508 million years old. [6] The beds were deposited at the base of a cliff about 160 m tall, [6] below the depth agitated by waves during storms. [11] This vertical cliff was composed of the calcareous reefs of the Cathedral Formation, which probably formed shortly before the deposition of the Burgess Shale. [6] The precise formation mechanism is not known for certain, but the most widely accepted hypothesis suggests that the edge of the Cathedral Formation reef became detached from the rest of the reef, slumping and being transported some distance – perhaps kilometers – away from the reef edge. [6] Later reactivation of faults at the base of the formation led to its disintegration from about 509  million years ago. [12] This would have left a steep cliff, the bottom of which would be protected from tectonic decompression because the limestone of the Cathedral Formation is difficult to compress. This protection explains why fossils preserved further from the Cathedral Formation are impossible to work with – tectonic squeezing of the beds has produced a vertical cleavage that fractures the rocks, so they split perpendicular to the fossils. [6] The Walcott quarry produced such spectacular fossils because it was so close to the Stephen Formation – indeed the quarry has now been excavated to the very edge of the Cambrian cliff. [6]

It was originally thought that the Burgess Shale was deposited in anoxic conditions, but mounting research shows that oxygen was continually present in the sediment. [13] The anoxic setting had been thought to not only protect the newly dead organisms from decay, but it also created chemical conditions allowing the preservation of the soft parts of the organisms. Further, it reduced the abundance of burrowing organisms – burrows and trackways are found in beds containing soft-bodied organisms, but they are rare and generally of limited vertical extent. [6] Brine seeps are an alternative hypothesis; see Burgess Shale type preservation for a more thorough discussion.

Stratigraphy

Walcott Quarry of the Burgess Shale showing the Walcott Quarry Shale Member. The white parallel vertical streaks are remnants of drill holes made during excavations in mid-1990s. WalcottQuarry080509.jpg
Walcott Quarry of the Burgess Shale showing the Walcott Quarry Shale Member. The white parallel vertical streaks are remnants of drill holes made during excavations in mid-1990s.

The Burgess Shale Formation comprises 10 members, the most famous being the Walcott Quarry Shale Member comprising the greater phyllopod bed. [11]

Taphonomy and diagenesis

[14] [15] [16] [17] [18] [19]

There are many other comparable Cambrian lagerstätten ; indeed such assemblages are far more common in the Cambrian than in any other period. This is mainly due to the limited extent of burrowing activity; as such bioturbation became more prevalent throughout the Cambrian, environments capable of preserving organisms' soft parts became much rarer. [6] (The pre-Cambrian fossil record of animals is sparse and ambiguous, cf ediacaran biota.)

Biota

The biota of the Burgess Shale appears to be typical of middle Cambrian deposits. [6] Although the hard-part bearing organisms make up as little as 14% of the community, [6] these same organisms are found in similar proportions in other Cambrian localities. This means that there is no reason to assume that the organisms without hard parts are exceptional in any way; many appear in other lagerstätten of different age and locations. [6]

The biota consists of a range of organisms. Free-swimming (nectonic) organisms are relatively rare, with the majority of organisms being bottom dwelling (benthic) — either moving about (vagrant) or permanently attached to the sea floor (sessile). [6] About two-thirds of the Burgess Shale organisms lived by feeding on the organic content in the muddy sea floor, while almost a third filtered out fine particles from the water column. Under 10% of organisms were predators or scavengers, although since these organisms were larger, the biomass was split equally among each of the filter feeding, deposit feeding, predatory and scavenging organisms. [6]

Many Burgess Shale organisms represent stem group members of the modern animal phyla, though crown group representatives of certain phyla are also present. [20]

A comprehensive list can be found at Paleobiota of the Burgess Shale.

Working with the Burgess Shale

The fossils of the Burgess Shale are preserved as black carbon films on black shales, and so are difficult to photograph; however, various photographic techniques can improve the quality of the images that can be acquired. [21] Other techniques include backscatter SEM, elemental mapping and camera lucida drawing.

Once images have been acquired, the effects of decay and taphonomy must be accounted for before a correct anatomical reconstruction can be made. A consideration of the combination of characters allows researchers to establish the taxonomic affinity.

See also

Related Research Articles

<i>Hallucigenia</i> Genus of Cambrian animals

Hallucigenia is a genus of lobopodian, known from Cambrian aged fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. Lobopodians are a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose.

<span class="mw-page-title-main">Maotianshan Shales</span> Series of Early Cambrian deposits in the Chiungchussu Formation

The Maotianshan Shales (帽天山页岩) are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation, famous for their Konservat Lagerstätten, deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shales form one of some forty Cambrian fossil locations worldwide exhibiting exquisite preservation of rarely preserved, non-mineralized soft tissue, comparable to the fossils of the Burgess Shale of British Columbia, Canada. They take their name from Maotianshan Hill in Chengjiang County, Yunnan Province, China.

