Cloudinidae: Difference between revisions
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==Localities== |
==Localities== |
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First found in the Nama Formation in Namibia, ''Cloudina'' has also been observed in Oman, China's Dengying Formation,<ref name=Conway1990>{{cite journal |
First found in the Nama Formation in Namibia,<ref name=Description /> ''Cloudina'' has also been observed in Oman, China's Dengying Formation,<ref name=Conway1990>{{cite journal |
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| author = Conway Morris, S. |
| author = Conway Morris, S. |
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| coauthors = Mattes, BW, Chen, M. |
| coauthors = Mattes, BW, Chen, M. |
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| accessdate = 2007-04-24 |
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}}</ref>Canada, Nevada and Brazil. |
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Canada, Nevada and Brazil. |
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==References and footnotes== |
==References and footnotes== |
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Revision as of 10:36, 24 April 2007
| Cloudina Temporal range: Ediacaran
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|---|---|
| Scientific classification | |
| Kingdom: | |
| Phylum: | Archaeocyatha Vologdin 1937
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| Class: | Cribriocyathea Vologdin 1961
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| Order: | Pterocyathida Jankauskas 1967
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| Family: | Cloudinidae
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| Genus: | Cloudina Germs 1972
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| Species | |
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Cloudinids (Cloudina) are an extinct animal genus that formed small tubelike or conical fossils consisting of "funnel deeply nested in funnel" segments of calcareous material. What the animal itself looked like is still unknown. Cloudinids were widely distributed. They are quite abundant in some deposits. They are the earliest common animal form with a calcareous shell. The name Cloudina honors the 20th century geologist and paleontologist Preston Cloud. It was first discovered by GJB Germs in 1972.
Cloudina varies in size from a diameter of 0.3 to 6.5 mm, and 8 to 150 mm in length.[1]. It is a tube made from microscopic calcite crystals, that was likely to be embedded in an organic matrix. The tube is curved or sinuous, and occasionally bifurcates. The tube walls are 8 to 50 micrometers thick. Cloudina occurred in calcium carbonate rich areas of stromatolite reefs. It is found with Namacalathus, which like Cloudina was "weakly skeletal" and solitary, and Namapoikia, which was "robustly skeletal" and and formed sheets on open surfaces.[2]
Cloudina are characteristic of the so-called "Small Shelly Fauna" in the final Neoproterozoic period, called the Ediacaran, and disappeared in the extinction event that marks the Precambrian - Cambrian boundary, most recently dated at 542 million years old.[3] The extinctions set the stage for the Cambrian explosion of life-forms.
Exactly what kind of animal it was is unknown; it resembles serpulid polychaete annelid worms and pogonophoran worms, and has similarities to the trace fossils Salterella and Cornulites. Its lack of bilateral or radial symmetry rules out Coelenteratan affinities.
Ecology
The tubes often appear to form colonies, although they are sometimes found in more isolated situations. The assimilation of large, sometimes monospecific, colonies can be attributed to the lack of significant predation.[1]
Cloudina is often found in association with microbial stromatolites which are limited to shallow water; their isotopic composition[4] suggests that water temperatures were relatively cool.
Their growth shows a periodic structure, with new layers added periodically; the ridges formed are often of varying width, suggesting a non-constant growth rate. One specimen of Cloudina hartmannae displays budding,[1] which may suggest asexual reproduction.[citation needed]
Around 20% of Cloudina fossils contain predatory borings 15–85 µm in diameter.[5] The boreholes are distributed along the tube length, mostly not at the top. This may indicate that the animal could retract itself down the tube in response to predation. Interestingly, the very similar co-occuring shelly fossil Sinotubulites was not affected by borings. This evidence of predator-prey specificity shows the possibility of speciation in response to predation, a potential cause of the rapid diversification event during the Cambrian.
Localities
First found in the Nama Formation in Namibia,[1] Cloudina has also been observed in Oman, China's Dengying Formation,[6]Canada, Nevada and Brazil.
References and footnotes
- ^ a b c d Germs, G.J.B. (October 1972). "New shelly fossils from Nama Group, South West Africa". American Journal of Science. 272: 752–761.
- ^ Neoproterozoic Microbial-Metazoan Reefs, Nama Region, Namibia - abstract retrieved January 13, 2007
- ^ Amthor, J.E. (2003). "Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman". Geology. 31 (5): 431–434.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Ca/Mg ratios
- ^ HUA, H. (2003). "Borings in Cloudina Shells: Complex Predator-Prey Dynamics in the Terminal Neoproterozoic". Palaios. Retrieved 2007-04-24.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Conway Morris, S. (1990). "The early skeletal organism Cloudina: new occurrences from Oman and possibly China". American Journal of Science. 290: 245–260.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help)
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