Small shelly fauna

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The small shelly fauna is the name given to an obscure collection of small hard-shelled fossils found worldwide in beds a bit older than the earliest trilobites and archeocyathids from the Nekamit-Daldynian and Tommotian stages (Lower Cambrian). The start of the Cambrian period had classically been set at the first appearance of small shelly fossils. Workers in a remote part of Siberia found very small hard-shelled fossils in slightly older beds in the 1980s. Similar fossils were later found in corresponding beds in many other parts of the world.

The forms included diminutive specimens of known animals such as archeocyathids and brachiopods plus many small shell-like forms a millimeter or two in size. It was later recognized that the latter were fragments of body armor of a few types of animals, not complete shells of a multitude of unknown creatures. Common practice is to include the small shelly fauna in the earliest Lower Cambrian. The fauna and its relationship to more conventional later faunas is still poorly understood.

References

Bengtson, S. 1992: The Cap-Shaped Cambrian Fossil Maikhanella and the Relationship Between Coeloscleritophorans and Molluscs. Lethaia 25: 401-420.
Conway Morris, S. 1997: The Cuticular Structure of the 495-Myr-Old Type Species of the Fossil Worm, Palaeoscolex, P. piscatorum (?Priapulida). Zoological Journal of the Linnaean Society 119: 69-82.
Conway Morris, S.; Peel, J.S. 1995: Articulated Halkieriids from the Lower Cambrian of North Greenland and Their Role in Early Protostome Evolution. Philosophical Transactions of the Royal Society of London, Ser. B Biol. Sci. 347: 305-358.
Grotzinger, John P.; Watters, W.; Knoll, Andrew H.; Smith, O. 1998: Diverse Calcareous Fossils from the Ediacaran-Age Nama Group, Namibia. Abstracts with Programs, Geological Society of America, 20 (7): A-147.
Haas, W. 1981: Evolution of Calcareous Hardparts in Primitive Molluscs. Malacologia, 21: 403-418.
Jacobs, David K.; Wray, Charles G.; Wedeen, Cathy J.; Kostriken, Richard; DeSalle, Rob; Staton, Joseph L.; Gates, Ruth D.; Lindberg, David R. 2000: Molluscan engrailed Expression, Serial Organization, and Shell Evolution. Evolution and Development, 2:6, pp. 340-347.
Matthews, S.C.; Missarzhevsky, V.V. 1975: Small shelly fossils of late Precambrian and early Cambrian age: a review of recent work. Journal of the Geological Society 131: 289-304.
Runnegar, Bruce 1992: Chapter 3 – Evolution of the Earliest Animals. In: Schopf, J. William (ed) Major Events in the History of Life. Jones and Bartlett.
Valentine, James W. 1995: Late Precambrian bilaterians: Grades and clades. In: Fitch, Walter M.; Ayala, Francisco J. 1995: Tempo and mode in evolution: Genetics and paleontology 50 years after Simpson. National Academy of Sciences, pp. 87-107.

External links

http://www.peripatus.gen.nz/Paleontology/SmaSheFau.html small shelly fauna
http://www.peripatus.gen.nz/paleontology/CamExp.html Cambrian explosion
http://hoopermuseum.earthsci.carleton.ca/camex/1jtommo.html Tommotian fauna, images

And see at Tommotian Age#References.

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