<i>Marrella</i> Extinct genus of Arthropods

Marrella is an extinct genus of marrellomorph arthropod known from the Middle Cambrian of North America and Asia. It is the most common animal represented in the Burgess Shale of British Columbia, Canada, with tens of thousands of specimens collected. Much rarer remains are also known from deposits in China.

<i>Pikaia</i> Extinct genus of primitive chordates

Pikaia gracilens is an extinct, primitive chordate animal known from the Middle Cambrian Burgess Shale of British Columbia. Described in 1911 by Charles Doolittle Walcott as an annelid, and in 1979 by Harry B. Whittington and Simon Conway Morris as a chordate, it became "the most famous early chordate fossil", or "famously known as the earliest described Cambrian chordate". It is estimated to have lived during the latter period of the Cambrian explosion. Since its initial discovery, more than a hundred specimens have been recovered.

<i>Wiwaxia</i> Genus of Cambrian animals

Wiwaxia is a genus of soft-bodied animals that were covered in carbonaceous scales and spines that protected it from predators. Wiwaxia fossils—mainly isolated scales, but sometimes complete, articulated fossils—are known from early Cambrian and middle Cambrian fossil deposits across the globe. The living animal would have measured up to 5 centimetres (2 in) when fully grown, although a range of juvenile specimens are known, the smallest being 2 millimetres (0.08 in) long.

<i>Ottoia</i> Extinct genus of priapulid worms

Ottoia is a stem-group archaeopriapulid worm known from Cambrian fossils. Although priapulid-like worms from various Cambrian deposits are often referred to Ottoia on spurious grounds, the only clear Ottoia macrofossils come from the Burgess Shale of British Columbia, which was deposited 508 million years ago. Microfossils extend the record of Ottoia throughout the Western Canada Sedimentary Basin, from the mid- to late- Cambrian. A few fossil finds are also known from China.

<i>Waptia</i> Cambrian arthropod

Waptia is an extinct genus of arthropod from the Middle Cambrian of North America. It grew to a length of 6.65 cm (3 in), and had a large bivalved carapace and a segmented body terminating into a pair of tail flaps. It was an active swimmer and likely a predator of soft-bodied prey. It is also one of the oldest animals with direct evidence of brood care. Waptia fieldensis is the only species classified under the genus Waptia, and is known from the Burgess Shale Lagerstätte of British Columbia, Canada. Specimens of Waptia are also known from the Spence Shale of Utah, United States.

<i>Dinomischus</i>

Dinomischusis an extinct genus of stalked filter-feeding animals with the Cambrian period, with specimens known from the Burgess Shale and the Maotianshan Shales. While long of uncertain affintiies, recent studies have suggested it to be a stem-group ctenophore.

The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 69 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion. Additional sites with a similar form of preservation are known from the Ediacaran and Ordovician periods.

A number of assemblages bear fossil assemblages similar in character to that of the Burgess Shale. While many are also preserved in a similar fashion to the Burgess Shale, the term "Burgess Shale-type fauna" covers assemblages based on taxonomic criteria only.

The fossils of the Burgess Shale, like the Burgess Shale itself, are fossils that formed around 505 million years ago in the mid-Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 65,000 specimens in a series of field trips up to the alpine site from 1909 to 1924. After a period of neglect from the 1930s to the early 1960s, new excavations and re-examinations of Walcott's collection continue to reveal new species, and statistical analysis suggests that additional discoveries will continue for the foreseeable future. Stephen Jay Gould's 1989 book Wonderful Life describes the history of discovery up to the early 1980s, although his analysis of the implications for evolution has been contested.

<span class="mw-page-title-main">Stephen Formation</span>

The Stephen Formation is a geologic formation exposed in the Canadian Rockies of British Columbia and Alberta, on the western edge of the Western Canada Sedimentary Basin. It consists of shale, thin-bedded limestone, and siltstone that was deposited during Middle Cambrian time. It is famous for the exceptional preservation of soft-bodied fossils: the Burgess Shale biota. The formation overlies the Cathedral escarpment, a submarine cliff; consequently it is divided into two quite separate parts, the 'thin' sequence deposited in the shallower waters atop the escarpment, and the 'thick' sequence deposited in the deeper waters beyond the cliff. Because the 'thick' Stephen Formation represents a distinct lithofacies, some authors suggest it warrants its own name, and dub it the Burgess Shale Formation. The stratigraphy of the Thin Stephen Formation has not been subject to extensive study, so except where explicitly mentioned this article applies mainly to the Thick Stephen Formation.

