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Topic: Acritarchs

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Chitinozoa

Palynology

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Central nervous system

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Dinoflagellate

	Acritarch - Wikipedia, the free encyclopedia
		Acritarchs include the remains of several quite different kinds of organisms including bacteria and dinoflagellates.
		The nature of the creatures associated with older acritarchs is generally not clear, though many are probably related to unicellular marine algae.
		Acritarchs are known from 1400Ma and had achieved considerable diversity by 1300Ma.
	en.wikipedia.org /wiki/Acritarchs (234 words)

	Ordovician acritarchs from northwestern Argentina
		In this new scenario, diversified acritarch assemblages from the Cordillera Oriental correspond to the platform facies of the foreland basin.
		Identification of the Ordovician–Silurian boundary on the basis of acritarchs is complicated because of the extinction caused by the Hirnantian glaciation.
		Acritarchs from both formations are middle Arenig in age and independently dated by conodonts from the upper part of the Oepikodus evae Zone (Rubinstein and Astini, 2000; Rubinstein 2001a, 2001b and unpublished data).
	www.unt.edu.ar /fcsnat/INSUGEO/geologia_17/19.htm (2133 words)

	Acritarchs from peri
		Acritarch investigations from the Tremadocian–"Stage 2" interval in the Eastern Cordillera of Argentina indicate that some typical forms of the messaoudensis–trifidum acritarch assemblage, including the genus Coryphidium, are present in strata related to the A.
		The taxa belong to an acritarch "province" that extends around the southern border of Gondwana, from Argentina in the east to southern China in the west.
		Acritarch microfloral succession from the Late Cambrian and Ordovician (early Tremadoc) of Random Island, eastern Newfoundland, and its comparison to coeval microfloras, particularly those of the East European Platform.
	www.unt.edu.ar /fcsnat/INSUGEO/geologia_17/14.htm (1585 words)

	Acritarchs and Chitinozoa
		From Devonian times onwards the abundance of acritarchs appears to have declined, whether this is a reflection of their true abundance or the volume of scientific research is difficult to tell.
		Acritarchs are extremely valuable for stratigraphic correlation of rocks of Proterozoic and Palaeozic age, primarily because they are the only microfossils commonly preserved.
		Acritarch morphology forms the basis of their classification therefore it is worth describing in some detail.
	www.ucl.ac.uk /GeolSci/micropal/acritarch.html (1873 words)

	Fossil Record of the Dinoflagellata (Site not responding. Last check: 2007-10-19)
		Spherical organic-walled microfossils known as acritarchs, some of which may be dinoflagellate hystrichospheres, first appear in rocks about 1.8 billion years old.
		However, acritarchs lack a characteristic dinoflagellate feature, the archaeopyle or excystment pore through which the dinoflagellate exits the cyst; they also lack the cingulum groove characteristic of many dinoflagellates.
		Exactly what the acritarchs were is not known with certainty; they probably included a number of clades of eukaryotic algae, and are thus a "form taxon," including all those spore-like fossils which have not been conclusively assigned to another group.
	www.ucmp.berkeley.edu /protista/dinoflagfr.html (364 words)

	Nat' Academies Press, Tempo and Mode in Evolution: Genetics and Paleontology 50 Years After Simpson (1995) (Site not responding. Last check: 2007-10-19)
		Acritarchs increase in both total and assemblage diversity in 900-to 800-Ma-old rocks (Figures 1–3), due largely to the differentiation of ornamented forms.
		Given the population genetic possibilities of such changes, it is surprising that the greater increase in acritarch diversity and tempo is concentrated at the beginning of the Cambrian Period.
		Of course, the sharp increase in acritarch diversity and turnover coincides with a comparable evolutionary burst in animals.
	books.nap.edu /books/0309051916/html/63.html (6314 words)

	Interpreting Late Precambrian Microfossils -- Zhang et al. 282 (5395): 1783 -- Science
		Acritarchs and diagenetic structures in the Doushantuo phosphorites (microscopic photographs on the thin sections) for comparison with the "parenchymella larvae" described by Li et al.
		Acritarch specimen of Ericiasphaera magna (Zhang) preserved in the Doushantuo phosphorite from Wengan, South China.
		acritarchs and the flagella of the parenchymella larvae.
	www.sciencemag.org /cgi/content/full/282/5395/1783a (2093 words)

