Cloudina

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Cloudina
Reconstruction of Cloudina

Reconstruction of Cloudina

Temporal occurrence
Ediacarium
Locations
Systematics
Multicellular animals (Metazoa)
Cloudina
Scientific name
Cloudina
Germs , 1972
species
  • Cloudina hartmannae
  • Cloudina riemkeae
  • Cloudina Lucianoi
  • Cloudina sinensis
  • Cloudina carinata

Cloudina is an extinct animal genus of uncertain taxonomic classification that lived in the late Ediacarian anddied out againin the Lower Cambrian . It belongs to the family of Cloudinidae named after it.

etymology

The generic name Cloudina honors the geologist and paleontologist Preston Cloud .

Initial description

Cloudina was first scientifically described in 1972 by Gerard JB Germs .

Occurrence

Cloudina has a wide geographical distribution. The occurrence of the fossil is linked to calcium carbonate- rich sections of stromatolite reefs , in which it occurs together with Namacalathus , a solitary organism like Cloudina, only moderately mineralized, and with Namapoika , a robust skeleton-builder that grows on open surfaces.

In addition to the type locality ( Kuibis Subgroup and Schwarzrand Subgroup , Nama Group in Namibia ; see e.g. Driedoornvlagte ), Cloudina can be found at the following sites:

Socialization

In addition to its association with Namacalathus , Namapoika and Sinotubulites , Cloudina can be found in Siberia with the Anabaritidae and the tabular agglutinating skeleton formers Platysolenites and Spirosolenites .

morphology

Section of Cloudina , in orange the living space of the fossil within the stacked calcite cones

Cloudina is made up of a series of conical tubes made of calcite , one inside the other , whose exact, original composition can no longer be determined. The fossil measures between 0.3 and 6.5 millimeters in diameter and between 8 and 150 millimeters in length. Every single one of the approximately equally dimensioned, downwardly tapering segment cones sits eccentrically in the predecessor below. This arrangement results in a somewhat rigid appearance. Viewed as a whole, the tube arrangement is usually slightly curved or twisted, but can occasionally even have branches. The wall thickness of the tubes is only 8 to 50 μm , on average 10 to 25 μm. Initially it was assumed that the individual tubes had a test tube-like bottom. However, more detailed investigations have now shown that the tubes are open at the bottom. There is also evidence that the tubes were pliable.

Taxonomy

A taxonomic classification of Cloudina has proven to be very difficult. Originally the fossil was placed among the polychaeta . Germs (1972) interpreted it as Cribricyathea , a class from the Lower Cambrian. Glaessner (1976) followed this interpretation, but at the same time pointed out the similarity with the annelid worms (Annelida) and especially the tube worms . Hahn and Pfug (1985) and Conway Morris and colleagues (1990), however, were skeptical of these two points of view and refused to accept an interpretation that went beyond the Cloudinidae family. Some Cloudina hartmannae fossils show buds, suggesting an asexual mode of reproduction. Grant (1990) therefore classified Cloudina as a coral-like cnidarians (Cnidaria). However, since the tubes are open at the bottom and thus represent a non-subchambered, coherent living space, Cloudina is more likely to be viewed as a core group of multi-bristles - so to speak, as evolving aunts or cousins, more recent multi-bristles. This interpretation is supported by the even distribution of boreholes left by predatory organisms. As with so many members of the Ediacara biota , a classification in the Tree of Life is ultimately not possible with Cloudina and a classification into levels between kingdom and family makes little sense.

The following species of the genus Cloudina are known to date :

  • Cloudina hartmannae Germs, 1972
  • Cloudina riemkeae Germs, 1972
  • Cloudina lucianoi (Beurlen and Sommer, 1957) Zaine and Fairchild, 1985
  • Cloudina sinensis Zhang, Li and Dung, 1992
  • Cloudina carinata Cortijo, Musa, Jensenia and Palacios, 2009

Synonyms of Cloudina lucianoi are Aulophycus lucianoi Beurlen and Sommer, 1957 and Cloudina waldei Hahn und Pflug, 1985 .

Habitat and way of life

Fossil discoveries by Cloudina in the Nama Group in Namibia suggest that Cloudina was one of the first reef builders of the fossil record .

Cloudina is usually associated with microbial stromatolites of the shallow water area. Isotope studies of the stromatolites, in particular their calcium / magnesium ratio, indicate relatively cool water temperatures. Cloudina but may also in normal sea floor sediments occur and thus is not a way of life in microbes hills ( Engl. Microbial mounds ) limited. Strangely enough, Cloudina is rarely found in the same position as other soft-body fossils of the Ediacara biota, but rather alternates with them. This shows that the two groups of organisms preferred different environmental conditions.

