Diagnostic features in modern algae comparable to Leiosphers

24 July, 2009

 

Chlorococcales

The features considered to be of greatest taxonomic importance at the rank of genus in the modern Chlorococcales are chromatophores, pyrenoids, and zoospores. None of these are preserved in fossils. Modifications due to environmental influences cannot always be discriminated from hereditary variability by microscopic analyses alone. In preserved modern material it is impossible to extract the various stages necessary for distinguishing genera and species. That is also a major difficulty in mixed cultures of living material—and of course in fossil material. Thus, cultivation is the essential method for taxonomic classification of many unicellular modern algae.

The fossil leiospheres lack all the characters mentioned above, which are necessary for their classification in modern algal taxa—even at the rank of class. It is evidently impossible also to discriminate between different morphological appearances due to ontogenetic variability and environmental modifications. Consequently the leiospheres must be arranged in an artificial system without biological implications, but as far as possible according to biological principles.

Cysts are metabolically dormant cells with a considerably higher resistance than vegetative cells to detrimental physical conditions, other than heat. Desiccation resistance may be a survival attribute in nature, and this property seems to be related to the outer cell wall.

The size is not a sole diagnostic character. Anyhow related modern taxa (genus, species) seem to have a limited size range so measurements may be important features for determination of modern algae. I have compared the size distribution in Leiosphaeridia to vegetative stages of modern unicellular Chlorococcales.

Cyanophyceae

In the Cyanophyceae the normal reproductive cell, the akinete, is a spherical or cylindrical cell with a smooth or granulated surface. It is characterized by a considerable increase in size compared with the vegetative cell, and before maturation it will expand still more. The ultrastructure is similar to that of the vegetative cell, but with a new outer wall added. Thus the akinete can be regarded as an enlarged vegetative cell enclosed by a thick outer envelope.

Akinete-like cells with thickened walls develop also in the Chlorophyceae, but conditions associated with the production of this stage were not sufficiently investigated.

Akinete germination occurs in different ways. Frequently it generates the rupturing of the outer wall. The excystment mechanism is a true taxonomical feature. According to genetical control, some taxa will dehisce by an aperture (pylome), others by a rupture. However, this is recognizable only in certain stages of their life cycles.

 

Modern algae Trachelomonas

My laboratory investigations of the modern euglenophycean algae Trachelomonas volvocina showed that the lorica of these specimens is acid resistant and that after treatment in acids their flagellar pore is similar to the pylome of leiospheres. The living cells are spherical but they collapse during the acetolyzis process and form folds similar to those said to characterize the fossil genus Kildinella (=Leiosphaeridia).

Trachelomonas is characterized by a lorica that is often iron impregnated, with an apically located flagellar pore, and a very long flagellum. The species are discriminated by shape, ornamentation, processes, and flagellar pore features. A series of 447 illustrations (Conrad & van Meel 1952) of Trachelomonas species shows that shape, ornamentation, processes, and aperture characteristics are not significant taxonomic features at the rank of genus.

About 250 species of Trachelomonas are known. The cells show a considerable variability in size and shape, which makes the taxonomy of the group complex. This variability is also due to different stages of the life history of the organisms and to environmentally controlled morphogenesis. In acidic water some species may have a hyaline, smooth lorica, whereas the same species in alkaline water have thickened lorica impregnated with iron- and manganese-compounds. Exposed to unfavourable environmental conditions some species of Trachelomonas will develop into round, thick-walled resting cells that may be difficult to discriminate from specimens of other genera, even of different classes, e.g. the chlorophycean genus Chlamydomonas.

Specimens of Trachelomonas shown on the internet.