	[No title]
		Acritarch vesicle, process and flange morphology, together with vesicle wall ultrastructure and excystment mechanism can be used to cluster forms with similar morphological characteristics that may be of greater practical value in palaeoenvironmental interpretation.
		Dinoflagellates, hystrichospheres and the classification of the acritarchs.
		Acritarchs could aggregate by chance during sample processing, by faecal pelletization, or could have formed within a sporangia-like structure, although such structures are considered unlikely for D. laevigata.
	www.nhm.ac.uk /hosted_sites/tms/tms-pg-abstracts.doc (1784 words)

	Definition: Palynology
		But at a more practical level, palynology is defined by the broad methodology by which its subject material is prepared for study: digestion of clastic materials with various acids to yield an organic residue amenable to microscopic scrutiny.
		Acritarchs are organic-walled, acid-resistant micorfossils of uncertain biological affinities that are classified on the basis of their morphology.
		Acritarchs are widely distributed in sedimentary rocks from the Proterozoic and Phanerozoic.
	www.peripatus.gen.nz /Paleontology/defPalynology.html (874 words)

	ABNORMAL ACRITARCHS: A TERATOLOGICAL CASE FROM THE LLANDOVERY/WENLOCK BOUNDARY IN THE AMAZON BASIN, NORTHERN BRAZIL (Site not responding. Last check: 2007-10-19)
		The documentation of abnormal acritarchs is still relatively poor in the palynological literature.
		Cramer, in 1968, was the first to mention a possible case of acritarch malformation in Veryhachium europaeum from the Silurian Maplewood Shale of New York, although he did not assign any chronostratigraphic or paleoecological significance to it.
		Furthermore, he suggests that the noticeable occurrence of abnormal acritarchs near the Llandovery/Wenlock boundary could be related to such global phenomena as widespread volcanic activity, paleomagnetic inversions, or the impact of extraterrestrial bolides.
	gsa.confex.com /gsa/2002AM/finalprogram/abstract_44698.htm (396 words)

	Cryogenian - Wikipedia, the free encyclopedia
		The tillite deposits occur also in places which were at low latitudes during the Cryogenian, which lead to the hypothesis of Snowball Earth.
		The population of acritarchs crashed during this glaciation and it is claimed that oxygen levels in the atmosphere increased after the glaciation.
		There are a number of enigmatic features about this glaciation, including indications of glaciation at very low latitudes and the presence of limestones -- sediments which are normally warm water above and below and intermixed with glacial deposits.
	www.wikipedia.org /wiki/Varanger_glaciation (416 words)

	REED WICANDER'S PAGE
		Acritarchs are marine, microscopic algae of unknown affinity that were abundant during the Proterozoic through Paleozoic eras (670 - 245 million years ago).
		Acritarchs are also excellent guide fossils, that is, because of their world-wide distribution and short geologic ranges, they can be used to age-date and correlate rock formations, which is important in working out the geologic history of an area.
		Lastly, acritarchs are important because they are the organisms from which Paleozoic oils are derived.
	www.cst.cmich.edu /units/gel/FACPAGES/erw.htm (1294 words)

	[No title] (Site not responding. Last check: 2007-10-19)
		They are age-diagnostic for the Skiagia-Fimbriaglomerella acritarch Zone, time-equivalent to the Schmidtiellus mickwitzi trilobite Zone (the lower part of the formation), and the Heliosphaeridium-Skiagia acritarch Zone corresponding to the Holmia kjerulfi trilobite Zone (the upper part of the formation).
		Acritarchs and cyanobacteria are primary producers and constitute the basic link in the food web of marine ecosystem, and thus provide a first insight into the detection of biotic response to changing environments and initial change in the trophic chain.
		Acritarch news Malgorzata Moczydlowska: Acritarchs are gaining more attention, because of their biostratigraphic significance, in the debate about the Series/Stage subdivision of the Cambrian System, carried out by the Working Group of the International Subcommission on Cambrian Stratigraphy, IUGS (Geyer & Shergold, 2000; Episodes, 23 (3),188-195).
	www.shef.ac.uk /~cidmdp/ac16.doc (5364 words)

	Theses from Uppsala University : 5726 - Cambro-Ordovician microorganisms: acritarchs and endoliths
		New assemblages of Cambrian-Ordovician acritarchs from Kolguev Island, Arctic Russia and Middle Cambrian ichnofossils of endoliths from Peary Land, North Greenland are studied.
		Twenty-seven acritarch species are described in detail and 10 taxa are left under open nomenclature.
		The studied acritarch assemblages are taxonomically rich and age-diagnostic and used to recognise Upper Cambrian and Tremadoc strata on Kolguev Island.
	publications.uu.se /theses/abstract.xsql?isbn=91-506-1798-2 (500 words)