In many specimens of Cloudina , the ribs formed by the individual cones have different widths, which indicates a variable growth rate. Adolf Seilacher believes that Cloudina was attached to microbe mats . The different growth phases document how the organism kept pace with the background sedimentation - with new cones growing through the freshly deposited sediment so as not to be spilled by it. Bends in the resulting tube can be traced back to a deviation of the microbe mats from the horizontal.

Because of their small size, it would actually be expected that fossils from Cloudina would be found in their living position in the midst of the microbial mats, especially when the sediment rain is constantly falling. However, this is not the case, all of the specimens discovered so far have been washed out of their original habitat. The boreholes of predatory organisms also seem to speak against Seilacher's hypothesis, since they are not concentrated at the head end protruding from the sediment, but are distributed over the entire organism.

According to another theory, Cloudina was sitting on seaweed. As long as no specimen is known in a clear position in life, no final judgment can be made about the real way of life.

Cloudina tubes often form colonies, but they can also occur sporadically. The frequent occurrence of large and occasionally monospecific colonies has been linked to the absence of predatory organisms. Nevertheless, at some sites, up to 20% of the fossils can be infested by boreholes with a diameter of 15 to 400 μm. The holes are distributed fairly regularly along the length of the tube. Some of the tubes have been drilled multiple times - this means that the organism was able to survive an infestation. The animal might be able to shift its position inside the tube because it filled the entire length, but not the full width of the tube. The even distribution of the boreholes cannot be reconciled with an infaunal lifestyle in the midst of microbial mats. Miller's suggestion that Cloudina lived on seaweed or in a reef habitat does not seem so absurd. If modern mollusks are used as a comparison, the size distribution of the holes suggests a predator of the same dimension as Cloudina .

Paleontological importance

Even if Cloudina is not the oldest taxon among the Small Shelly Fauna (SSF), the real significance of the fossil lies more in its widespread distribution. The evolutionary innovation of an outer shell in the course of the Ediacarium is explained as protection against enemies - it practically started an arms race among the multicellular organisms of that time. Boreholes are common in Cloudina , whereas the very similar taxon Sinotubolites , which occasionally occurs in association with Cloudina on the same stratum surface, is free from such an infestation. In addition, the hole diameter is proportional to the size of the host animal - this means that the predators were selective in choosing their victims. These indications of selective infestation underline the hypothesis of speciation as a response to predatory organisms, which is used as a possible explanation of the rapid species explosion in the Lower Cambrian ( Cambrian explosion ).

