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Topic: Metazoan


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  Cambrian Explosion
This page describes the metazoan (animal) evolutionary phenomenon popularly known as the "Cambrian explosion." The apparent discrepancy between divergence ages implied by genetic calibration techniques and a literal interpretation of the fossil record is discussed.
Thus, as far as anybody could be sure, the shelly fossil record was a literal record of metazoan evolution, and it seemed to be telling us that in the late Early Cambrian animals diversified explosively from almost nothing to approximately the full range of basic archetypes known today, in as little as 10 million years.
Bengtson, Stefan; Zhao, Yue 1997: Fossilized Metazoan Embryos from the Earliest Cambrian.
www.peripatus.gen.nz /paleontology/CamExp.html   (2892 words)

  
 Molecular Evidence for Deep Precambrian Divergences Among Metazoan Phyla -- Wray et al. 274 (5287): 568 -- Science   (Site not responding. Last check: 2007-09-19)
Our approach to estimating divergence times between metazoan phyla is based on the tendency for nucleotide and amino acid sequences to diverge over time (17-19).
Some proponents of a Cambrian explosion have suggested that the metazoan phyla diverged in as little as 8 My (4, 6), which would require sequence divergence rates in Cambrian and post-Cambrian times to differ by at least 65-fold.
Although there are substantial difficulties in resolving metazoan relationships with the use of molecular data (16), the fact that it is possible to recover even crude phylogenies from sequence data should raise suspicions about the possibility of divergences compressed into as little as 8 My.
www.sciencemag.org /cgi/content/full/274/5287/568?ijkey=4Gb.zrAEYeyQM   (5549 words)

  
 American Zoologist: Metazoan relationships on the basis of 18S rRNA sequences: A few years later...
When re-assessing three case studies, part of their conclusions was confirmed on the basis of the present 18S rRNA data set: 1) the monophyly of Arthropoda; 2) the monophyly of the Vestimentifera-Pogonophora and their protostome character; 3) the doubt about the monophyletic origin of Echiura-Sipuncula and 4) the coelomate character of Nemertea.
Despite several decades of morphological and anatomical research, numerous aspects of metazoan relationships have remained uncertain (for an overview see Brusca and Brusca, 1990; Willmer, 1990; Meglitsch and Schram, 1991).
Nearly all metazoan phyla are now represented and for some phyla tens of species have been studied (e.g., Arthropoda, Mollusca, Annelida, Nematoda; for an overview of sequences available see Van de Peer et al., 1998).
www.findarticles.com /p/articles/mi_qa3746/is_199812/ai_n8824743   (1210 words)

  
 Metazoan Parasite Infracommunities in Five Sciaenids from the Central Peruvian Coast
High values of prevalence and mean abundance of infection are associated to the polyonchoinean monogeneans; the low values of J' reinforce the strong dominance of this group in the studied communities.
The structure of the metazoan parasite community of fish, like that of other vertebrates and invertebrates, has recently attracted some attention.
The first definition of a parasitic community was given by Cloutman (1975) who said that it is "the complex of individuals belonging to the different parasite species inhabiting a host".
memorias.ioc.fiocruz.br /932/3273.html   (370 words)

  
 Metazoan book search page
Fish Diseases and Disorders : Protozoan and Metazoan Infections
Metazoan Parasite Fauna of Grebes (Aves : Podicipediformes) and Its Relationship to the Birds (Miscellaneous Publications, No 188)
excuse it, as Metazoan might by the theory that the sensational element
book-to.20m.com /metazoan.html   (106 words)

  
 WHY DID METAZOAN REEFS DISAPPEAR FOR FORTY MILLION YEARS IN THE EARLY PALEOZOIC?: BIOLOGICAL VS. PHYSICOCHEMICAL ...   (Site not responding. Last check: 2007-09-19)
Metazoans, especially archaeocyaths, were actively involved in reef building during the Early Cambrian.
The previously proposed explanations for this long post-Early Cambrian disappearance of metazoan reefs are biological in nature: no metazoan groups were available to evolve into reef-building niches, or an absence of grazers allowed calcimicrobes to flourish, or critical photosymbiotic relationships took a long time to re-evolve.
The hiatus in metazoan reefs coincides with the highest inferred level of atmospheric carbon dioxide in the Phanerozoic, and presumably attendant super-greenhouse conditions.
gsa.confex.com /gsa/2002AM/finalprogram/abstract_37778.htm   (436 words)

