Burgess shale type fauna


Burgess shale type fauna

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.cite journal
title = Post-Cambrian Closure of the Deep-Water Slope-Basin Taphonomic Window
author = Orr, P.
year = 2003
journal = Geology
volume = 31
pages = 769
doi = 10.1130/G19193.1
]

Extent

The fauna of the middle Cambrian has a cosmopolitan range.. All assemblages preserving soft-part anatomy have a very similar fauna, even though they span almost every continent.cite journal
doi = 10.1016/j.gr.2007.09.001
title = A preliminary note on the dispersal of the Cambrian Burgess Shale-type faunas
year = 2008
author = Han, J
journal = Gondwana Research
volume = 14
pages = 269
] The wide distribution has been attributed to the advent of pelagic larvae.

Composition

The fauna is composed of a range of soft bodied organisms; creatures with hard, mineralised skeletons are rare, although trilobites are quite commonly found. The major soft-bodied groups are sponges, palaeoscolecid worms,
lobopods, arthropods and anomalocaridids. Assemblages are typically diverse, with the most famous localities each containing in the region of 150 described species.The fauna of the Burgess Shale lived in the photic zone, as bottom-dwelling photosynthesisers are present in the assemblage.citation
author = Parker, A. R.
year = 1998
journal = Proceedings of the Royal Society B: Biological Sciences
volume = 265
issue = 1400
pages = 967–972
url = http://journals.royalsociety.org/index/WMHTRBY5FPJJ4UCH.pdf
publisher = The Royal Society
]

Example faunas

irius Passet fauna

s or molluscs.

"Halkieria" has features associated with more than one living phylum, and is discussed below.

The strangest-looking animals from Sirius Passet are " Pambdelurion " and " Kerygmachela". They are generally regarded as anomalocarids because they have long, soft, segmented bodies with a pair of broad fin-like flaps on most segments and a pair of segmented appendages at the rear. The outer parts of the top surfaces of the flaps have grooved areas which are thought to have acted as gills. Under each flap there is a short, fleshy leg. This arrangement suggests the animals are related to biramous arthropods.Citation
first =G.E.
last =Budd
editor-last =Fortey
editor-first =R.A.
editor2-last =Thomas
editor2-first =R.H.
contribution =Stem Group Arthropods from the Lower Cambrian Sirius Passet Fauna of North Greenland
title =Arthropod Relationships – Special Volume Series 55
year =1997
publisher =Systematics Association
]

Chengjiang fauna

There are several Cambrian fossil sites in the Chengjiang county of China’s Yunnan province. The most significant is the Maotianshan shale, a lagerstätte which preserves soft tissues very well. The Chengjiang fauna date to between 525 million and 520 million years ago, about the middle of the early Cambrian epoch, a few million years after Sirius Passet and at least 10 million years earlier than the Burgess Shale.

The Chengjiang sediments provide what are currently the oldest known chordates, the phylum to which all vertebrates belong. The 8 chordate species include "Myllokunmingia", possibly a very primitive agnathid (jawless fish) and "Haikouichthys", which may be related to lampreys. [cite journal
author =Shu, D-G, Luo, H-L, Conway Morris, S., Zhang X-L, Hu, S-X, Chen, L., Han, J., Zhu, M., Li, Y, Chen, L-Z
title =Lower Cambrian Vertebrates from South China
journal =Nature
volume =402
pages =42–46
date =1999
doi =10.1038/46965
year =1999
] "Yunnanozoon" may be the oldest known hemichordate (a phylum closely related to chordates). [cite journal
author =Shu, D., Zhang, X. and Chen, L.
title =Reinterpretation of Yunnanozoon as the earliest known hemichordate
journal =Nature
volume =380
pages =428–430
date =1996
doi =10.1038/380428a0
year =1996
]

"Anomalocaris" was a mainly soft-bodied swimming predator which was gigantic for its time (up to 70 cm = 2¼ feet long; some later species were 3 times as long); the soft, segmented body had a pair of broad fin-like flaps along each side, except that the last 3 segments had a pair of “fans” arranged in a “V” shape. Unlike "Kerygmachela" and "Pambdelurion" (see above), "Anomalocaris" apparently had no legs, and the grooved patches which are thought to have acted as gills were at the bases of the flaps, or even overlapping on to its back. The two eyes were on relatively long horizontal stalks; the mouth lay under the head and was a round-cornered square of plates which could not close completely; and in front of the mouth were two jointed appendages which were shaped like a shrimp’s body, curved backwards and with short spines on the inside of the curve. "Amplectobelua", also found at Chengjiang, was similar, smaller than "Anomalocaris" but considerably larger than most other Chengjiang animals. Both are thought to have been powerful predators.

