Box The chitinozoan Rosetta Stone

But what really were chitinozoans? Material from the Ordovician of Estonia, described as the chitinozoan "Rosetta Stone", may have partially solved the problem. Individual vesicles are linked together in a coiled, chain-like structure; each vesicle belongs to the same species, Desmochitina nodosa Eisenack (Fig. 9.22). It is unlikely that these were eggs of a metazoan, because larvae would be unable to escape from the tightly sealed and connected chambers. Therefore Paris and Nolvak (1999) postulated that the coiled, chain-like structure represents an intermediate, immature stage, perhaps an intra-oviduct phase, prior to the final egg-laying event. Unfortunately, distribution in time and space of chitinozoans does not match any skeletonized metazoan group. So we are back to speculation. Possibly chitinozoans are related to a soft-bodied "chitinozoan animal" and the search is on to find this animal in one or more of the Paleozoic Lagerst├Ątten.

Figure 9.22 Chitinozoan apparatus: a large cluster of Desmochitina nodus interpreted as an egg clutch of the chitinozoan animal; the opercula are not present suggesting that the animals had already hatched (x70). (Courtesy of Florentin Paris.)
Sphaerochitina Urnochitina
Chitinozoan

Conochitina Ancyrochitina

Colonial arrangements

Figure 9.23 Some chitinozoan morphotypes: Sphaerochitina (xl60), Urnochitina (xl60), Conochitina (x80), Ancyrochitina (x240) and colonial arrangements (x40).

Conochitina Ancyrochitina

Colonial arrangements

Figure 9.23 Some chitinozoan morphotypes: Sphaerochitina (xl60), Urnochitina (xl60), Conochitina (x80), Ancyrochitina (x240) and colonial arrangements (x40).

Review questions

1 The move from prokaryote to eukaryote cell types was a major evolutionary jump. How was this transition achieved and what sorts of implications did it have for life on Earth?

2 Foraminifera have been widely used by oil and gas companies in exploration. Why are they so useful?

3 Radiolarians have proved very useful in sorting out the stratigraphy of mountain belts. Why are they superior to other micro- and macrofossil groups in these types of studies?

4 Chromistan groups such as the cocco-lithophores and diatoms have a fundamental effect on the stability of atmospheric and oceanic systems on our planet. But such nannoplankton appeared rela tively late in the geological record. Is there any evidence for a Paleozoic nannoplankton?

5 The identity of the chitinozoans may have been solved but how should these fossils be classified?

Further reading

Armstrong, H.A. & Brasier, M.D. 2005. Microfossils, 2nd edn. Blackwell Publishing, Oxford, UK.

Bignot, G. 1985. Elements of Micropalaeontology. Graham and Trotman, London. (Useful overview of all the main microfossil groups.)

De Wever, P., Dumitrica, P., Caulet, J.P., Nigrini, C. & Caridroit, M. 2001. Radiolarians in the Sedimentary Record. Gordon and Breach Science Publishers, the Netherlands. (Key reference on radiolarian paleontology.)

Haeckel, E. 1862. Die Radiolarien (Rhizopoda Radiaria). Eine Monographie. Reimer, Berlin. (Classic reference on Radiolaria, beautifully illustrated.)

Jenkins, D.G. & Murray, J.W. 1989. Stratigraphical Atlas of Fossil Foraminifera, 2nd edn. British Micropaleontology Association and Ellis Horwood Ltd, London. (Well-illustrated account of the foraminiferans.)

Lipps, J.H. (ed.) 1993. Fossil Prokaryotes and Protists. Blackwell Scientific Publications, Oxford, UK. (Mul-tiauthor compilation of the prokaryote and protist microfossil groups.)

References

Armstrong, H.A. & Brasier, M.D. 2005. Microfossils,

2nd edn. Blackwell Publishing, Oxford, UK. Cavalier-Smith, T. 2002. The phagotrophic origin of eukaryotes and phylogenetic classification of proto zoa. International Journal of Systematic and Evolutionary Microbiology 52, 297-354.

Corsetti, F.A., Olcott, A.N. & Bakermans, C. 2006. The biotic response to Neoproterozoic snowball Earth. Palaeogeography, Palaeoclimatology, Palaeoecology 232, 114-30.

De Wever, P., Dumitrica, P., Caulet, J.P., Nigrini, C. & Caridroit, M. 2001. Radiolarians in the Sedimentary Record. Gordon and Breach Science Publishers, the Netherlands.

Haeckel, E. 1862. Die Radiolarien (Rhizopoda Radiaria). Eine Monographie. Reimer, Berlin.

Haeckel, E. 1904. Kunstformen der Natur. Verlag des Bibliographischen Institut, Leipzig.

Henriksen, K., Young, J.R., Bown, P.R. & Stipp, S.L.S. 2004. Coccolith biomineralisation studied with atomic force microscopy. Palaeontology 47, 72543.

Jacob, J., Paris, F., Monod, O., Miller, M.A., Tang, P., George, S.C. & Beny, J.-M. 2007. New insights into the chemical composition of chitinozoans. Organic Geochemistry 38, 1782-8.

Keeling, P.J., Burger, G., Durnford, D.G. et al. 2005. The tree of eukaryotes. Trends in Ecology and Evolution 20, 670-6.

Paris, F. & Nolvak, J. 1999. Biological interpretation and palaeobiodiversity of a cryptic fossil group: the "chitinozoan animal". Geobios 32, 315-24.

Servais, T., Lehnert, O., Li, J., Mullins, G.L., Munnecke, A., N├╝tzel, A. & Vecoli, M. 2008. The Ordovician biodiversification: revolution in the oceanic trophic realm. Lethaia 41, 99-110.

Tyszka, J. 2006. Morphospace of foraminiferal shells: results from the moving reference model. Lethaia 39, 1-12.

Vecoli, M., Lehnert, O. & Servais, T. 2005. The role of marine microphytoplankton in the Ordovician biodiversification event. Notebooks on Geology, Memoir 2005/2, 69-70.

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