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Morphology and taxonomy
Botanical affinities
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Morphometry of modern and fossil algae
Genus Leiosphaeridia
Distribution of Leiosphaeridia

References

Conrad, W. & van Meel, L., 1952.
Matériaux pour une monographie de Trachelomonas Ehrenberg, C., 1834, Strombomonas Deflandre, G., 1930 et Euglena Ehrenberg, C., 1832, Genres d’Euglénacées. Mém. Inst. R. Sci. Nat. Belg., 124: 1—176, pls. 1—13.
Lindgren, S., 1981.
Remarks on the taxonomy, botanical affinities, and distribution of leiospheres. (Summary in Russian) Stockholm Contrib. Geol., 38(1): 1—20. Stockholm. ISBN 91-22-00500-5. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
Taxonomic review of Leiosphaeridia from the Mesozoic and Tertiary. Stockholm Contrib. Geol., 38 (2): 21—33. Stockholm. ISBN 91-22-00502-1. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
Algal coenobia and leiospheres from the Upper Riphean of the Turukhansk region, eastern Siberia. Stockholm Contrib. Geol., 38 (3): 35—45. Stockholm. ISBN 91-22-00504-8. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 37 (11): 139—143. Stockholm. ISBN 91-22-00487-4. ISSN 0585-3532.
Lindgren, S., 1984.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 39 (5): 139—144. Stockholm. ISBN 91-22-00517-x. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
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Morphometry of modern Chlorococcales and fossil Leiosphaeridia (algae)

24 July, 2009

 

The size is not a sole diagnostic character. Anyhow related modern taxa of the rank of genus as well as species seem to have a limited size range and measurements may be important features for determination of modern algae.

The size distribution in Leiosphaeridia may be compared to vegetative stages of modern unicellular Chlorococcales. The knowledge of size relations between vegetative cells and resting cysts is too fragmentary for comparisons.

For comparisons of dimensions among taxa a “size difference” value (SD) may be calculated as the size range value in per cent of the minimum size value (Lindgren 1981).

size


Figure 1
A. Cumulative diagram showing size differences in 49 genera of the Chlorococcales. Size difference of Leiosphaeridia is indicated by an L.
B. Cumulative diagram showing size differences in 257 species of the Chlorococcales (curve C), and in 55 species of Leiosphaeridia (curve L).
The size difference is calculated as the size range value in per cent of the minimum value. (From Stockholm Contrib. Geol., 38(1): 8, figure 1)


In 49 genera of the Chlorococcales tabulated from Philipose (1967) the size difference varies between SD = 4 and SD = 5400, with a median value of SD = 250 (fig. 1A). Only in six genera the size difference exceeds SD = 1000, and only in two it exceeds SD = 4000. Specimens of Ankistrodesmus Corda 1838 emend. Ralfs 1848 (seven species) range from 3 µm to 165 µm (SD = 5400), and specimens of Chlorococcum Fries 1820 (three species) range from 2 µm to 109 µm (SD = 5350).

In Leiosphaeridia the size range is recorded as 8—440 µm. The size difference is SD = 5400.

Thus the size difference for genus Leiosphaeridia is extremely high, but not quite impossible for a natural taxon. In described species of Leiosphaeridia, however, the size range is far more restricted than in modern Chlorococcales (fig 1B).

In 257 species of the Chlorococcales, also tabulated from Philipose (1967), the size difference in vegetative cells ranges between SD = 4 and SD = 1163, with a median value of SD = 100. 13.6 % of the difference values exceed SD = 200 and 4.7 exceed SD = 350.

In 55 species of Leiosphaeridia (including Protoleiosphaeridium) the size difference ranges from SD = 3 to SD = 203, with a median value of SD = 58.

The values of the size differences are summarized in table I

 


Table I
Size differences in modern Chlorococcales and fossil Leiosphaeridia

 

Number 

 

 

 

 

Size difference 

 

 

 

 

of taxa 

 

 

 

 

Minimum 

 

 

 

Maximum 

 

 

 

Median 

 

 

 

Mean 

 

 

 

Genera             
Chlorococcales

49

 

 

 

 

4

 

 

 

5400

 

 

 

250

 

 

 

557

 

 

 

Leiosphaeridia 

1

 

 

 

   

5400

 

 

 

   
             
Species             
Chlorococcales

257

 

 

 

 

4

 

 

 

1163

 

 

 

100

 

 

 

128

 

 

 

Leiosphaeridia 

55

 

 

 

 

3

 

 

 

203

 

 

 

58

 

 

 

62

 

 

 

 The size difference is calculated as the size range value in per cent of the minimum value.

