Dinoflagellates

24 July, 2009

 

In my micropaleontological studies in the 1980’s I dealt with peridinioid dinoflagellates, as a morphologically defined group, from the Upper Cretaceous (Maastrichtian) of Trelleborg at the southwestern part of Scania (Skåne), southern Sweden. My intention was to contribute to the taxonomy of this group by describing the forms present, recording their dimensions, and analysing the relations in shape between endocyst and pericyst.

Fossil dinoflagellates that appear morphologically related to modern Peridinium and Protoperidinium were treated as peridinioid dinoflagellate cysts. Several types, styles, and shape variants of archeopyles were recognized in this group.

In peridiniacean genera as a rule the archeopyle corresponds to the second anterior intercalary paraplate (2a) and the inferred paratabulation is of the hexastyle.

Genera which reveal indications of a quadrastyle paratabulation or have intercalary archeopyles corresponding to more than one paraplate (e.g. Trithyrodinium) or combination archeopyles corresponding to paraplates of different series (e.g. Palaeoperidinium) were not included in the peridiniacean genera, but regarded as peridinioid.

In papers on dinoflagellates detailed recordings of dimensions of the material studied and calculations on those data were rarely presented. Before 1980 I found only three studies that used morphometry:

  • Regression analysis was used to study the relation between horns and cyst body
  • The distribution of length/width ratio was used to study the interspecific variation and taxonomy of Alterbia
  • Dimensions of length, width, and length of horns and spines were graphically presented in one paper

I have treated ten species of acid resistant peridinioid dinoflagellates of Deflandrea, Isabelidinium, Palaeoperidinium, Phelodinium, Subtilisphaera, Svalbardella, and Trithyrodinium from this Upper Cretaceous (Maastrichtian) material from southern Sweden.

Taxonomical conclusions

  • The discrimination between Isabelidinium Lentin & Williams (1977) and Eurydinium Stover & Evitt (1978) according to the diagnoses, by means of length/width ratio of the endocyst is not justified in my studies. This ratio displays a normal distribution which includes values which originally have been considered critical for the discrimination of two separate genera.
  • The features discriminating Isabelidinium Lentin & Williams (1977) and Chatangiella Vozzhennikova (1967) are not clearly indicated in the original descriptions. Most of the diagnostic differences may be modifications due to environmentally controlled factors. In preserved material those morphologic features seem to display ranges which include both genera. I have published the new combination Isabelidinium armatum (Cookson & Eisenack) Lindgren.
  • Lejeunia kozlowskii Górka (1963) is a cornucavate cyst referable to Phelodinium Stover & Evitt and different from Lejeunecysta tricuspis (Wetzel) Artzner & Dörhöfer (1978). I have published the new combination Phelodinium kozlowskii (Górka) Lindgren.
  • Palaeocystodinium Alberti (1961) is a later synonym of Svalbardella Manum (1960). So is Cystodiniopsis Vozzhennikova (1963) which name however is illegitimate; the designation of a new type species is contrary to the ICBN.
  • Ceratiopsis Vozzhennikova (1967) and Pentagonum Vozzhennikova (1967) as names of dinoflagellate genera are illegitimate and must be rejected, as they are later homonyms of Ceratiopsis De Wildeman (1896) and Pentagonium Schauer (1843), which were validly published for a genus of fungi and an asclepiadacean genus, respectively.

References

Lindgren, S., 1984.
Acid resistant peridinioid dinoflagellates from the Maastrichtian of Trelleborg, southern Sweden. (Summary in Russian.) Stockholm Contrib. Geol., 39(6): 145—201. Stockholm. ISSN 0585-3532. ISBN 91-22-00519-6. — Buy at the lowest prices among books in Sweden.
Lindgren, S., 1985.
Nomenclatural notes on fossil peridinioid dinoflagellates. Taxon, 34 (4): 670—671. Utrecht. ISSN 0040-0262.

Web Links

Dinoflagellates; by Matthew Olney, University College, London.

Dinoflagellates; by Mona Hoppenrath and Juan F. Saldarriaga, Forschungsinstitut Senckenberg, Germany, and University of British Columbia, Canada

Introduction to the Dinoflagellata; by Graham Williams & Andrew MacRae, Museum of Paleontology, University of California, Berkeley.

Peridinium; by Charles J. O’Kelly, Protist Image Database.

