Phyllopod bed

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The Phyllopod bed, designated by USNM locality number 35k, [1] is the most famous fossil-bearing member of the Burgess shale fossil Lagerstätte . It was quarried by Charles Walcott from 19111917 (and later named Walcott Quarry), and was the source of 95% of the fossils he collected during this time; [2] tens of thousands of soft-bodied fossils [3] representing over 150 genera [4] have been recovered from the Phyllopod bed alone.

Lagerstätte sedimentary deposit that exhibits extraordinary fossils with exceptional preservation

A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus delaying the decomposition of both gross and fine biological features until long after a durable impression was created in the surrounding matrix. Lagerstätten span geological time from the Neoproterozoic era to the present. Worldwide, some of the best examples of near-perfect fossilization are the Cambrian Maotianshan shales and Burgess Shale, the Devonian Hunsrück Slates and Gogo Formation, the Carboniferous Mazon Creek, the Jurassic Solnhofen limestone, the Cretaceous Santana, Yixian and Tanis formations, the Eocene Green River Formation, and the Miocene Foulden Maar.

Charles Doolittle Walcott American paleontologist

Charles Doolittle Walcott was an American paleontologist, administrator of the Smithsonian Institution from 1907 to 1927, and geologist. He is famous for his discovery in 1909 of well-preserved fossils, including some of the oldest soft-part imprints, in the Burgess Shale of British Columbia, Canada. He was described by Stephen Jay Gould as "the finest symbol that I have ever encountered for the embodiment of conventional beliefs."

Walcott Quarry

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.

Contents

Stratigraphy and location

Fossil Ridge forms the spectacular backdrop to the Phyllopod Bed Fossil Ridge.jpg
Fossil Ridge forms the spectacular backdrop to the Phyllopod Bed

The phyllopod bed is a 2.31 m thick layer of the 7 m thick Greater Phyllopod Bed, [4] found in the Walcott Quarry on Fossil Ridge, between Wapta Mountain and Mount Field, at an elevation of around 2,300 metres (7,500 ft), around 5 kilometres (3.1 mi) north of the railway town of Field, British Columbia, in the Canadian Rocky Mountains. [5] It is adjacent to Mount Burgess, where Walcott first discovered the Burgess Shale formation.

Wapta Mountain Mountain in Yoho NP, BC, Canada

Wapta Mountain is a mountain located in the Canadian Rocky Mountains between Emerald Lake and Yoho Valley in Yoho National Park, British Columbia, Canada. It stands just north of the ridge containing the Burgess Shale fossil beds. Along with The Vice President and Mount Burgess, Wapta Mountain forms the backdrop to Emerald Lake, and marks the southern end of the President Range.

Mount Field (British Columbia) mountain in British Columbia, Canada

Mount Field is a mountain located about 10 km (6 mi) east of the town of Field in Yoho National Park, Canada. The mountain was named in 1884 after Cyrus West Field, an American merchant who had laid the first Atlantic cable, 1858, a second in 1866; Mr. Field was visiting the Canadian Rockies the year as a guest of the CPR who were building the national railway, at the naming of a station and a mountain.

Railway town settlement that was greatly developed because of a railway station or junction at its site

A railway town, or railroad town, is a settlement that originated or was greatly developed because of a railway station or junction at its site.

Walcott divided the bed into twelve units [6] based on the rock type and fossil content. [1] Certain fossil beds provide reference levels and can be recognized by the superabundance of a particular type of fossil: for instance, the Great Marrella layer and Great Eldonia layer. [7]

<i>Marrella</i> genus of arthropods

Marrella splendens is an extinct arthropod known from the middle Cambrian Burgess Shale of British Columbia. It is the most common animal represented in the Burgess Shale.

<i>Eldonia</i> extinct animal genus of unknown affinity

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, and in Upper Ordovician strata of Morocco.

