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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 400 (1999), S. 13-13 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SirIn his review of Steven Conn's book Museums and American Intellectual Life, 1876-1926, Thomas Gieryn asserts that long ago “museums ceased to be centres of intellectual work” (Nature 399, 31–32; 1999). ...
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 173 (1982), S. 203-223 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The development of the skull of Dermophis mexicanus (Caeciliidae) is described and compared to that of other caecilians. The chondrocranium is well developed in embryos of 25 mm total length (TL); ossification begins in the quadrate and the articular element of the lower jaw at about 30 mm TL. The occipital arch then ossifies, followed by the dorsal and lateral dermal bones, then the ventral endochondral and dermal elements. The stapes ossifies at 55 mm TL. The amount of skull roofing increases during ontogeny, although the anterior rims of the nasal capsules, the anterior part of the mesethmoid, and the hyoid apparatus remain cartilaginous throughout life. Dermophis mexicanus lacks many primary embryonic ossification centers reported by Marcus et al. ('35) for Hypogeophis; presence of these ossification centers has been presumed to be indicative of a primitive skull morphology derived with little modification from archaic amphibians (“stegocephalians”). The fetal skull is highly kinetic, and some kinesis is retained in adults. We suggest that fetal skull kinesis and early ossification of jaw suspension elements are functionally related to the intraoviducal feeding mode of this viviparous species. Based on this evidence, together with the observed ossification pattern and bone homologies, we conclude that stegokrotaphy (complete skull roofing) in caecilians is a derived condition, correlated with fossoriality, and does not indicate a direct relationship of caecilians to any known early amphibian taxon.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 190 (1986), S. 191-200 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Species of the salamander genus Plethodon have a characteristically uniform morphology. Morphological conservatism at the level of interspecific comparisons, however, is not always reflected within species. Perhaps the most extreme example of intraspecific variation is the recent description of extensive variability in limb-skeletal patterning both within and between populations of the widespread species P. cinereus. We utilized limb regeneration following experimental amputation as a tool (1) to examine whether naturally occurring variant skeletal patterns result from limb loss and regeneration in nature, and (2) to assay the intrinsic (i.e., genetic) component of between-individual variation in mesopodial patterning. We observed the following. First, regenerate patterns are strikingly different from native patterns: interelement fusions in regenerates are typically between proximodistally adjacent cartilages, whereas interelement fusions in native variant limbs occur exclusively between laterally adjacent cartilages. Fusions also are over ten times more frequent in regenerates than in native limbs. Second, there is no strong correlation between native limb pattern (typical vs. variant) and the regenerate pattern. We conclude that variability in field-collected P. cinereus reflects extensive intrapopulation variation in limb-skeletal patterning during original limb development, rather than regeneration in nature, and that limb regeneration analysis provides no evidence of a strong genetic component to between-individual variation. Finally, unusual mesopodial patterns produced during limb regeneration may be related to the mechanical factors impinging on the regenerating limb in this terrestrial species.
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  • 4
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In anuran amphibians, cranial bones typically first form at metamorphosis when they rapidly invest or replace the cartilaginous larval skull. We describe early development of the first three bones to form in the Oriental fire-bellied toad, Bombina orientalis - the parasphenoid, the frontoparietal, and the exoccipital - based on examination of serial sections. Each of these bones is fully differentiated by Gosner stage 31 (hindlimb in paddle stage) during premetamorphosis. This is at least six Gosner developmental stages before they are first visible in whole-mount preparations at the beginning of prometamorphosis. Thus, developmental events that precede and mediate the initial differentiation of these cranial osteogenic sites occur very early in metamorphosis - a period generally considered to lack significant morphological change. Subsequent development of these centers at later stages primarily reflects cell proliferation and calcified matrix deposition, possibly in response to increased circulating levels of thyroid hormone which are characteristic of later metamorphic stages. Interspecific differences in the timing of cranial ossification may reflect one or both of these phases of bone development. These results may qualify the use of whole-mount preparations for inferring the sequence and absolute timing of cranial ossification in amphibians.