<i>Eldonia</i> Extinct genus of soft-bodied animals

Eldonia is an extinct soft-bodied cambroernid animal of unknown affinity, best known from the Fossil Ridge outcrops of the Burgess Shale, particularly in the 'Great Eldonia layer' in the Walcott Quarry. In addition to the 550 collected by Walcott, 224 specimens of Eldonia are known from the Greater Phyllopod bed, where they comprise 0.43% of the community. Species also occur in the Chengjiang biota, Siberia, and in Upper Ordovician strata of Morocco.

<span class="mw-page-title-main">History of the Burgess Shale</span>

The Burgess Shale, a series of fossil beds in the Canadian Rockies, was first noticed in 1886 by Richard McConnell of the Geological Survey of Canada (GSC). His and subsequent finds, all from the Mount Stephen area, came to the attention of palaeontologist Charles Doolittle Walcott, who in 1907 found time to reconnoitre the area. He opened a quarry in 1910 and in a series of field trips brought back 65,000 specimens, which he identified as Middle Cambrian in age. Due to the quantity of fossils and the pressures of his other duties at the Smithsonian Institution, Walcott was only able to publish a series of "preliminary" papers, in which he classified the fossils within taxa that were already established. In a series of visits beginning in 1924, Harvard University professor Percy Raymond collected further fossils from Walcott's quarry and higher up on Fossil Ridge, where slightly different fossils were preserved.

The Phyllopod bed, designated by USNM locality number 35k, is the most famous fossil-bearing member of the Burgess Shale fossil Lagerstätte. It was quarried by Charles Walcott from 1911–1917, and was the source of 95% of the fossils he collected during this time; tens of thousands of soft-bodied fossils representing over 150 genera have been recovered from the Phyllopod bed alone.

Cambrorhytium is an enigmatic fossil genus known from the Latham Shale (California), and the Chengjiang (China) and Burgess Shale lagerstätte. 350 specimens of Cambrorhytium are known from the Greater Phyllopod bed, where they comprise 0.7% of the community.

<i>Pollingeria</i>

Pollingeria is a problematic genus of animals of the Middle Cambrian Burgess Shale. 3080 specimens of Pollingeria are known from the Greater Phyllopod bed, where they comprise 5.85% of the community.

The Mount Stephen trilobite beds are a series of fossil strata on Mount Stephen, British Columbia that contain exceptionally preserved fossil material. Part of the same stratigraphic unit as the Burgess Shale deposit, many non-mineralized parts are preserved; in addition, a high density of trilobite fossils is present.

<span class="mw-page-title-main">Walcott Quarry</span> Quarry in British Columbia, Canada

The Walcott Quarry is the most famous quarry of the Middle Cambrian Burgess Shale, located in the Canadian Rockies of British Columbia, bearing the Phyllopod beds. This lies at the base of the Walcott Quarry member, on a ridge between Wapta Mountain and Mount Field, and three other quarries – the Raymond, UE and EZ – lie above it. The quarry's proximity to the Cathedral escarpment led to the preservation of spectacular fossils.

<span class="mw-page-title-main">Paleobiota of the Burgess Shale</span>

This is a list of the biota of the Burgess Shale, a Cambrian lagerstätte located in Yoho National Park in Canada.