Graham Williams, Dartmouth, 1996

Charles Downie, Sheffield, 1923—1999

Bill Sarjeant, Saskatoon, 1935—2002; also in The Encyclopedia of Saskatchewan.

Lewis Stover, Kerrville, 1925—1993

Tamara Vozzhennikova, Novosibirsk, 1914—2000

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Morphometry of peridinioid dinoflagellates

24 July, 2009

In peridinioid dinoflagellates of the Maastrichtian (Upper Cretaceous) of Trelleborg (Scania, southern Sweden) analyses of the length/width ratio of the pericysts and the endocysts of different species also indicate that the variation of the pericysts generally is greater than that of the endocysts. The endocysts display a less elongated shape which is fairly constant within a species. The specific mean values of the length/width ratio of endocysts range between 0.8 and 1.4 with the median value = 1.0, while the specific mean values for the pericysts range from 1.3 to 4.5, with the median value = 2.1

In these peridinioid dinoflagellates the restricted variation in size and shape of the endocysts indicates that the endophragm was developed under strong genetic control inside the motile, vegetative theca. The pericysts, however, display a wide morphologic variation which may be the result of influences by environmentally controlled factors during the development of the periphragm. This development may have taken place also on the outer side of the motile theca, or even after its decay.

Analyses of the Trelleborg material of the length/width ratio of pericysts and endocysts by reduced major axis in scatter diagrams indicate that within a genus the slopes of the regression lines are close to each other within a genus with statistically significant correlation coefficients. Thus the slope of the regression lines may be used for taxonomical purposes.

See also >> Dinoflagellater: mätningar och klassifikation (in Swedish only)


Leiospheres

24 July, 2009
 
Leiosphere is a common name without taxonomic implications for thin-walled smooth or slightly ornamented spherical microalgae. The botanical affinities of leiospheres are unknown.Simple, thin-walled spheres, like Leiosphaeridia, may develop in a variety of algal taxa. When found as fossil remains, these spheres may appear morphologically undistinguishable, despite they are naturally unrelated.
Many acid resistant spherical microfossils have been recorded in sediments ranging from the early pre-Cambrian to Recent. They are widespread in pre-Cambrian and Paleozoic deposits.

 

The taxonomic classification is hazardous and complex in this group where the only features for classification are wall structure, ornamentation, and opening mechanisms. These features are not sufficient for a classification to modern algal taxa above the rank of species—not even at the rank of class.

The importance assigned to morphological characters for classification at the rank of genus or species appears merely to be a question of personal opinion. For modern algae neither shape or ornamentation, nor apertures are relevant taxonomic characters at the rank of genus.

Leiospheres have generally been considered as resting cysts and their aperture (pylome) has been interpreted as an excystment opening. However, they may also represent vegetative stages of the algal life cycle. There may be no possibility of discriminating between vegetative and resting stages (cysts) in fossil material.

 

 

 

    FORWARD TO


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

 

 

Web Links

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

Halosphaera, a small planktonic flagellate and a large planktonic cyst; by Charles J. O’Kelly, Protist Image Database

Introduction to the Micromonadophyceae; from University of California, Berkeley.

Non-Marine Palynomorphs from the Middle Cambrian Bright Angel Shale, Grand Canyon USA. Paul K. Strother, Weston Observatory, Boston College.

Terrestrial Organic Remains from Lower Paleozoic Paralic Sequences. Paleobotany Laboratory at Weston Observatory. In Research Projects.

Palynology at the Hole. Rob Fensome and Andrew MacRae, Canadian Association of Palynologists.

 

 

 


Morphology and taxonomy of Leiospheres

24 July, 2009

 

Many acid resistant spherical microfossils have been recorded in sediments ranging from the early pre-Cambrian to Recent.

Leiosphere is a common name without taxonomic implications for thin-walled smooth or slightly ornamented spherical microalgae. The botanical affinities of leiospheres are unknown.

Simple, thin-walled spheres, like Leiosphaeridia, may develop in a variety of algal taxa. When found as fossil remains, these spheres may appear morphologically undistinguishable, despite they are naturally unrelated.

No features used for classification of modern algae—even at the rank of class—are preserved in fossil leiospheres. 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.