  
 Slushball Earth   (Site not responding. Last check: 2007-09-19)
In trying to reconstruct the origin and radiation of metazoans over the past forty years, biologists have relied mostly on analogy and homology with the anatomy, functional ecology, and development of living animals.
Anatomical and genetic evidence alike separates the earliest metazoans into three clades that represent the ancestors of sponges, cnidarians, and bilaterian metazoans, with ctenophores as the likely sister group of bilaterians.
Evidence from the development of metazoan embryos suggests strongly that all the earliest metazoans were "micrometazoans" that would have looked like the larval stages of today's simple metazoans, and quite unlike the adult stages of their modern descendants (see summary by Peterson and Davidson 2000).
www.geology.ucdavis.edu /~cowen/HistoryofLife/slushball.html   (4569 words)

  
 Metazoan deep phylogenies — can the Cambrian explosion be resolved with molecular markers?   (Site not responding. Last check: 2007-09-19)
In order to test this alternative hypothesis we (and other working groups) started a comprehensive multi-gene sequence analysis in order to contribute to the solution of this outstanding evolutionary phenomenon in metazoan evolution.
We tested and estimated some different genes which can possibly be of use to reconstruct metazoan deep phylogeny.
Mitochondrial DNA in metazoan is circular with different gene arrangements and different reading directions of the same gene locus and evolve ten times faster then nucleus DNA.
www.iscb.org /ismb2004/posters/FritzschATizbi.uni-leipzig.de_738.html   (324 words)

  
 The Cambrian exposion - Controversies   (Site not responding. Last check: 2007-09-19)
However opinion is divided upon whether this event was a true radiation of metazoan forms from a single Precambrian ancestor, or if it was simply a revolution in biomineralisation by already established phyla; an explosion of fossils rather than phyla.
There is a sudden dramatic increase in metazoan fossils at the base of the Cambrian.
It is also clear that a morphological radiation of body forms and size does not have to be the same as a taxonomic radiation of phyla.
palaeo.gly.bris.ac.uk /Palaeofiles/Cambrian/controversies/controversies.html   (429 words)

  
 Integrative and Comparative Biology: Origin of the metazoan immune system: Identification of the molecules and their ...
It is concluded that the successful evolutionary transition to the Metazoa, with the sponges as the oldest still extant phylum, and the subsequent rapid radiation into the other metazoan phyla, became possible because of the acquisition of modular molecules, involved in cell adhesion and the immune system.
Research activity focused on the elucidation of the cellular and molecular basis of immunity in sponges (phylum Porifera) was hampered by the fact that the phylogenetic position of these animals was uncertain.
This grouping is supported by the fact that the extracellular matrix molecules, as well as their corresponding cell surface receptors (Muller, 1997), had been the prerequisites for the evolution of an efficient immune system in Metazoa (Muller et al., 1999a).
www.findarticles.com /p/articles/mi_qa4054/is_200304/ai_n9170398   (1247 words)

  
 Metazoan Parasites: Black ich, flukes, and lice in slatwater aqu   (Site not responding. Last check: 2007-09-19)
Metazoan Parasites: Black ich, flukes, and lice in slatwater aqu
The past few articles have described some of the more common diseases and sicknesses that are found in aquariums.
There are three major types of metazoan parasites that I will discuss: tubellarian worms (fl ich), fish flukes, and lice.
www.suite101.com /articles/article.cfm/1815   (525 words)

  
 AEPA - Metazoan Phylogeny   (Site not responding. Last check: 2007-09-19)
Jenner, R. Metazoan phylogeny as a tool in evolutionary biology: current problems and discrepancies in application.
Jenner, R. Evolution of animal body plans: the role of metazoan phylogeny at the interface between pattern and process.
Deconstructing metazoan life cycles: larvae, adults, and cladistic character coding.
www.science.uva.nl /onderzoek/cepa/animalphyl.htm   (484 words)