 

 

 

 

  

 

 

 

 

  

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Morphology and taxonomy
Botanical affinities
Diagnostic features in modern algae
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Genus Leiosphaeridia
Distribution of Leiosphaeridia

References

Lindgren, S., 1981.
Remarks on the taxonomy, botanical affinities, and distribution of leiospheres. (Summary in Russian) Stockholm Contrib. Geol., 38(1): 1—20. Stockholm. ISBN 91-22-00500-5. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Philipose, M.T., 1967.
Chlorococcales. Indian Counc. Agric. Res., New Delhi. 365 p.

 

 

Web Link

Steiner, M., 1997. Chuaria circularis Walcott 1899 — “megasphaeromorph acritarch” or prokaryotic colony? Acta Universitatis Carolinae, Geologica, 40: 645—665. Prague.



Genus Leiosphaeridia

24 July, 2009

 

The taxonomic classification of spherical microalgae is very complex, since:

  • it is impossible to refer these forms to modern algal taxa because of the lack of relevant characters for classification
  • vegetative cells and resting stages (cysts) cannot be discriminated with respect to only fossilized parts;
  • cell shape and ornamentation may vary between different stages of the algal life cycle and can be modificatively affected by environmental factors, such as nutrition and temperature
  • excystment features (pylomes, ruptures) are not constant in the algal life cycle, and excystment apertures (pylomes) cannot be discriminated always with certainty from apertures in vegetative stages, e.g. flagellar pores.

Leiosphaeridia (Eisenack 1958) comprises acid resistant, spherical to ovoidal microfossils without processes, without divisions into fields, and without traverse and longitudinal furrows or girdles. The cell wall is thin and without tubes, the surface is smooth or with slight ornamentation. An aperture (pylome) may be present, and has been considered as an excystment mechanism. Other methods of dehiscence are also recorded, e.g. by a split.

The original diagnosis by Eisenack in 1958 was slightly emended by Downie and Sarjeant in 1963 to include slight ornamentation and to exclude reference to colour. However, the view on color was taken earlier, and published by Eisenack in 1962.

Leiosphaeridia was established to accommodate leiospheres not attributable to Tasmanites (Newton 1875) because the nomenclatural type of Leiosphaera—a genus introduced by Eisenack in 1938—proved to be conspecific with a species of Tasmanites.

 

Synonymy

  • Kildinella, Lophosphaeridium, and Protoleiosphaeridium do not display any differences from the diagnosis of Leiosphaeridia. Also Leiopsophosphaera and Uniporata seem to be congeneric with Leiosphaeridia.
  • Leiosphaeridium is an illegitimate name. Macroptycha and Scaphita are not validly published.
  • Campenia and Lancettopsis may be congeneric with Leiosphaeridia, but are not examined.

Kildinella (Shepeleva & Timofeev ex Timofeev) comprises according to the protologue smooth or shagreen spherical microfossils, ranging from 15 to 70 µm in diameter, with clearly delimited folds. They differed from Leiosphaeridia specimens only in being smaller and having denser membranes.

The folds evidently were generated by compression and the restricted size range is of no taxonomic value. When I examined the original material of Kildinella, I could not find any distinct features different from the diagnosis of Leiosphaeridia.

Kildinella was established by Shepeleva & Timofeev in 1963, but no species was described and no nomenclatural type was indicated. Thus the name was not validly published until Timofeev in 1966 described Kildinella hyperboreica and designated it as the type species.

Only a few species of Kildinella have been described. My friend, the Late Professor Boris V. Timofeev showed to me in Leningrad 1979 that they are essential parts of biostratigraphically useful microalgal assemblages identified in the pre-Cambrian of the Soviet Union.