Above the rank of genus leiospheres have been placed in morphologic groupings that are outside the sequence of ranks of taxa treated under the International Code of Botanical Nomenclature. They are not determined by means of nomenclatural types and not based upon priority of publication. Thus, all such groupings are equally applicable. The name acritarch meaning “of uncertain origin” was used by Evitt in 1963.

As morphologic groupings above the rank of genus in a completely artificial scheme of classification do not reflect any natural or genetical relations, the genera may better be arranged and discussed simply in alphabetical order. This may be particularly relevant because the algal cell may display a variability of shape during the life cycle.

The taxonomic classification is hazardous and complex in this group where the only features for classification are wall structure, ornamentation, and opening mechanisms. These features are not sufficient for a classification to modern algal taxa above the rank of species—not even at the rank of class.

Ornamentation is the main taxonomic character in several genera in this complex group, and has been used also as a diagnostic character at the rank of genus. However, in classification of modern algae it is relevant only at the rank of species. Even size has been used in some taxa as the only character of diagnostic value.

The importance assigned to morphological characters for classification at the rank of genus or species appears merely to be a question of personal opinion. For modern algae neither shape or ornamentation, nor apertures are relevant taxonomic characters at the rank of genus.

The wide size range from 8 µm to 440 µm in Leiosphaeridia indicates that different natural groups are included in the genus, but in comparison with modern algae it does not exclude definitely, however, that it is a natural genus.

In the leiospheres there are many badly defined and partly superfluous taxa. Several species are synonymous because they have been assigned to different genera which are synonymous. Species overlap because of different interpretations of ranges of diagnostic characters among investigators. Inadequate illustrations and insufficient diagnoses have made identification difficult. Accidental and diagenetic features have been interpreted as taxonomically valid.

However, some forms of leiospheres are morphologically well defined and have a restricted variability, at least in the same stage of the life cycle. They are distinct form species, no matter the name and circumscription of the genus to which they may belong. These forms are considered useful for biostratigraphic correlations and age determinations, specially in the pre-Cambrian and lower Palaeozoic.

    FORWARD TO


Botanical affinities
Diagnostic features in modern algae
Morphometry of modern and fossil algae
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.
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.

 

Web Link

Are the green algae (phylum Viridiplantae) two billion years old? by Bernard Teyssèdre, Paris. Notebooks on Geology, Article 2006/03 (CG2006_A03), September 19, 2006


Botanical affinities of Leiospheres

24 July, 2009

 

Leiospheres have generally been considered as resting cysts and their aperture (pylome) has been interpreted as an excystment opening. However, they may also represent vegetative stages of the algal life cycle, as in modern acid resistant microalgae apertures similar to pylomes may develop also in vegetative stages, e.g. as flagellar pores.

There may be no possibility of discriminating between vegetative and resting stages (cysts) in fossil material. The acid resistance and the possibility to be fossilized are widespread in the algae and occur variably in all their life stages, in vegetative cells and also in resting cysts.

 

Apertures

Apertures have a restricted taxonomic significance and they are not useful for the determination of life stages. Vegetative stages of algae and also encysted resting stages are likely to be preserved as fossils. Apertures on vegetative cells, however, cannot always be definitely discriminated from excystment openings. The pylome may be a flagellar pore similar to that of certain modern algae (e.g. Trachelomonas, see below).

If the fossils are of flagellate affinity, every one should have an aperture in its vegetative stage. Forms without apertures may be cysts of the same or different species, but also vegetative stages of unflagelled taxa. When the aperture is an excystment feature, it is present only during one life stage. Cells without apertures then may be closed cysts, but also vegetative stages of other than flagellate affinity. Cells with apertures may be mature cysts, but also vegetative stages of flagellate affinity.

In the original diagnosis of Leiosphaeridia (Eisenack 1958) pylome (aperture) is said to be present. In the following original description is remarked that pylomes are common in some species but rare or absent in others. This variation is proposed to be depending either on specific characters or on the stage of the life cycle of the organisms at the time when they were buried. Microfossils with pylomes were interpreted as obviously abandoned cells in their final life stage, and the function of the opening, was without doubts considered to be making it possible for the protoplast to extrude. Consequently pylomes are not necessarily present on every fossil specimen of a taxon, and their occurrence has no taxonomic value. Only their structure may be a feature important for the classification, possibly limited to the rank of species.