  
 Literature Review: Metazoan Origins
Despite a number of recent molecular studies and a rich fossil record of sponges and cnidarians, the evolutionary relationships of the early branching metazoan groups to each other and to a putative outgroup, the choanoflagellates, remain uncertain.
To alleviate the effect of these analytical factors in the phylogenetic reconstruction of early branching metazoan lineages, we cloned multiple protein-coding genes from two choanoflagellates and diverse sponges, cnidarians, and a ctenophore.
We demonstrate that variable rates of evolution among lineages, sensitivity of the analyses to taxon selection, and conflicts in the phylogenetic signal contained in different amino acid sequences obscure the phylogenetic associations among the early branching Metazoa.
www.iscid.org /boards/ubb-get_topic-f-18-t-000008.html   (315 words)

  
 ImmInst.org -> Hydra - Immortal Metazoan life form
Senescence, a deteriorative process that increases the probability of death of an organism with increasing chronological age, has been found in all metazoans where careful studies have been carried out.
Researchers have suggested that hydra is capable of escaping aging by constantly renewing the tissues of its body.
This suggests that hydra seems to escape aging, a process known to affect all other metazoans.
www.imminst.org /forum/index.php?act=ST&f=48&t=884&s=   (829 words)

  
 Evolving ``Metazoan'' Development
The ``metazoan'' was called Ontosilica gastrulans since its development, during which three tissue layers are formed, resembles a gastrulation process.
Artificial evolution using a trivial fitness criterion resulted in a metastable sequence of epoches, each characterised by a predominant type of development.
The evolved ``metazoans'' successively include in their developmental programs cell polarity, cell-cell communication, cell movement, positional information and genetic redundancy.
staff.science.uva.nl /~roel/metazoan   (355 words)

  
 Palaeos Ecology : Radiations : Cambrian Explosion   (Site not responding. Last check: 2007-09-19)
Because several instances of this type of preservation have now been found, it may be that metazoan embryos are not uncommon as fossils but have simply been overlooked because of their minute size and nondescript morphology.
On the other hand, the metazoans must have evolved to the point where the explosion was possible.
Bengtson, Stefan and Y Zhao (1997), Fossilized metazoan embryos from the earliest Cambrian.
www.palaeos.com /Ecology/Radiations/CambrianExplosion.html   (4187 words)

  
 Animals   (Site not responding. Last check: 2007-09-19)
Origin of the metazoan phyla: Molecular clocks confirm paleontological estimates.
Molecular evidence that the myxozoan protists are metazoans.
Zrzavy, J. The interrelationships of metazoan parasites: a review of phylum- and higher-level hypotheses from recent morphological and molecular phylogenetic analyses.
tolweb.org /tree?group=Animals&contgroup=Eukaryotes   (1309 words)

  
 MIT Department of Biology: David P. Bartel   (Site not responding. Last check: 2007-09-19)
This work is uncovering a widespread influence of microRNAs on metazoan gene expression and numerous specific cases in which microRNAs are playing crucial roles during plant and animal development.
Learning the types of reactions that RNA can catalyze, how easy it is for new ribozymes to emerge, and other intrinsic properties of RNA provides a backdrop for understanding biocatalysis and is important for evaluating current notions of life’s origins and early evolution.
However, most metazoan miRNAs lack extensive complementarity to mRNAs, implying that more sophisticated computational and experimental methods are required to identify and validate most metazoan targets.
web.mit.edu /biology/www/facultyareas/facresearch/bartel.shtml   (1334 words)

  
 Column: Vendian-Cambrian
The period from around the Vendian age Varanger-Marinoan Glaciation and the, now famous, Cambrian age ‘Burgess Shale-type’ lagerstätten is pivotal to understanding the fossil record, and to the broader interpretation of metazoan evolution.
In the space of 100 million years – probably less – metazoan fossils make their first unqualified appearance and diversify to occupy a morphospace equalling if not exceeding that of today.
Microfossils, including possible bilaterian metazoan embryos, are reported from the 570 Ma Doushantuo Phosphate deposit.
www.peripatus.gen.nz /paleontology/columnVC.html   (323 words)