Lophosphaeridium (Timofeev ex Downie) differs from Leiosphaeridia only in having a tuberculose ornamental sculpture. The difference is diffuse and a more or less developed ornamentation is the only feature for the generic classification. When I examined the original material of Lophosphaeridium, I could not find any distinct features different from the diagnosis of Leiosphaeridia. However, I regarded more extensive analyses required for establishing the taxonomic relations.

Lophosphaeridium was introduced by Timofeev in 1959 but as no type species was selected it was not valid until Downie designated the nomenclatural type in 1963.

Protoleiosphaeridium comprises small leiospheres (less than 50 µm in diameter) with smooth or shagreen surface, and ranges completely within the diagnosis of Leiosphaeridia. This genus was established by Timofeev in 1959, and became valid by designation of a lectotype in 1960. The circumscription of the genus was slightly expanded by Staplin in 1961 as to include all types of minor overall ornamentation. Leiosphaeridia and Protoleiosphaeridium were treated as congeneric by Downie & Sarjeant in 1963.

Leiopsophosphaera (Naumova) comprises large cells with smooth or shagreen, pitted surface. Dr Pykhova told me in 1978 that Leiopsophosphaera differs from Leiosphaeridia and Uniporata only in the sculptural ornamentation. This Proterozoic and Palaeozoic genus seems to range within the diagnosis of Leiosphaeridia.

A more detailed investigation of the taxonomy should indude a close examination of the original material if it is preserved. Studying that material was not possible for me, nor was I able to find Naumova’s paper from 1960 with the original diagnosis. Leiopsophosphaera and Leiosphaeridia were treated as congeneric by Yin & Li in 1978.

Uniporata (Naumova in Pykhova) comprises cells with ornamented surface and a large pylome. Dr Pykhova told me in 1978 that Uniporata differs from Leiosphaeridia only in having a large pylome. The type species indicated in the protologue of Uniporata is a nomen nudum and thus the name is not validly published.

The Proterozoic and Palaeozoic genus Uniporata was established by Naumova in Pykhova 1969. It seems to range within the diagnosis of Leiosphaeridia. A more detailed investigation of the taxonomy should indude a close examination of the original material if it is preserved. Studying that material was not possible for me.

Leiosphaeridium was proposed by Timofeev in 1959 as an amendment of Eisenack’s Leiosphaera. The original spelling of a name is to be retained and Leiosphaeridium is not to be considered an orthographic variant of Leiosphaera. As the name is nomenclaturally superfluous, it is illegitimate.

Staplin emended Timofeev’s diagnosis of Leiosphaeridium and regarded the name “as a new generic taxon” with L. eisenackii (Timofeev) as a new type species. Based on a different type the name is a later homonym and thus illegitimate.

The transference to Leiosphaeridia of Leiosphaeridium eisenackii made by Downie & Sarjeant in 1963 is not valid since it is done without clear references to the basionym.

Macroptycha and Scaphita are names used by Timofeev in 1973 for boat-shaped forms with large longitudinal folds or without folds, respectively. However, both names were not validly published. The folds were interpreted as prolonged chambers, but evidently represent compressional features. Before 1973 forms identical with Macroptycha and Scaphita were referred to Leiosphaeridia by Timofeev and others.

Campenia, described by Mädler in 1963, differs from Leiosphaeridia in possessing an elliptical slit that is supposed to be homologous with the pylome. The diagnosis of Leiosphaeridia, however, does not exclude opening by a slit. Lancettopsis—also described by Mädler in 1963—comprises folded and rolled up vesicles similar to Scaphita. Analyses of the original material is required for establishing the taxonomic relations.

 

Complex classification

To illustrate the complex leiosphere classification two species may be mentioned.

Protoleiosphaeridium papillatum was described by Staplin in 1961. Two years later—in 1963—it was transferred (but not validly) to Leiosphaeridia by Downie & Sarjeant, and further five years later—in 1968—to Lophosphaeridium by Martin.

