Cloudinidae
| Cloudina Temporal range: Ediacaran
| |
|---|---|
| Scientific classification | |
| Kingdom: | |
| Phylum: | Vologdin 1937
|
| Class: | Vologdin 1961
|
| Order: | Jankauskas 1967
|
| Family: | Cloudinidae |
| Genus: | Cloudina Germs 1972
|
| Species | |
| |
Cloudinids are an extinct animal family containing the genus Cloudina. They formed small conical fossils consisting of one calcareous tube nested within another. What the organism itself looked like remains unknown. Cloudinids were widely distributed. They are quite abundant in some deposits. They are amongst the earliest animals to produce a calcareous shell.
The name Cloudina honors the 20th century geologist and paleontologist Preston Cloud[1].
Morphology
Cloudina varies in size from a diameter of 0.3 to 6.5 mm, and 8 to 150 mm in length.[1]. It consists of a series of stacked vase-like tubes, made from microscopic calcite crystals, probably embedded in an organic matrix. The tube is curved or sinuous, and occasionally branches. The tube walls are 8 to 50 micrometers thick.[citation needed] 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]
Geological significance
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[3] and the rise of readily-fossilised life, currently dated at 542 million years old.[4] The extinctions set the stage for the Cambrian explosion of life-forms.
Exactly what kind of animal the Cloudinids were 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[5] 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. Adolf Seilacher suggests that the organisms adhered to microbial mats, and that the growth phases represented the organism keeping pace with sedimentation - growing through new material deposited on it that would otherwise bury it. Kinks in the developing tube are easily explained by the mat falling slightly from the horizontal.[6] The small size of Cloudina means that it is usually found having been washed out of its place of growth, and until a specimen is found in life position its mode of life is open to debate; it has been suggested that the organism may in fact have dwelt on seaweeds.[7]
Some specimens of Cloudina hartmannae display budding,[1] which implies asexual reproduction.[8]
In some locations, up to 20% of Cloudina fossils contain predatory borings ranging from 15 to 400 µm in diameter.[9][10] 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 co-occuring and very similar shelly fossil Sinotubulites was not affected by borings. In addition, the distribution of borings suggests selection for size.Cite error: A <ref> tag is missing the closing </ref> (see the help page)., China's Dengying Formation[11][10]
, Canada[12], Nevada[13] and Brazil[citation needed].
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) - ^ Gradstein, F.M. (2004). A Geologic Time Scale 2004. Cambridge University Press.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Ca/Mg ratios
- ^ Seilacher, A. (1999). "Biomat-related lifestyles in the Precambrian". Palaios. 14 (1): 86–93.
{{cite journal}}:|access-date=requires|url=(help) - ^ Miller, A.J. (in press?), A Revised Morphology of Cloudina with Ecological and Phylogenetic Implications (PDF), retrieved 2007-04-24
{{citation}}: Check date values in:|year=(help)CS1 maint: year (link) - ^ Hua, H. (2005). "Skeletogenesis and asexual reproduction in the earliest biomineralizing animal Cloudina". Geology. 33 (4): 277–280. Retrieved 2007-04-24.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ 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) - ^ a b Bengtson, S. (1992-07-17). "Predatorial Borings in Late Precambrian Mineralized Exoskeletons". Science. 257 (5068): 367. doi:10.1126/science.257.5068.367. Retrieved 2007-04-24.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Cite error: The named reference
Conway1990was invoked but never defined (see the help page). - ^ Hofmann and Mountjoy, 2001, cited in Miller
- ^ Hagadorn and Waggoner, 2000, cited in Miller