References

  1. ↑ Lexicon of Canadian Geological Units. "Burgess Shale". Archived from the original on 11 January 2013. Retrieved 6 February 2009.
  2. ↑ Butterfield, N. J. (1 February 2003). "Exceptional Fossil Preservation and the Cambrian Explosion". Integrative and Comparative Biology. 43 (1): 166–177. doi: 10.1093/icb/43.1.166 . ISSN   1540-7063. PMID   21680421.
  3. ↑ Gabbott, Sarah E. (2001). "Exceptional Preservation". eLS. doi:10.1038/npg.els.0001622. ISBN   978-0-470-01590-2.{{cite book}}: |journal= ignored (help)
  4. ↑ Butterfield, N.J. (2006). "Hooking some stem-group" worms": fossil lophotrochozoans in the Burgess Shale". BioEssays . 28 (12): 1161–6. doi:10.1002/bies.20507. PMID   17120226. S2CID   29130876.
  5. ↑ "Charles Walcott". Royal Ontario Museum. Archived from the original on 6 June 2013. Retrieved 29 August 2013.
  6. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Briggs, D. E. G.; Erwin, D. H.; Collier, F. J. (1995), Fossils of the Burgess Shale , Washington: Smithsonian Inst Press, ISBN   1-56098-659-X, OCLC   231793738
  7. ↑ Simon Conway Morris (1998). The Crucible of Creation: The Burgess Shale and the Rise of Animals. Oxford University Press. p.  316. ISBN   978-0-19-286202-0.
  8. ↑ Ward, Peter Douglas; Brownlee, Donald (2003), The life and death of planet Earth: how the new science of astrobiology charts the ultimate fate of our world, Macmillan, ISBN   0-8050-7512-7
  9. ↑ "New fossil bed found by scientists hailed as 'motherlode'". Canada. 11 February 2014. Archived from the original on 2 August 2023. Retrieved 2 August 2023.
  10. ↑ "The First 100 IUGS Geological Heritage Sites" (PDF). IUGS International Commission on Geoheritage. IUGS. Archived (PDF) from the original on 27 October 2022. Retrieved 13 November 2022.
  11. 1 2 Gabbott, S.E.; Zalasiewicz, J.; Collins, D. (2008). "Sedimentation of the Phyllopod bed within the Cambrian Burgess Shale Formation of British Columbia". Journal of the Geological Society . 165 (1): 307–318. Bibcode:2008JGSoc.165..307G. doi:10.1144/0016-76492007-023. S2CID   128685811.
  12. ↑ Collom, C. J.; Johnston, P. A.; Powell, W. G. (2009). "Reinterpretation of 'Middle' Cambrian stratigraphy of the rifted western Laurentian margin: Burgess Shale Formation and contiguous units (Sauk II Megasequence); Rocky Mountains, Canada". Palaeogeography, Palaeoclimatology, Palaeoecology. 277 (1–2): 63–85. Bibcode:2009PPP...277...63C. doi:10.1016/j.palaeo.2009.02.012.
  13. ↑ Powell, W. (2009). "Comparison of Geochemical and Distinctive Mineralogical Features Associated with the Kinzers and Burgess Shale Formations and their Associated Units". Palaeogeography, Palaeoclimatology, Palaeoecology. 277 (1–2): 127–140. Bibcode:2009PPP...277..127P. doi:10.1016/j.palaeo.2009.02.016.
  14. ↑ Butterfield, N.J. (1990). "Organic Preservation of Non-Mineralizing Organisms and the Taphonomy of the Burgess Shale". Paleobiology . 16 (3): 272–286. Bibcode:1990Pbio...16..272B. doi:10.1017/S0094837300009994. JSTOR   2400788. S2CID   133486523.
  15. ↑ Page, Alex; Gabbott, Sarah; Wilby, Phillip R.; Zalasiewicz, Jan A (2008). "Ubiquitous Burgess Shale–style "clay templates" in low-grade metamorphic mudrocks". Geology . 36 (11): 855–858. Bibcode:2008Geo....36..855P. doi:10.1130/G24991A.1.
  16. ↑ Orr, Patrick J.; Briggs, Derek E. G.; Kearns, Stuart L. (1998). "Cambrian Burgess Shale Animals Replicated in Clay Minerals". Science . 281 (5380): 1173–1175. Bibcode:1998Sci...281.1173O. doi:10.1126/science.281.5380.1173. PMID   9712577.
  17. ↑ Caron, Jean-Bernard; Jackson, Donald A. (2006). "Taphonomy of the Greater Phyllopod Bed Community, Burgess Shale". PALAIOS. 21 (5): 451–465. Bibcode:2006Palai..21..451C. doi:10.2110/palo.2003.P05-070R. S2CID   53646959.
  18. ↑ Gaines, R.R.; Kennedy, M.J.; Droser, M.L. (2005). "A new hypothesis for organic preservation of Burgess Shale taxa in the middle Cambrian Wheeler Formation, House Range, Utah". Palaeogeography, Palaeoclimatology, Palaeoecology . 220 (1–2): 193–205. Bibcode:2005PPP...220..193G. doi:10.1016/j.palaeo.2004.07.034.
  19. ↑ Butterfield, N.J.; Balthasar, U.; Wilson, L.A. (2007). "Fossil Diagenesis in the Burgess Shale". Palaeontology. 50 (3): 537–543. Bibcode:2007Palgy..50..537B. doi: 10.1111/j.1475-4983.2007.00656.x .
  20. ↑ e.g. Smith, Martin R.; Caron, Jean-Bernard (2015). "Hallucigenia's head and the pharyngeal armature of early ecdysozoans". Nature. 523 (7558): 75–8. Bibcode:2015Natur.523...75S. doi:10.1038/nature14573. PMID   26106857. S2CID   205244325.
  21. ↑ Bengtson, Stefan (2000). "Teasing Fossils out of Shales with Cameras and Computers" (PDF). Palaeontologia Electronica. 3 (1). Archived (PDF) from the original on 9 October 2022. Retrieved 3 December 2010.

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