Protoleiosphaeridium granulosum was also introduced by Staplin in 1961. It was in 1963 transferred by Downie & Sarjeant to Leiosphaeridia, and in the same year by the same Downie (without Sarjeant as coauthor) to Lophosphaeridium. Both these transferences are, however, contrary to the nomenclatural rules, and the valid publication of the name Leiosphaeridia granulosa was made by Pocock in 1972—but for a different taxon!

 

New species

I have described two new species of acid resistant spherical microalgae, referable to genus Leiosphaeridia, from the Upper Cretaceous of the province Scania (Skåne), southern Sweden.

Leiosphaeridia nelliae Lindgren 1982c is described from a Cenomanian clay deposit penetrated by a boring at Åhus in the Kristianstad area. This species is diagnosed by its small size and the lack of apertures or any obvious dehiscence mechanism. It resembles some Palaeozoic species, but all Mesozoic species with similar appearance are much larger.

Leiosphaeridia scanica Lindgren 1984 is described from the Campanian and Maastrichtian penetrated by a boring at Trelleborg. This species differs from other species of Leiosphaeridia in having a smooth vesicle and a constantly present pylome.

Leiosphaeridia asperata (Naumova) Lindgren is a new combination I established in my 1982b paper with Trachytriletus asperatus Naumova as basionym.

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Morphology and taxonomy
Botanical affinities
Diagnostic features in modern algae
Morphometry of modern and fossil algae
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Distribution of Leiosphaeridia

References

Eisenack, A., 1958.
Tasmanites Newton 1875 und Leiosphaeridia n.g. als Gattungen der Hystrichosphaeridea. Palaeontographica Abt. A, 110: 1—19. Stuttgart.
Eisenack, A., 1962.
Einigen Bemerkungen zu neueren Arbeiten uber Hystrichosphären. Neues Jb. Geol. Paläont. Mh., 102: 92—101. Stuttgart.
Downie,C. & Sarjeant, W.A.S., 1963.
On the interpretatio and status of some hystrichospher genera. Palaeontology, 6: 83—96. London.
Lindgren, S., 1981.
Remarks on the taxonomy, botanical affinities, and distribution of leiospheres. (Summary in Russian) Stockholm Contrib. Geol., 38(1): 1—20. Stockholm. ISBN 91-22-00500-5. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982a.
Taxonomic review of Leiosphaeridia from the Mesozoic and Tertiary. Stockholm Contrib. Geol., 38 (2): 21—33. Stockholm. ISBN 91-22-00502-1. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982b.
Algal coenobia and leiospheres from the Upper Riphean of the Turukhansk region, eastern Siberia. Stockholm Contrib. Geol., 38 (3): 35—45. Stockholm. ISBN 91-22-00504-8. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982c.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 37 (11): 139—143. Stockholm. ISBN 91-22-00487-4. ISSN 0585-3532.
Lindgren, S., 1984.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 39 (5): 139—144. Stockholm. ISBN 91-22-00517-x. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.


Distribution of Leiosphaeridia

24 July, 2009

 

Spherical microalgae are widespread in pre-Cambrian and Paleozoic deposits. The number of reported occurrences of Leiosphaeridia significantly decreases between the Devonian and Jurassic. Species described from the Mesozoic and Tertiary are not recorded from the Proterozoic and Palaeozoic, and vice versa.

I rewieved twentyone species of Leiosphaeridia described from post-Palaeozoic deposits. Five of them were considered as conspecific with other Leiosphaeridia-species, two were not validly published, and five were attributable to other genera.

Geographic and stratigraphic distribution of Mesozoic and Tertiary Leiosphaeridia is tabulated in my article Lindgren 1982.