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  • 5
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Direct development in amphibians is an evolutionarily derived life-history mode that involves the loss of the free-living, aquatic larval stage. We examined embryos of the direct-developing anuran Eleutherodactylus coqui (Leptodactylidae) to evaluate how the biphasic pattern of cranial ontogeny of metamorphosing species has been modified in the evolution of direct development in this lineage. We employed whole-mount immunohistochemistry using a monoclonal antibody against the extracellular matrix component Type II collagen, which allows visualization of the morphology of cartilages earlier and more effectively than traditional histological procedures; these latter procedures were also used where appropriate. This represents the first time that initial chondrogenic stages of cranial development of any vertebrate have been depicted in whole-mounts.Many cranial cartilages typical of larval anurans, e.g., suprarostrals, cornua trabeculae, never form in Eleutherodactylus coqui. Consequently, many regions of the skull assume an adult, or postmetamorphic, morphology from the inception of their development. Other components, e.g., the lower jaw, jaw suspensorium, and the hyobranchial skeleton, initially assume a mid-metamorphic configuration, which is subsequently remodeled before hatching. Thirteen of the adult complement of 17 bones form in the embryo, beginning with two bones of the jaw and jaw suspensorium, the angulosplenial and squamosal. Precocious ossification of these and other jaw elements is an evolutionarily derived feature not found in metamorphosing anurans, but shared with some direct-developing caecilians. Thus, in Eleutherodactylus cranial development involves both recapitulation and repatterning of the ancestral metamorphic ontogeny. These modifications, however, are not associated with any fundamental change in adult morphology and cannot at this time be causally linked to the evolutionary success of this extraordinarily speciose genus.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 214 (1992), S. 1-41 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Postembryonic skeletal development of the pipid frog Xenopus laevis is described from cleared-and-stained whole-mount specimens and sectioned material representing Nieuwkoop and Faber developmental Stages 46-65, plus postmetamorphic individuals up to 6 months old. An assessment of variation of skeletogenesis within a single population of larvae and comparison with earlier studies revealed that the timing, but not the sequence, of skeletal development in X. laevis is more variable than previously reported and poorly correlated with the development of external morphology. Examination of chondrocranial development indicates that the rostral cartilages of X. laevis are homologous with the suprarostral cartilages of non-pipoid anurans, and suggests that the peculiar chondrocranium of this taxon is derived from a more generalized pattern typical of non-pipoid frogs. Derived features of skeletal development not previously reported for X. laevis include (1) bipartite formation of the palatoquadrate; (2) precocious formation of the adult mandible; (3) origin of the angulosplenial from two centers of ossification; (4) complete erosion of the orbital cartilage during the later stages of metamorphosis; (5) development of the sphenethmoid as a membrane, rather than an endochondral bone; and (6) a pattern of timing of ossification that more closely coincides with that of the pelobatid frog Spea than that recorded for neobatrachian species. © 1992 Wiley-Liss, Inc.
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  • 7
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Relative size and arrangement of the brain and paired sense organs are examined in three species of Thorius, a genus of minute, terrestrial salamanders that are among the smallest extant tailed tetrapods. Analogous measurements of representative species of three related genera of larger tropical (Pseudoeurycea, Chiropterotriton) and temperate (Plethodon) salamanders are used to identify changes in gross morphology of the brain and sense organs that have accompanied the evolution of decreased head size in Thorius and their relation to associated changes in skull morphology.In adult Thorius, relative size (area measured in frontal plane, and length) of the eyes, otic capsules, and brain each is greater than in adults of all of the larger genera; relative size of the nasal capsules is unchanged or slightly smaller. Interspecific scaling phenomena-negative allometry of otic capsule, eye and brain size, isometry or slight positive allometry of nasal capsule size, all with respect to skull length-also are characteristic of intraspecific (ontogenetic) comparisons in both T. narisovalis and Pseudoeurycea goebeli.Predominance of the brain and eyes in Thorius results in greater contact and overlap among these structures and the nasal capsules in the anterior portion of the head. This is associated with anterior displacement of both the eyes and nasal capsules, which now protrude anterior to the skull proper; a change in eye shape; and medial deformation of anterior braincase walls. Posteriorly, predominance of the otic capsules has effected a reorientation of the jaw suspensorium to a fully vertical position that is correlated with the novel presence of a posteriorly directed squamosal process and shift in origin of the quadropectoralis muscle.Many of these changes in cranical morphology may be explained simply as results of mechanical (physical) interactions among the skeletal, nervous, and sensory components during head development at reduced size. This provides further evidence of the role of nervous, sensory, and other “soft” tissues in cranial skeletal morphogenesis, and reinforces the need to consider these tissues in analyses of skull evolution.