In some taxa a pylome is always present, in others pylomes are never or only occasionally observed with certainty. In “thousands of specimens” of the original material of Leiosphaeridia plicata and L. ralla there was no pylome (Felix 1965), and in 3324 specimens of L. wenlockia there were “one or two” with pylome (Downie 1959).

Generally, leiospheres have been considered as cysts having pylomes and ruptures as excystment features. However, since excystment is a genetically controlled characteristic process that is constant within a taxon, pylomes and ruptures cannot exist both as excystment features in the same species.

 

Environmental modifications

In the fossil record most often it is impossible to elucidate if variability is due to environmentally controlled factors or to different stages of the algal life cycle. Thus, different fossil genera from distant deposits may be only modifications of the same natural species.

Cells that do not differentiate hard parts do not always obtain identical morphological features when they are developed separately in different environments. Except this environmentally controlled morphogenesis the different life stages of the algal cell may generate morphologic variability. Further, in restricted environments disastrous events may occur which may often generate radical changes in the metabolism and morphological appearance of the cells.

A satisfactory classification of modern algae must pay sufficient attention to the morphological variability and life history of each taxon. Many species first described on the basis of specimens representing only one stage of their life cycles were later defined as life stages of other species.

 

Coenobia

I have identified fossil algal coenobia in a sample from the Upper Riphean Mirojedikha Beds in the Turukhansk region, eastern Siberia. The fossils I investigated derive from the Mirojedikha River and were extracted from a sample from the Upper Riphean Mirojedikha Beds.

The Mirojedikha Beds are about 200 m thick shallow water sediments consisting of dolostones, limestones, and shales. The present sample was collected in l967 by my friend, the Late Professor Boris V. Timofeev at the type locality at the Mirojedikha River, four kilometers from its confluence with the Yenisey River, 30 kilometers north of the town of Turukhansk. The sample is a dark-grey, clayey shale which derives from the lower part of the Mirojedikha Beds.

Vesicles of coenobia and solitary leiospheres do not display morphologic differences. The dimensions of vesicles of coenobia correspond to those of larger specimens in the bimodal size distribution of solitary leiospheres from the same sample.

Algal coenobia are sparsely reported as fossil findings. From the Cretaceous-Tertiary they are described as the genus Palambages. The first findings of coenobia in the Palaeozoic were reported from the Silurian of Libya in 1962. There were not any records from the Precambrian until my findings in 1982.

Faulty or rough processing may be the reason for the scantiness of reports of fossil colonies. Maybe most samples yield colonies rather than single specimens if they are treated with gentle care. Clusters, flakes, and different kinds of agglomerations of uniform fossil microalgae have been reported as colonies though they do not strictly represent colonies.

A coenobium is a definitely integrated colony composed of a certain number of cells which are determined during its early development; after the embryonic phase cell-division does not occur until the following reproductive phase. In coenobia the joints and sheaths are usually resistant and likely to be preserved as fossils. However, unicell production and colony formation are influenced by environmentaly controlled factors.

In the algae there is a parallel development from simple to more elaborate forms so that practically all types of cellular and colonial organizations have their counterparts in different classes. The characters necessary for discrimination between classes are not preserved as fossils. Consequently, relating fossil coenobia to modern algal taxa is impossible.

I referred both coenobial and solitary forms to a species with the new combination name Leiosphaeridia asperata (Naumova) Lindgren. Kildinella hyperboreica is not the correct name of this taxon. Protoleiosphaeridium, Kildinella, and Polyedrosphaeridium are congeneric with Leiosphaeridia, as well as the not validly published genera Leiopsophosphaera, Macroptycha, and Scaphita.

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Morphology and taxonomy
  FORWARD TO


Diagnostic features in modern algae
Morphometry of modern and fossil algae
Genus Leiosphaeridia
Distribution of Leiosphaeridia

References

Downie, C., 1959.
Hystrichospheresfrom the Silurian Wenlock Shale of England. Paleontology, 2: 26—71. London.
Eisenack, A., 1958.
Tasmanites Newton 1875 und Leiosphaeridia n.g. als Gattungen der Hystrichosphaeridea. Palaeontographica Abt.A, 110: 1—19. Stuttgart.
Felix, C.J., 1965.
Neogene Tasmanites and leiosphere from southern Louisiana, U.S.A Palaeontology, 8: 16—26. 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., 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.


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