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  • 1
    Publication Date: 2015-10-01
    Description: A well-known characteristic of chondrichthyans (e.g. sharks, rays) is their covering of external skin denticles (placoid scales), but less well understood is the wide morphological diversity that these skin denticles can show. Some of the more unusual of these are the tooth-like structures associated with the elongate cartilaginous rostrum ‘saw’ in three chondrichthyan groups: Pristiophoridae (sawsharks; Selachii), Pristidae (sawfish; Batoidea) and the fossil Sclerorhynchoidea (Batoidea). Comparative topographic and developmental studies of the ‘saw-teeth’ were undertaken in adults and embryos of these groups, by means of three-dimensional-rendered volumes from X-ray computed tomography. This provided data on development and relative arrangement in embryos, with regenerative replacement in adults. Saw-teeth are morphologically similar on the rostra of the Pristiophoridae and the Sclerorhynchoidea, with the same replacement modes, despite the lack of a close phylogenetic relationship. In both, tooth-like structures develop under the skin of the embryos, aligned with the rostrum surface, before rotating into lateral position and then attaching through a pedicel to the rostrum cartilage. As well, saw-teeth are replaced and added to as space becomes available. By contrast, saw-teeth in Pristidae insert into sockets in the rostrum cartilage, growing continuously and are not replaced. Despite superficial similarity to oral tooth developmental organization, saw-tooth spatial initiation arrangement is associated with rostrum growth. Replacement is space-dependent and more comparable to that of dermal skin denticles. We suggest these saw-teeth represent modified dermal denticles and lack the ‘many-for-one’ replacement characteristic of elasmobranch oral dentitions.
    Keywords: evolution, palaeontology, developmental biology
    Electronic ISSN: 2054-5703
    Topics: Natural Sciences in General
    Published by Royal Society
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  • 2
    Publication Date: 2003-02-22
    Description: Placoderms are extinct jawed fishes of the class Placodermi and are basal among jawed vertebrates. It is generally thought that teeth are absent in placoderms and that the phylogenetic origin of teeth occurred after the evolution of jaws. However, we now report the presence of tooth rows in more derived placoderms, the arthrodires. New teeth are composed of gnathostome-type dentine and develop at specific locations. Hence, it appears that these placoderm teeth develop and are regulated as in other jawed vertebrates. Because tooth development occurs only in derived forms of placoderms, we suggest that teeth evolved at least twice, through a mechanism of convergent evolution.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, Moya Meredith -- Johanson, Zerina -- New York, N.Y. -- Science. 2003 Feb 21;299(5610):1235-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Craniofacial Development, Dental Institute, King's College London, Guy's Campus, London Bridge, London SE1 9RT, UK. moya.smith@kcl.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12595693" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biological Evolution ; Dentition ; Fishes/*anatomy & histology ; *Fossils ; *Paleodontology ; Phylogeny ; *Tooth ; Western Australia
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 1991-01-18
    Description: Two vertebrates from the Colorado Formation are known to have acellular bone and dentine, tissues found in heterostracan fishes and proposed as the primitive exoskeleton. High-resolution optical microscopy and scanning electron microscopy indicate that a third vertebrate is represented by a quite distinct exoskeleton of denticles, with many cell and cell process spaces throughout, tissue that resembles that of osteostracans more than heterostracans. Cellular bone coexists with cellular dentine in this Ordovician vertebrate, demonstrating that these skeletal tissues are as old as acellular bone. Both are proposed to come from neural crest because denticles are considered homologous with teeth.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, M M -- New York, N.Y. -- Science. 1991 Jan 18;251(4991):301-3.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17733288" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 1990-02-16