  
 The Cambrian explosion - timing of metazoan origins   (Site not responding. Last check: 2007-09-19)
Recently two different techniques have been used to investigate the timing of the metazoan radiation, and have independently placed the cladogenesis of the metazoan phyla back within the Precambrian, possibly even as far back as 1.2 billion years.
However the molecular clock technique has been criticised, on the invalidity of applying divergence rates from vertebrate species to comparisons between chordates and other species, and because the 'clock' carries significant margins of error.
Both of these studies add to the growing evidence for metazoan life occuring further back in the Precambrian than previosly thought.
palaeo.gly.bris.ac.uk /Palaeofiles/Cambrian/controversies/timetable/timetable.html   (342 words)

  
 [Frontiers in Bioscience 4, d805-815, December1, 1999]   (Site not responding. Last check: 2007-09-19)
Metazoan ORC is essential for initiation of replication
However, understanding the specifics of replication in metazoan organisms can only be achieved by directly addressing these questions in animal cells.
This review deals with the current state of knowledge on the metazoan Origin Recognition Complex, its composition and regulation in higher eukaryotes, its role in the initiation of replication and beyond replication, and its possible connection with human pathology.
www.bioscience.org /1999/v4/d/quintana/list.htm   (194 words)

  
 essential role   (Site not responding. Last check: 2007-09-19)
Previously, using morphological methods, it was difficult to relate "minor" animal groups representing microscopic metazoans to larger, more well known groups such as arthropods, molluscs annelids.
From molecular studies, it appears that acanthocephalans evolved from rotifers, that priapulids share common ancestry with all other molting animals (Ecdysozoa), and that flatworms, gnathostomulids and rotifers form a sister group to the remaining non-molting protostomes (Lophotrochozoa), both taxa together named Spiralia.
These findings present a very different view of metazoan evolution, and clearly show that small and simple animals do not necessarily represent ancestral or primitive taxa.
chuma.cas.usf.edu /~garey/essential.html   (190 words)

  
 Phylogenetic Invariants for Metazoan Mitochondrial Genome Evolution - Sankoff, Blanchette (ResearchIndex)   (Site not responding. Last check: 2007-09-19)
Phylogenetic Invariants for Metazoan Mitochondrial Genome Evolution (1998)
Abstract: The method of phylogenetic invariants was developed to apply to aligned sequence data generated, according to a stochastic substitution model, for N species related through an unknown phylogenetic tree.
Phylogenetic invariants for metazoan mitochondrial genome evolution, 22--31.
citeseer.ist.psu.edu /415130.html   (515 words)

  
 The Protozoan-Metazoan Boundary
Recent fossil discoveries, such as metazoan embryos and sponge spicules from rocks of Proterozoic age, as well as improvements in geochronological dating, have helped us make significant strides in Proterozoic biostratigraphy, and are shedding light on the true course of early animal evolution (see Bengston below).
Most speakers will address to what extent they believe it possible to marry the late appearance of metazoans as fossils with recent research in molecular phylogeny and zoology, which invariably imply earlier beginnings.
Metazoan evolution and the snowball earth: new perspectives on the Cambrian explosion
shum.huji.ac.il /~por/icz_xviii/protozoa.html   (408 words)

  
 Alonso Cordoba, Zoology PhD Sstudent
Traditional hypoteses for metazoan phylogeny have been based on morphological and developmental characters as well as on life history data.
The first molecular marker used to infer metazoan phylogeny was the rDNA 18S gene (SSU), and some others have been used to test the initial hypotheses, with the result of reaching certain consensus, although some clades proposed by molecular phylogenies remain controversial.
Major clades have been proposed by molecular phylogenies and are being acepted by a large portion of the scientific community, but relationships within some clades still remain unclear.
mypage.siu.edu /ajcg   (248 words)

  
 Did homeodomain proteins duplicate before the origin of angiosperms, fungi, and metazoa? -- Bharathan et al. 94 (25): ...
N terminal of the homeodomain in the angiosperm and metazoan proteins.
For instance, the metazoan HOM/Hox group is clustered in the genome
Interestingly, early metazoan development involves interactions between proteins of the two groups identified here.
www.pnas.org /cgi/content/full/94/25/13749   (2897 words)

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