History

Walcott and his team collecting from the Phyllopod bed, c. 1913 Charles Doolittle Walcott (1850-1927), Sidney Stevens Walcott (1892-1977), and Helen Breese Walcott (1894-1965).jpg
Walcott and his team collecting from the Phyllopod bed, c. 1913

After locating soft-bodied fossils in loose fragments of rock in 1907, the Phyllopod bed was located in a source for the fragments' origins by the Walcotts in 1910. [8] Extensive quarrying was performed in field seasons until 1913, and Walcott considered the ton of shale he collected in his next visit, in 1917, to have practically exhausted the productive potential of the bed. [8]

Taphonomy

Most of the organisms within the Phyllopod bed had been transported minimal distances before they were buried, and decayed in place until they were buried (at which time decay and disarticulation was halted). [4] Mineralization of tissues occurred shortly afterwards. [4] The community of organisms preserved is a good representation of the (preservable) community; the biasing effects of time-averaging and preferential decay seem to be minimal. [4] A great deal of compaction occurred after the deposition of the fossils. [7]

Sedimentation

The unit consists of mudstones that intergrade into coarser shelly sandstones that sometimes form small nodules. [7] There are (very rare) turbidite layers, but on the whole the unit was deposited in large events that dumped tens of centimetres of sediment at a time as a slurry of mud was washed over the site by a density current, sweeping up and entombing any organisms in its path. [7]

Preservation

The preservation of the fossils and their pre-burial livelihoods was likely facilitated by mats of the cyanobacterium Morania , which served to bind the sediment and allow anoxic conditions to quickly form. [4]

Community structure

A page of Walcott's field notebook, depicting some familiar fossils from the Phyllopod bed Walcott diary.jpg
A page of Walcott's field notebook, depicting some familiar fossils from the Phyllopod bed

The phyllopod bed preserves a range of organisms from both a rich benthic community (organisms living on and in the sediment) and representatives of the nekton. [9] Many feeding modes are present and a complex food web can be inferred. [9] Whilst some shelly fossils are present (and seem to be typical of any Cambrian shelly fossil assemblage), the majority of fossils - probably 98% of what was alive at the time of burial - do not derive from biomineralized components. [9]

Ichnofauna

Whilst trace fossils or ichnofauna are locally abundant in other areas of the Burgess Shale, they are almost completely absent in the Phyllopod bed, [10] perhaps as a result of the presence of Morania.

Related Research Articles

Burgess Shale Rock formation

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

<i>Amiskwia</i> genus of marine worms

Amiskwia is a genus of large, soft-bodied animals known from fossils of the Middle Cambrian Lagerstätten both in the Burgess shale formation in British Columbia and the Maotianshan shales of Yunnan Province, China. It is interpreted as a member of the Gnathiferan total group.

<i>Pikaia</i> extinct animal

Pikaia gracilens is an extinct, primitive chordate animal known from the Middle Cambrian Burgess Shale of British Columbia. Sixteen specimens are known from the Greater Phyllopod bed, where they comprised 0.03% of the community. It resembled the lancelet and perhaps swam much like an eel.

<i>Peytoia</i> Genus of anomalocarids

Peytoia is a genus of anomalocarids that lived in the Cambrian period, containing two species, Peytoia nathorsti and Peytoia infercambriensis. Its two mouth appendages had long bristle-like spines, it had no fan tail, and its short stalked eyes were behind its mouth appendages.

<i>Odaraia</i>

Odaraia is a genus of crustacean arthropod from the Middle Cambrian. Its fossils, which reach 15 centimetres (5.9 in) in length, have been found in the Burgess Shale in British Columbia, Canada. 217 specimens of Odaraia alata are known from the Greater Phyllopod Bed, where they comprise 0.41% of the community.

The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 40 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.

<i>Canadia</i> (annelid) Species of annelid (fossil)

Canadia is a genus of extinct annelid worm present in Burgess Shale type Konservat-Lagerstätte. It is found in strata dating back to the Delamaran stage of the Middle Cambrian around 505 million years ago, during the time of the Cambrian explosion. It was about 3 centimeters in length. Charles Doolittle Walcott named Canadia in 1911 after Canada, the country from which its remains have been found. 28 specimens of Canadia (annelid) are known from the Greater Phyllopod bed, where they comprise 0.05% of the community.

The fossils of the Burgess Shale, like the Burgess Shale itself, formed around 505 million years ago in the Mid Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 60,000 specimens in a series of field trips up 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 discover new species, and statistical analysis suggests discoveries will continue for the foreseeable future. Stephen Jay Gould's book Wonderful Life describes the history of discovery up to the early 1980s, although his analysis of the implications for evolution has been contested.