Mesozoic and Tertiary Leiosphaeridia

Attributed to the genus Leiosphaeridia:

L. aptiana
L. nelliae
L. ? ovata
L. plicata
L. pusilla
L. sarjeantii
L. similis
L. trematophora
L. variabilis

Conspecific with other Leiosphaeridia-species:

L. deflandrei
L. granulosa
L. minutaespinosa
L. ralla
L. tangentensis

Not validly published:

L. caperata
L. taxodiforma

Attributable to genera other than Leiosphaeridia:

L. asymmetrica
L. eisenackii
L. ? scrobiculata
L. spongiosa
L. staplinii

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Morphology and taxonomy
Botanical affinities
Diagnostic features in modern algae
Morphometry of modern and fossil algae
Genus Leiosphaeridia
   

References

Lindgren, S., 1981.
Remarks on the taxonomy, botanical affinities, and distribution of leiospheres. (Summary in Russian) Stockholm Contrib. Geol., 38(1): 1—20. Stockholm. ISBN 91-22-00500-5. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
Taxonomic review of Leiosphaeridia from the Mesozoic and Tertiary. Stockholm Contrib. Geol., 38 (2): 21—33. Stockholm. ISBN 91-22-00502-1. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1982.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 37 (11): 139—143. Stockholm. ISBN 91-22-00487-4. ISSN 0585-3532.
Lindgren, S., 1984.
A new taxon of Leiosphaeridia (algae) from Upper Cretaceous clays, southern Sweden. Stockholm Contrib. Geol., 39 (5): 139—144. Stockholm. ISBN 91-22-00517-x. ISSN 0585-3532. — Buy at the lowest prices among books in Sweden.


Tetraporina

24 July, 2009

 

Upper Cretaceous clay deposits of the Kristianstad area in southern Sweden have yielded plant microfossils of various kinds. I studied unicellular, acid-resistant microfossils from the locality Åsen (Näsum parish) and interpreted them as vegetative cells and resting cysts of algae. I described forms referred to the genus Tetraporina Naumova.

Several modern algal taxa include forms which are similar to Tetraporina with regard to the outer shape, surface ornamentation, and cell wall build up, so I did not refer Tetraporina to any modern algal taxon.

The impossibility in referring Tetraporina to a natural algal group is further accentuated by the fact that the development of modern unicellular algae, similar to those fossil forms, includes morphological changes which at least in part are due to environmentally controlled factors, such as nutrition and temperature. Tetraporina is thus a form genus of admittedly heterogeneous composition.

I emended the generic diagnosis of Tetraporina and described ten new species: Tetraporina denticulata, T. diagonalis, T. foveolata, T. mammillata, T. pulvinula, T. scanica, T. spinifera, T. verruculosa, T. vesiculata, and T. villandica.

 

References


Lindgren, S., 1980
.
Algal microfossils of the form genus Tetraporina from Upper Cretaceous clays, southern Sweden. Review of Palaeobotany and Palynology, 30: 333—359. Amsterdam. ISSN 0034-6667.
Lindgren, S., 1987.
Modern algae resembling fossil Tetraporina. (Abstract in Hindi.) The Palaeobotanist, 35 (2): 131—135. Lucknow. ISSN 0031-0174.

Supposed Vendian plant fossils

24 July, 2009

 

In 1979 I examined the original material of pre-Cambrian vendotaenids in Leningrad for the first time, and later in 1986. The interpretation of successive floras of vendotaenids and the proposed stratigraphic significance of these taxa is discarded. The proposed affinity of vendotaenids to Phaeophyta, Rhodophyta or any algal taxon was not demonstrated at that time. Nor was the presence of reproductive structures of vendotaenids unequivocally demonstrated.

The genus Vendotaenia Gnilovskaya 1971 is not related to or synonymous with Laminarites Sternberg 1854, nor is V. antiqua Gnilovskaya 1971 synonymous with L. antiquissimus Eichwald 1854. The genera Majaphyton and Ulophyton were not examined with respect to their affinity and relation to vendotaenids. No fact supported the idea that Eoholynia is a descendant of Ulophyton.