"Hallucigenia" looks like a long-legged caterpillar with spines on its back, and almost certainly crawled on the seabed.cite book
author =Conway Morris, S.
title =The Crucible of Creation
publisher =Oxford University Press
date =1998
]

Nearly half of the Chengjiang fossil species are arthropods, few of which had the hard, mineral-reinforced exoskeletons found in most later marine arthropods; only about 3% of the organisms known from Chengjiang have hard shells, and most of those are trilobites (although "Misszhouia" is a "soft-bodied" trilobite). Many other phyla are found there: Porifera (sponges) and Priapulida (burrowing “worms” which were ambush predators), Brachiopoda (these had bivalve-like shells, but fed by means of a lophophore, a fan-like filter which occupied about of half of the internal space), Chaetognatha (arrow worms), Cnidaria (jellyfish, sea anemones), Ctenophora (comb jellies), Echinodermata (starfish, sea urchins, etc.), Hyolitha (enigmatic animals with small conical shells), Nematomorpha (horse hair worms, parasites which are typically about 1 m long and 1 mm to 3 mm in diameter), Phoronida (horseshoe worms which live in chitinous tubes and feed by means of a lophophore), and Protista (single-celled animals). [cite book
author =Hou, X-G., Aldridge, R.J., Bengstrom, J, Siveter, D.J., Feng, X-H
title =The Cambrian Fossils of Chengjiang, China
publisher =Blackwell Science Ltd
date =2004
location =
pages =233
]

Burgess Shale

The Burgess Shale was the first of the Cambrian lagerstätten to be discovered (by Walcott in 1909), and the re-analysis of the Burgess Shale by Whittington and others in the 1970s was the basis of Gould’s book " Wonderful Life", which was largely responsible for non-scientists' awareness of the Cambrian explosion. The fossils date from the mid Cambrian, about 515 million years ago and 10 million years later than the Chengjiang fauna.

The most common Burgess Shale fossils are arthropods, but many of them are unusual and difficult to classify, for example:
*"Marrella" is the most common fossil (see picture above), but Whittington’s re-analysis showed that it belonged to none of the known marine arthropod groups (trilobites, crustaceans, chelicerates; well-known modern chelicerates include spiders and scorpions).cite journal
author =Whittington, H.B.
title =Redescription of "Marrella splendens" (Trilobitoidea) from the Burgess Shale, Middle Cambrian, British Columbia
journal =Geological Survey of Canada Bulletin
volume =209
pages =1–24
date =1971
]
*"Yohoia" was a tiny animal (7 mm to 23 mm long) with: a head shield; a slim, segmented body covered on top by armor plates; a paddle-like tail; 3 pairs of legs under the head shield; a "single" flap-like appendage fringed with setae (bristles) under each body segment, probably used for swimming and/or respiration; a pair of relatively large appendages at the front of the head shield, each with a pronounced “elbow” and ending in four long spines which may have functioned as “fingers”. "Yohoia" is assumed to been a mainly benthic (bottom-dwelling) creature that swam just above the ocean floor and used its appendages to scavenge or capture prey. It may be a member of the arachnomorphs, a group of arthropods that includes the chelicerates and trilobites. [cite book
author =Briggs, D., Erwin, D. and Collier, F.
title =The Fossils of the Burgess Shale
publisher =Smithsonian Books
date =1994
]
*"Naraoia" was a soft-bodied animal (no mineralized parts) which is classified as a trilobite because its appendages (legs, mouth-parts) are very similar.
*"Waptia", "Canadaspis" and "Plenocaris" had bivalve-like carapaces. It is uncertain whether these animals are related or acquired bivalve-like carapaces by convergent evolution. [cite conference
author =Taylor, R.S.
title ='Waptiid' Arthropods and the Significance of Bivalved Carapaces in the Lower Cambrian
booktitle =Palaeontological Association 44th Annual Meeting
date =1999
]

"Pikaia" resembled the modern lancelet, and was the earliest known chordate until the discovery of the fish-like "Myllokunmingia" and "Haikouichthys" among the Chengjiang fauna.

But the “weird wonders”, creatures that resembled nothing known in the 1970s, attracted the most publicity, for example:
*Whittington’s first presentation about "Opabinia" made the audience laugh. [ [http://www.newscientist.com/article/mg12717294.000-palaeontologys-hidden-agenda-spectacular-fossils-from-thetime-when-animals-began-to-build-skeletons-suggest-that-the-fossil-recordisnot-a-perfect-guide-to-the-way-life-evolved-the-fossils-we-cannot-findarejust-as-important-as-those-we-can-.html Palaeontology’s hidden agenda] ] The reconstruction showed a soft-bodied animal with: a slim, segmented body; a pair of flap-like appendages on each segment with gills above the flaps, except that the last 3 segments had no gills and the flaps formed a tail; "five" stalked eyes; a "backward"-facing mouth under the head; a long, flexible, hose-like proboscis which extended from under the front of the head and ended in a “claw” fringed with spines. Subsequent research has concluded that "Opabinia" is a lobopod, closely related to the arthropods and possibly even closer to ancestors of the arthropods. [cite journal
author=Budd, G.E.
title =The morphology of "Opabinia regalis" and the reconstruction of the arthropod stem-group
journal =Lethaia
volume =29
pages =1–14
date =1996
doi =10.1111/j.1502-3931.1996.tb01831.x
year =1996
]
*"Anomalocaris" and "Hallucigenia" were first found in the Burgess Shale, but older specimens have been found in the Chengjiang fauna. They are now regarded as lobopods, and "Anomalocaris" is very similar to "Opabinia" in most respects (except the eyes and feeding mechanisms) – see above.
*"Odontogriphus" is currently regarded as either a mollusc or a lophotrochozoan, i.e. fairly closely related to the ancestors of molluscs (see above).

Other faunas

"Please help by expanding this section"

Other faunas include the Middle Cambrian Wheeler formation of Utah,cite journal
doi = 10.1016/j.palaeo.2004.07.034
title = A New Hypothesis for Organic Preservation of Burgess Shale Taxa in the Middle Cambrian Wheeler Formation, House Range, Utah
year = 2005
author = Gaines, R
journal = Palaeogeography Palaeoclimatology Palaeoecology
volume = 220
pages = 193
] ...

References


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