	Silurian phytoplankton of the type Ludlow area
		The stratigraphical range of acritarchs is Precambrian (1.4 By, rare until 0.9 By)–Recent, although they are most commonly recovered from Palaeozoic strata.
		Most acritarchs are probably algal (?phytoplanktonic) cysts (Martin 1993, Colbath and Grenfell 1995) and recent molecular studies (the identification of triaromatic dinosteroids in Precambrian–Triassic rocks) have indicated that some acritarchs may be dinoflagellates, or the phylogenetic precursors of dinoflagellates (Moldowan
		Acritarch and prasinophyte algal taxa are listed alphabetically herein, a scheme that has general acceptance over artificial classifications (e.g.
	www.le.ac.uk /geology/glm2/acritarchs.html (525 words)

	k17 Acritarchs (Site not responding. Last check: 2007-10-19)
		Acritarchs are more or less spherical microfossils (with diameters greater than the less than 10 micron diameter of modern procaryotes).
		However, prior to the time of Hadrynian glacials, a flurry of diversitfication is recored for acritarchs in wide variety of sediments.
		As such, some of their species, round or radiate, and variously ornamented with spines, ridges, papillae (Figure k17i), have the potential to be guide fossils for the earliest part of Hadrynian strata.
	geowords.com /histbooknetscape/k17.htm (280 words)

	SEARCH SILO Locator [SUBJECT Acritarchs]
		Acritarch biostratigraphy of the Lower Cambrian and the Precambrian-Cambrian boundary in southeastern Poland / Author: Moczydowska, Magorazta.
		Acritarchs from the Upper Proterozoic and Lower Cambrian of East Greenland / Author: Vidal Caruana, Gonzalo.
		Dinoflagellate cysts and acritarchs from the basal Kimmeridgian (Upper Jurassic) of England, Scotland and France.
	z3950.silo.lib.ia.us /cgi-bin/search.CGI?SILO&index_0=SUBJECT/STRUCTURE:PHRASE/TRUNC:RIGHT/POSITION:0&term_0=Acritarchs&start=1&records=25&elemname=B (628 words)

	Journal of Paleontology: Acritarchs and microfossils from the Mesoproterozoic Bandemall Group, Northwestern Australia
		In peritidal environments, benthic prokaryotic filaments and spheroids of matting habit and small size were permineralized by early diagenetic silicification of stromatolitic carbonates.
		benthic filaments of large size and nonmatting habit and planktonic sphaeromorph acritarchs with thin walls and moderate dimensions were compressed in mildly kerogenous shale.
		In deeper subtidal environments, planktonic megasphaeromorph acritarchs with thick walls were initially entombed in concretionary nodules in highly kerogenous shale and then permineralized by silica during later diagenesis.
	www.findarticles.com /p/articles/mi_qa3790/is_199909/ai_n8860540 (1110 words)

	SILURIAN ACRITARCHS FROM THE AMAZON BASIN, NORTHERN BRAZIL (Site not responding. Last check: 2007-10-19)
		Their vertical distribution in every stratigraphic section was charted, and their geological age assessed in terms of the previous chitinozoan-based datings established by Y. Grahn and J.H.G. Melo in 1990.
		The main acritarchs from the lower Manacapuru Formation includes Baltisphaeridium pilar, B. cariniosum, Multiplicisphaeridium saharicum, M. scaber, Domasia rochesterensis, Dateriocradus monterrosae, Neoveryhachium carminae and Perforela perforata.
		Acritarch assemblages from the Trombetas Group show close similarity to coeval assemblages from the United States, Canada, Argentina, Spain, the British Isles, Norway, Sweden (Gotland), Belgium, Poland, Turkey, Libya, and Saudi Arabia.
	gsa.confex.com /gsa/2002AM/finalprogram/abstract_45094.htm (358 words)

	Science News Online (11/7/98): Arctic fossils record evolutionary burst
		Though the researchers cannot unequivocally identify what the original organisms were, the diversity of the acritarchs is startling, says Butterfield, who discussed the discovery in the November Geology and in Toronto last week at a meeting of the Geological Society of America.
		Butterfield and Rainbird propose that some of the new acritarchs closely resemble modern eukaryotes called dinoflagellates, which account for much of the photosynthesis in the oceans and thus provide food for larger creatures.
		Regardless of the acritarchs’ affinities, however, the number and complexity of species found on Victoria Island indicate that eukaryotes were passing through a critical evolutionary period at that time, says Butterfield.
	www.sciencenews.org /sn_arc98/11_7_98/fob5.htm (552 words)