See also

Individual evidence

  1. ^ A b c Germs, GJB: New shelly fossils from Nama Group, South West Africa . In: American Journal of Science . tape 272 (8) , 1972, pp. 752-761 , doi : 10.2475 / ajs.272.8.752 .
  2. ↑ Yochelson, EL and Stump, E .: Discovery of Early Cambrian Fossils at Taylor Nunatak, Antarctica . In: Journal of Paleontology . tape 51 (4) , 1977, pp. 872-875 .
  3. ^ Zaine, MF and Fairchild, TR: Comparison of Aulophycus lucianoi Beurlen & Sommer from Ladario (MS) and the genus Cloudina Germs, Ediacaran of Namibia . In: Anais Academia Brasileira de Ciencias . tape 57 , 1985, pp. 130 .
  4. ↑ a b Bengtson, S. and Zhao, Y .: Predatorial Borings in Late Precambrian Mineralized Exoskeletons . In: Science . tape 257 (5068) , 1992, pp. 367-369 , doi : 10.1126 / science.257.5068.367 .
  5. ↑ Hofmann, HJund Mountjoy, EW: namacalathus-Cloudina assemblage in Neoproterozoic Miette Group (Byng formation), British Columbia Canada's oldest shelly fossils . In: Geology . tape 29 (12) , 2001, pp. 1091-1094 , doi : 10.1130 / 0091-7613 (2001) 029 <1091: NCAINM> 2.0.CO; 2 .
  6. ^ Conway Morris, S., Mattes, BW and Chen, M .: The early skeletal organism Cloudina: new occurrences from Oman and possibly China . In: American Journal of Science . tape 290 , 1990, pp. 245-260 .
  7. ^ Boggiani, P. and Gaucher, C .: Cloudina from the Itapucumí Group (Vendian, Paraguay): age and correlations . In: 1st Symposium Neopoterozoic-Early Paleozoic Event in SW Gondwana. Extended abstracts . Sao Paulo 2004, p. 13-15 .
  8. ↑ Palacios, T .: Microfosiles de pared organic del Proterozoico superior (Region central de la Peninsula Iberica) . In: Memorias del Museo Paleontologico de la Universidad de Zaragoza . tape 3 , 1989, pp. 1-91 .
  9. ↑ Gaucher, C. and Speechmann, P .: Grupo Arroyo del Soldado: paleontologia, edad y correlaciones (Vendiano-Cámbrico Inferior, Uruguay) . In: Actas II Congreso Uruguaya de Geologia . Montevideo, Sociedad Uruguaya de Geologia - Facultad de Ciencias (in Spanish) 1998, p. 183-187 .
  10. ^ A b Grant, SW: Shell structure and distribution of Cloudina, a potential index fossil for the terminal Proterozoic . In: American Journal of Science . 290-A (290-A), 1990, pp. 261-294 .
  11. ↑ Hagadorn, JW and Wagoner, B .: Ediacaran fossils from the southwestern Great Basin, United States . In: Journal of Paleontology . tape 74 (2) , 2000, pp. 349 , doi : 10.1666 / 0022-3360 (2000) 074 <0349: EFFTSG> 2.0.CO; 2 .
  12. ↑ Andrey Yu. Zhuravlev, Jose Antonio Gamez Vintaned, and Andrey Yu. Ivantsov: First finds of problematic Ediacaran fossil Gaojiashania in Siberia and its origin . In: Geological Magazine . tape 146 (5) , 2009, pp. 775-780 , doi : 10.1017 / S0016756809990185 .
  13. ↑ a b c Miller, AJ: A Revised Morphology of Cloudina with Ecological and Phylogenetic Implications . 2004.
  14. ↑ Glaessner, M. F: Early Phanerozoic annelid worms and their geological and biological significance . In: Journal of the Geological Society (London) . tape 132 (3) , 1976, pp. 259-275 , doi : 10.1144 / gsjgs.132.3.0259 .
  15. ^ Hahn, G. and HD Pflug: The Cloudinidae n. Fam., Lime tubes from the Vendian and Lower Cambrian . In: Senckenbergiana lethaea . tape 65 , 1985, pp. 413-431 .
  16. ↑ Hua, H., Pratt, BR and Zhang, LUYI: Borings in Cloudina Shells: Complex Predator-Prey Dynamics in the Terminal Neoproterozoic . In: PALAIOS . tape 18 (4-5) , 2003, pp. 454 , doi : 10.1669 / 0883-1351 (2003) 018 <0454: BICSCP> 2.0.CO; 2 .
  17. ↑ Vinn, O. and Zaton, M .: Inconsistencies in Proposed annelid affinities of early biomineralized organism Cloudina (Ediacaran): structural and ontogenetic Evidences . In: Carnets de Géologie . CG2012_A03, 2012, p. 39-47 , doi : 10.4267 / 2042/46095 .
  18. ^ Penny, AM: Ediacaran metazoan reefs from the Nama Group, Namibia . In: Science . tape 344 (6191) , 2014, pp. 1504-1506 , doi : 10.1126 / science.1253393 .
  19. ↑ Domke, Kirk L. et al .: Providing a Palaeoecological and Geochemical Context for Cloudina in Western North America . Ed .: Smith, Martin R. et al. Abstract Volume. International Conference on the Cambrian Explosion. Toronto, Ontario, Canada: The Burgess Shale Consortium 2009, ISBN 978-0-9812885-1-2 .
  20. ↑ Seilacher, A .: Biomat-related lifestyles in the Precambrian . In: PALAIOS (SEPM Society for Sedimentary Geology) . tape 14 (1) , 1999, pp. 86-93 , doi : 10.2307 / 3515363 .
  21. ↑ Bengtson, S .: Early skeletal fossils . In: Lipps, JH and Wagoner, BM Neoproterozoic- Cambrian Biological Revolutions (eds.): Paleontological Society Papers . tape 10 , 2004, p. 67-78 .
  22. ↑ Dzik, J .: The Verdun Syndrome: simultaneous origin of protective armor and infaunal shelters at the Precambrian – Cambrian Transition . In: Geological Society, London, Special Publications . tape 286 , 2007, p. 405-414 , doi : 10.1144 / SP286.30 .