 

References

Lindgren, S., 1987.
Paleoalgology. Contemporary research and applications. Earth-Science Reviews, 24: 289—291. Elsevier, Amsterdam. ISSN 0012-8252. ISBN 0-387-15312-8 .

 

 

The Ediacaran was officially named as a new geologic period in May 2004

 

Web Links

Pre-Ediacarian fauna from Timan. Abstract 1998, by M.B. Gnilovskaya et al., Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg

The oldest tissue differentiation in Precambrian (Vendian) algae. Abstract 2002 by M.B. Gnilovskaya, Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg

Neoproterozoic to Lower Cambrian carbonaceous mega-fossils. Project by Bernd-Dietrich Erdtmann & Michael Steiner.

Vendian cyanobacterial communities as a preservation factor of fossil eucaryotic algal remains. Abstract by M.V. Leonov

New phaeophycean fossils in the Early Cambrian from Chengjiang Biota at Ercai Village, Southwest China; abstract.


The Ediacaran period

24 July, 2009

 

The Ediacaran period was the first new official geologic time period designated after 1891. It was officially named as a new geologic period in May 2004. The Ediacaran covers the time from the last ice ages of the Cryogenian period 600 Ma (million years ago) to the beginning of the Cambrian period 543 Ma (million years ago).

 ediacaran
 

 

 

 

 

 

 

 

 

 

 

 

The geological timeline
Image sources: BBC   ICS

International ratification of the new period reflects our expanding knowledge of Earth’s deep physical and biological history. The last part of the pre-Cambrian was a special time when creatures of uncertain affinity appeared, like soft-bodied jellyfish-like animals and sea-sluggish beasts. One idea is that climate shocks at the Cryogenian—Ediacaran periods triggered the evolution of complex, multi-celled life and the appearance of the first shelled animals.

Already in 1859, Charles Darwin suspected there was something significant that preceded the Cambrian Explosion. What he did not know, however, was that few of the animals of the Ediacaran appear to have survived to the Cambrian. There were simple animals on the Ediacaran side and complex animals on the Cambrian side of the stratigraphic border.

Many of the new life forms in the Ediacaran were simple organisms, probably related to present-day sponges. They are supposed to be living flat on the seafloor and may have had photosynthetic symbionts, as corals have today. Most paleontologists agree that the Ediacaran assemblage includes early cnidariangrade animals, as well as burrows and trails, and perhaps body fossils of early bilaterians (bilateral organisms).

The Ediacaran organisms became probably extinct when the first predators came along among those new and diverse animals that evolved during the Cambrian Explosion. Then the Ediacaran period ended suddenly and the Cambrian period began.

The Ediacaran period was named after the Ediacara Hills in South Australia. The name is of Australian Aboriginal origin and refers to a place where water is present.

In accordance with international rules, the new period has been defined by an event recorded in a single section of rock outcropping termed the global stratotype section and point (GSSP). It is the reference section that defines the standard for recognition of the base of the new period worldwide. The initial GSSP of the Ediacaran period lies at the base of a texturally and chemically distinctive carbonate layer that overlaies glaciogenic rocks in an exposure along Enorama Creek in the Flinders Ranges, South Australia.

However, there was no general agreement on the decision of the name Ediacaran by the International Union of Geological Sciences (IUGS) and the International Commission on Stratigraphy (ICS).

In international geology and stratigraphy there is a long tradition to use the term Vendian, so this name is likely to be used also in the future as an alternative name.

Vendian was introduced in 1952 as name for a sedimentary rock system in the former Soviet Union by the academician Boris Sokolov at the Academy of Sciences of the USSR. Based on Chinese deposits the same period was named Upper Sinian in China.

 

 

Web Links

You say Ediacaran, I say Vendian; by Anna Salleh, ABC Science Online

Geological time gets a new period; from BBC News

Ediacaran period; from the GeoWhen database

Introduction to the Vendian period; from the University of California Museum of Paleontology