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 182 (1984), S. 245-255 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The sequence of appearance of the 17 different skull bones in the oriental fire-bellied toad, Bombina orientalis, is described. Data are based primarily on samples of ten or 11 laboratory-reared specimens of each of 11 Gosner developmental stages (36-46) representing middle through late metamorphosis. Ossification commences as early as stage 37 (hind limb with all five toes distinct), but the full complement of adult bones is not attained until stage 46 (metamorphosis complete). Number of bones present at intermediate stages is poorly correlated with external morphology. As many as four Gosner developmental stages elapse before a given bone is present in all specimens following the stage at which it may first appear. The modal ossification sequence is frontoparietal, exoccipital, parasphenoid, septomaxilla, premaxilla, vomer, nasal, maxilla, angulosplenial, dentary, squamosal, quadratojugal, pterygoid, prootic, interfrontal, sphenethmoid, and mentomeckelian. Most specimens are consistent with this sequence, despite the poor correlation between cranial ossification and external development as assayed by Gosner stage.The timing of cranial ossification in Bombina orientalis differs in many respects from that described for two other, distantly related anurans, the leopard frog (Rana pipiens) and the western toad (Bufo boreas). These include the total number and sequence of appearance of bones, and the timing of ossification relative to the development of external morphology. Interspecific variation may reflect differences in the timing of the tissue interactions known to underlie skeletal differentiation and evolution.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 174 (1982), S. 57-77 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Patterns of growth and variation of the appendicular skeleton were examined in Thorius, a speciose genus of minute terrestrial plethodontid salamanders from southern Mexico. Observations were based primarily on ontogenetic series of each of five species that collectively span the range of adult body size in the genus; samples of adults of each of seven additional species provided supplemental estimates of the full range of variation of limb skeletal morphology.Limbs are generally reduced, i.e., pedomorphic, in both overall size and development, and they are characterized by a pattern of extreme variation in the composition of the limb skeleton, especially mesopodial elements, both within and between species. Fifteen different combinations of fused carpal or tarsal elements are variably present in the genus, producing at least 18 different overall carpal or tarsal arrangements, many of which occur in no other plethodontid genus. As many as four carpal or tarsal arrangements were observed in single population samples of each of several; five tarsal arrangements were observed in one population of T. minutissimus. Left-right asymmetry of mesopodial arrangement in a given specimen is also common.In contrast, several unique, nonpedomorphic features of the limb skeleton, including ossification of the typically cartilaginous adult mesopodial elements and ontogenetic increase in the degree of ossification of long bones, are characteristic of all species and distinguish Thorius from most related genera. They form part of a mechanism of determinate skeletal growth that restricts skeletal growth after sexual maturity. Interspecific differences in the timing of the processes of appendicular skeletal maturation relative to body size are well correlated with interspecific differences in mean adult size and size at sexual maturity, suggesting that shifts in the timing of skeletal maturation provide a mechanism of achieving adult size differentiation among species.Processes of skeletal maturation that confer determinate skeletal growth in Thorius are analogous to those typical of most amniotes - both groups exhibit ontogenetic reduction and eventual disappearance of the complex of stratified layers of proliferating and maturing cartilage in long bone epiphyses - but, unlike most amniotes, Thorius lacks secondary ossification centers. Thus, the presence of secondary ossification centers cannot be used as a criterion for establishing determinate skeletal growth in all vertebrates.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 205 (1990), S. 77-84 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Comparison of mesopodial skeletal patterns found in native and regenerated limbs of the salamander Plethodon cinereus reveals variant patterns unique to each group. Variant patterns in native limbs are based on fusions between laterally adjacent elements (i.e., in the anteroposterior axis). Variant patterns in the mesopodia of regenerated limbs usually exhibit fusions among proximodistally adjacent elements. Analysis of regenerates derived from limb amputation at different levels shows that the axis of fusion between regenerated mesopodial elements remains the same (i.e., proximodistal) independent of amputation level. However, the frequency of specific fusion combinations is unexpectedly sensitive to amputation level. Proximal (stylopodial) amputation results in mesopodial patterns with predominantly preaxial fusion combinations; distal amputation produces mesopodial patterns with predominantly postaxial fusion combinations. This finding is discussed in the context of other recent studies in which amputation level influenced limb regeneration patterning.
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