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Endochondral Bone (endochondral + bone)

Distribution by Scientific Domains
Life Sciences40%

Terms modified by Endochondral Bone

  • endochondral bone formation
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  • endochondral bone growth
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    Selected Abstracts

    An enigmatic gnathostome vertebrate skull from the Middle Devonian of Bolivia

    ACTA ZOOLOGICA, Issue 2009
    Alan Pradel
    Abstract A new taxon, Ramirosuarezia boliviana n. gen., n. sp. is erected for a single, articulated jawed fish (gnathostome) skull from the Middle Devonian (Eifelian) Icla Formation of Bolivia. The specimen displays an elasmobranch-like braincase, but lacks unambiguous elasmobranch and even chondrichthyan characters, although its peculiar tooth-bearing ,labial' elements evoke certain stem-holocephalans. Its endoskeletal elements seem lined with either perichondral bone or non-prismatic calcified cartilage, but show no evidence of endochondral bone. Although devoid of large dermal bones and scales, R. boliviana shares with certain ,ostracoderms', placoderms and holocephalans the lack of an otico-occipital fissure, but lacks a hypophysial fenestra. Certain features (elongated braincase, ,labial elements', sharp denticles and teeth) are also suggestive of the equally enigmatic coeval stensioellids, once regarded as either primitive placoderms or stem holocephalans. The jaws are armed with platelets that bear blunt to pointed and sharp teeth, in which synchrotron radiation microtomography yields evidence of a large pulp cavity, a possibly osteichthyan-like character. No character clearly supports affinities of R. boliviana to any of the currently known major gnathostome groups. Tenuous hints suggest a relationship to the enigmatic fossil Zamponiopteron, from the Eifelian of Bolivia, known by peculiar calcified ,fin plates' and isolated shoulder girdles. [source]

    Histological structure of the cancellous bone layer in Bothriolepis canadensis (Antiarchi, Placodermi)

    LETHAIA, Issue 3 2005
    CAROLE BURROW
    The Placodermi are extinct basal gnathostomes which had extensive dermal and perichondral bone, but which lacked the endochondral bone which characterizes the more derived bony fishes. Thin sections of bone from a specimen of the antiarch placoderm Bothriolepis canadensis, from the Escuminac Formation (Frasnian, Upper Devonian), Québec, Canada, reveal that part of the cancellous layer in its dermal and endoskeletal bone formed from perichondral bone trabeculae growing around cartilage spheres. The resultant structure mimics that of osteichthyan endochondral bone. The layout and dimensions of this polygonal mosaic patterning of the bone trabeculae and flattened cartilage spheres resemble those of the prismatic layers of calcified cartilage in chondrichthyans. If the lack of endoskeletal bone in chondrichthyans is a derived character, then the structure identified in B. canadensis could represent a ,template' for the formation of prismatic calcified cartilage in the absence of bone. [source]

    Redundant function of the heparan sulfate 6-O-endosulfatases Sulf1 and Sulf2 during skeletal development

    DEVELOPMENTAL DYNAMICS, Issue 2 2008
    Andreas Ratzka
    Abstract Modification of the sulfation pattern of heparan sulfate (HS) during organ development is thought to regulate binding and signal transduction of several growth factors. The secreted sulfatases, Sulf1 and Sulf2, desulfate HS on 6-O-positions extracellularly. We show that both sulfatases are expressed in overlapping patterns during embryonic skeletal development. Analysis of compound mutants of Sulf1 and Sulf2 derived from gene trap insertions and targeted null alleles revealed subtle but distinct skeletal malformations including reduced bone length, premature vertebrae ossification and fusions of sternebrae and tail vertebrae. Molecular analysis of endochondral ossification points to a function of Sulf1 and Sulf2 in delaying the differentiation of endochondral bones. Penetrance and severity of the phenotype increased with reduced numbers of functional alleles indicating redundant functions of both sulfatases. The mild skeletal phenotype of double mutants suggests a role for extracellular modification of 6-O-sulfation in fine-tuning rather than regulating the development of skeletal structures. Developmental Dynamics 237:339,353, 2008. © 2008 Wiley-Liss, Inc. [source]

    Homology of fin lepidotrichia in osteichthyan fishes

    LETHAIA, Issue 1 2005
    ZERINA JOHANSON
    Lepidotrichia are dermal elements located at the distal margin of osteichthyan fins. In sarcopterygians and actinopterygians, the term has been used to denote the most distal bony hemisegments and also the more proximal, scale-covered segments which overlie endochondral bones of the fin. In certain sarcopterygian fishes, including the Rhizodontida, these more proximal, basal segments are very long, extending at least half the length of the fin. The basal segments have a subcircular cross section, rather than the crescentic cross section of the distal lepidotrichial hemisegments, which lack a scale cover and comprise short, generally regular, elements. In rhizodonts and other sarcopterygians, e.g. Eusthenopteron, the basal elements are the first to appear during fin development, followed by the endochondral bones and then the distal lepidotrichia. This sequence contradicts the ,clock-face model' of fin development proposed by Thorogood in which the formation of endochondral bones is followed by development of lepidotrichia. However, if elongate basal ,lepidotrichia' are not homologous with more distal, jointed lepidotrichia and if the latter form within a distal fin-fold and the former outside this fold, then Thorogood's ,clock-face' model remains valid. This interpretation might indicate that the fin-fold has been lost in early digited stem-tetrapods such as Acanthostega and Ichthyostega and elongate basal elements, but not true lepidotrichia, occur in the caudal fins of these taxa. [source]