    Description: The nucleosome is the fundamental unit of assembly of the chromosome and reversible modifications of the histones have been suggested to be important in many aspects of nucleosome function. The structure-function relations of the amino-terminal domain of yeast histone H4 were examined by the creation of directed point mutations. The four lysines subject to reversible acetylation were essential for histone function as the substitution of arginine or asparagine at these four positions was lethal. No single lysine residue was completely essential since arginine substitutions at each position were viable, although several of these mutants were slower in completing DNA replication. The simultaneous substitution of glutamine for the four lysine residues was viable but conferred several phenotypes including mating sterility, slow progression through the G2/M period of the division cycle, and temperature-sensitive growth, as well as a prolonged period of DNA replication. These results provide genetic proof for the roles of the H4 amino-terminal domain lysines in gene expression, replication, and nuclear division.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Megee, P C -- Morgan, B A -- Mittman, B A -- Smith, M M -- GM28920/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 1990 Feb 16;247(4944):841-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Microbiology, School of Medicine, University of Virginia, Charlottesville 22908.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2106160" target="_blank"〉PubMed〈/a〉
    Keywords: Acetylation ; Alleles ; Cell Cycle ; Chromosome Deletion ; Codon/genetics ; Glutamine ; Histones/*genetics/metabolism ; *Lysine ; Mutation ; Plasmids ; Protein Processing, Post-Translational ; Saccharomyces cerevisiae/cytology/*genetics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 1992-05-29
    Description: From histological investigations into the microstructure of conodont elements, a number of tissue types characteristic of the phosphatic skeleton of vertebrates have been identified. These include cellular bone, two forms of hypermineralized enamel homologs, and globular calcified cartilage. The presence of cellular bone in conodont elements provides unequivocal evidence for their vertebrate affinities. Furthermore, the identification of vertebrate hard tissues in the oral elements of conodonts extends the earliest occurrence of vertebrate hard tissues back by around 40 million years, from the Middle Ordovician (475 million years ago) to the Late Cambrian (515 million years ago).〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sansom, I J -- Smith, M P -- Armstrong, H A -- Smith, M M -- New York, N.Y. -- Science. 1992 May 29;256(5061):1308-11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geological Sciences, University of Durham, United Kingdom.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1598573" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Bone and Bones/*ultrastructure ; Cartilage/*ultrastructure ; *Fossils ; Microscopy, Electron, Scanning ; Paleontology ; Phylogeny ; Vertebrates/*anatomy & histology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2019
    Description: Abstract The dissipation of wave energy in the marginal ice zone is often attributed to wave scattering and the dissipative mechanisms associated with the ice layer. In this study we present observations indicating that turbulence generated by the differential velocity between the sea ice cover and the orbital wave motion may be an important dissipative mechanism of wave energy. Through field measurements of under‐ice turbulence dissipation rates in pancake and frazil ice, it is shown that turbulence‐induced wave attenuation coefficients are in agreement with observed wave attenuation in the marginal ice zone. The results suggest that the turbulence‐induced attenuation rates can be parameterized by the characteristic wave properties and a coefficient. The coefficient is determined by the ice layer properties.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 1985-01-01
    Print ISSN: 1527-1404
    Electronic ISSN: 1938-3681
    Topics: Geosciences
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 91 (1986), S. 1-10 
    ISSN: 1432-1424
    Keywords: synthesis ; assembly ; transmembrane protein ; multisubunit ; receptor ; ion channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 396 (1998), S. 729-730 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The ‘spine-brush complex’ of the extinct, mid-Palaeozoic primitive chondrichthyan shark Stethacanthus is one of the strangest vertebrate appendages known. Its structure has never been defined, but here we reveal that the ‘brush’ is actually an enlarged, specialized ...
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Planta 136 (1977), S. 65-70 
    ISSN: 1432-2048
    Keywords: Callose ; Temperature stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seedlings of Zea mays L., Sorghum vulgare, Pisum sativum L., Phaseolus aureus, Glycine max L. and Lycopersicum esculentum were grown at 20°C and at 26°C. The seedlings were fixed in glutaraldehyde and sections were examined for aniline-blue-induced fluorescence, which is supposedly indicative of β-1,3-glucans or callose. There was much more aniline-blue fluorescence in Zea, Glycine and Phaseolus seedlings grown at 20°C compared with 26°C whereas Pisum and Lycopersicum seedlings grown at 26°C showed more fluorescence than those grown at 20°C. In Zea, large deposits of fluorescent material were particularly noticeable in the walls of elongating cells around the shoot apex and in root-cap cells, and appeared to be closely associated with a few of the pitfields. The remaining pitfields showed the normal, low level of aniline-blue fluorescence.
    Type of Medium: Electronic Resource
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