Morania is a genus of cyanobacterium preserved as carbonaceous films in the Middle Cambrian Burgess Shale. it is present throughout the shale; 2580 specimens of Morania are known from the Greater Phyllopod bed, where they comprise 4.90% of the community. It is filamentous, forms sheets, and resembles the modern cyanobacterium Nostoc. It would have had a role in binding the sediment, and would have been a food source for such organisms as Odontogriphus and Wiwaxia.

Stephen Formation

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.

History of the Burgess Shale

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.

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>Louisella</i> genus of marine worms

Louisella is a genus of worm known from the Middle Cambrian Burgess Shale. It was originally described by Charles Walcott in 1911 as a holothurian echinoderm, and represents a senior synonym of Miskoia, which was originally described as an annelid. 48 specimens of Louisella are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community. It has been stated to have palaeoscolecid-like sclerites, though this is not in fact the case.

Insolicorypha is a genus of polychaetes known from the Middle Cambrian Burgess Shale. A single specimen of Insolicorypha is known from the Greater Phyllopod bed. The genus was described by Conway Morris (1979) and re-examined by Eibye-Jacobsen (2004).

<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.

Stephenoscolex is a genus of polychaete worm known from the Middle Cambrian Burgess Shale. 150 specimens of Stephenoscolex are known from the Greater Phyllopod bed, where they comprise 0.29% of the community. The genus was described by Conway Morris (1979) and re-examined by Eibye-Jacobsen (2004).

Dark stain

A dark stain is often associated with fossils of the Burgess Shale, representing decay fluids that were squashed out of the organism during the taphonomic process.

References

  1. 1 2 Conway Morris, S. (1977). "A redescription of the Middle Cambrian worm Amiskwia sagittiformis Walcott from the Burgess Shale of British Columbia" (PDF). Paläontologische Zeitschrift. 51 (3–4): 271–287. doi:10.1007/BF02986576. ISSN   0031-0220.
  2. Collins, D.; Briggs, D.; Morris, S. (1983). "New Burgess Shale Fossil Sites Reveal Middle Cambrian Faunal Complex". Science. 222 (4620): 163–167. Bibcode:1983Sci...222..163C. doi:10.1126/science.222.4620.163. PMID   17741659.
  3. Morris, S. C. (1989). "Burgess Shale Faunas and the Cambrian Explosion". Science. 246 (4928): 339–346. Bibcode:1989Sci...246..339C. doi:10.1126/science.246.4928.339. PMID   17747916.
  4. 1 2 3 4 5 6 Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS. 21 (5): 451–65. Bibcode:2006Palai..21..451C. doi:10.2110/palo.2003.P05-070R. JSTOR   20173022.
  5. Whittington, H. B. (16 November 1978). "The Lobopod animal Aysheaia pedunculata Walcott, Middle Cambrian, Burgess Shale, British Columbia". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences . 284 (1000): 165–197. Bibcode:1978RSPTB.284..165W. doi:10.1098/rstb.1978.0061. JSTOR   2418243.
  6. Walcott, C. (1912). "Middle Cambrian Branchiopoda, Malacostraca, Trilobita, and Merostomata". Smithsonian Miscellaneous Collections. Washington, D. C. 57: 145–228.
  7. 1 2 3 4 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. Bibcode:2008JGSoc.165..307G. doi:10.1144/0016-76492007-023.
  8. 1 2 Yochelson, E. L. (1 December 1996). "Discovery, Collection, and Description of the Middle Cambrian Burgess Shale Biota by Charles Doolittle Walcott". Proceedings of the American Philosophical Society. 140 (4): 469–545. ISSN   0003-049X. JSTOR   987289.
  9. 1 2 3 Conway Morris, Simon (1986). "community structure of the Middle Cambrian phyllopod bed (Burgess Shale)" (PDF). Palaeontology. 29 (3): 423–467. Archived from the original (PDF) on 2011-07-16.
  10. Conway Morris, S. (1979). "The Burgess Shale (Middle Cambrian) Fauna". Annual Review of Ecology and Systematics. 10: 327–349. doi:10.1146/annurev.es.10.110179.001551.

Coordinates: 51°26′24″N116°28′12″W / 51.440°N 116.470°W / 51.440; -116.470