	Acritarch (Site not responding. Last check: 2007-10-19)
		La mayoría de los acritarchs son restos de solo celled seguramente lifeforms.
		Acritarchs incluye el restos de varias clases absolutamente diversas de organismos incluyendo bacterias y dinoflagellates.
		Acritarchs se conoce de 1400Ma y había logrado diversidad considerable por 1300Ma.
	www.yotor.net /wiki/es/ac/Acritarch.htm (256 words)

	Palaeobotany at Weston Observatory - Boston College (Site not responding. Last check: 2007-10-19)
		We are particularly interested in the fossil evidence surrounding the origin of terrestrial plants, the bulk of this evidence comes from the study of cryptospores, spore-like palynomorphs that pre-date the occurrence of macroscopic land plants.
		Research projects involve cryptospores, acritarchs, spores and pollen, and early land plant problematica, such as the Nematophytales.
		The composite acritarch + dinoflagellate curve, which is representative of the evolution of the phytoplankton, shows a substantially different basic pattern.
	www.bc.edu /research/westonobservatory/paleo (1651 words)

	Untitled Document
		Originally acritarchs were called hystrichosphaerids which means tiny spheres.
		Generally, acritarchs, scolecodonts, and chitinozoans continue to be the defining palynological remains in the Silurian.
		Acritarchs continue to be abundant in marine sediments and allow for the zonation of the Silurian.
	www-class.unl.edu /geol846/geopal.html (2057 words)

	Catherine Duggan (Site not responding. Last check: 2007-10-19)
		The acritarchs (extinct unicellular algae) are abundant in marine rocks of the late Precambrian to Devonian age, rare in the Carboniferous and Permian, but are then common throughout the Mesozoic and early Tertiary.
		Vitrinite reflectance and acritarch colour determinations are being made in TCD using existing digital photomicrographic and image analysis equipment funded by the Petroleum Infrastructure Programme.
		Once the variation in acritarch colour has been calibrated against vitrinite reflectance for the Devonian samples, the method will be used to assess the maturity of ca thirty samples from selected Irish offshore sections.
	www.tcd.ie /Geology/Staff/gclayton/Pal2cd.html (365 words)

	Litosfera/2002
		Acritarchs of the Lasnamägi and Uhaku Regional Stages in the South-eastern Baltic region
		The stratigraphical subdivision and lithology of the boreholes studied and palynological sampling levels are shown in Figs 2, 3.
		The acritarchs stratigraphically most valuable for the definition and correlation of Lasnamägi rocks are Pterospermopsis tranvikensis, Micrhystridium nanodigitatum, Excultibrachium concinnum, Orthosphaeridium densiverrucosum, Polygonium tenuispinosum and Veryhachium domasioides.
	www.geo.lt /Litosfera/n6A/n6A_2.htm (334 words)

	Fossil Gallery: Acritarchs (Site not responding. Last check: 2007-10-19)
		Acritarchs are spherical microfossils that look very much like the resting stage cysts of dinoflagellates and other algae.
		Some have spines; some are completely bare; but all lack some of the characteristic features of dinoflagellate cysts.
		Acritarchs first appeared in the fossil record in the Precambrian about 1.8 billion years ago, and they are still around today.
	www.paleoportal.org /fossil_gallery/taxon.php?taxon_id=96 (100 words)

	MIDDLE AND LATE CAMBRIAN ACRITARCHS FROM THE INNER CLASTIC BELT OF LAURENTIA (Site not responding. Last check: 2007-10-19)
		Acritarchs from the Middle Cambrian Conasauga Group are a close match to a basinal assemblage from the Burgess Shale (Kevin Gostlin, University of Toronto).
		Given that these tiny spiny acritarchs are distributed over such a wide range of depositional settings, perhaps they represent a general trend for the Middle Cambrian within Laurentia, rather than simply marking variation between depositional settings.
		These observations support claims by European workers have proposed that some Middle Cambrian acritarch species are widely distributed between continental blocks.
	gsa.confex.com /gsa/2005NE/finalprogram/abstract_82800.htm (383 words)

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