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    Wyświetlanie 1-4 z 4
    Tytuł:
    Chaetognath grasping spines from the Upper Mississippian of Arkansas [USA]
    Autorzy:
    Doguzhaeva, L A
    Mutvel, H.
    Mapes, R.H.
    Powiązania:
    https://bibliotekanauki.pl/articles/23070.pdf
    Data publikacji:
    2002
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    grasping spine
    fossil
    USA
    protoconodont
    organic spine
    phosphatized fossil
    morphology
    Arkansas
    ultrastructure
    Chaetognatha
    paleontology
    chaetognath
    Opis:
    Previously unidentified tiny (about 0.5 mm in length), hollow, gently curved, serrated spines probably originally composed of horny, organic fibers from the Upper Mississippian (Middle Chesterian = Namurian A equivalent or lower Serpukhovian) of Arkansas (USA) are described, and their probable chaetognath affinities are discussed. The specimens are preserved in an oval accumulation (about 15 mm long and 6 mm wide) of approximately 200 specimens within a small (about 25 mm in length) phosphatic concretion. For comparison, the grasping spines of the Recent chaetognath Eukrohnia hamata were examined. The Arkansas specimens are named Eoserratosagitta serrata gen. et sp. nov., and this genus is assigned to the Phylum Chaetognatha. The Upper Mississippian spines are also compared with protoconodonts. This comparison supports the hypothesis that the chaetognaths may have existed in the Cambrian.
    Źródło:
    Acta Palaeontologica Polonica; 2002, 47, 3
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Functional morphology and modifications on spine growth in the productid brachiopod Heteralosia slocomi
    Autorzy:
    Perez-Huerta, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/22228.pdf
    Data publikacji:
    2013
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    functional morphology
    modification
    spine growth
    productid brachiopod
    brachiopod
    Heteralosia slocomi
    Brachiopoda
    Productida
    tubular hollow spine
    silicification
    ontogenesis
    paleoecology
    Opis:
    Spines are one of the most characteristic ornamenting features of many fossil brachiopod taxa. Despite several studies of spines in different species, there is still insufficient information about the development, functionalmorphology, andmodifications of brachiopod spines. In particular, ontogenetic data are very rare and the understanding of the relationship between functional morphology and paleoecology is elusive. The present study analyzes the functional morphology and modifications on spines of the Pennsylvanian brachiopod species Heteralosia slocomi throughout ontogeny. Spines are tubular hollow and only displayed on the surface of the ventral valves, where they develop from a specific point at the margins of the growth lamellae and directed towards the anterolateral margins.Modifications of up to 180 from this original direction of growth are observed in response to ecological pressure and biotic interactions. The function of these spines is primarily for attachment by clasping and cementation, but the possibility of spines acting as sensory mechanisms is not excluded.
    Źródło:
    Acta Palaeontologica Polonica; 2013, 58, 2
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Morphology and histology of dorsal spines of the xenacanthid shark Orthacanthus platypternus from the Lower Permian of Texas, USA: palaeobiological and palaeoenvironmental implications
    Autorzy:
    Beck, K.G.
    Soler-Gijon, R.
    Carlucci, J.R.
    Willis, R.E.
    Powiązania:
    https://bibliotekanauki.pl/articles/21629.pdf
    Data publikacji:
    2016
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    morphology
    histology
    dorsal spine
    xenacanthid shark
    shark
    Orthacanthus platypterus
    Chondrichthyes
    Xenacanthiformes
    Lower Permian
    Texas
    USA
    paleobiology
    paleoenvironment
    Opis:
    Detailed studies on Carboniferous species of the xenacanth Orthacanthus have shown that the xenacanth dorsal fin spine can be used for skeletochronological analyses and provides valuable information about development, growth and environmental life conditions of those extinct sharks. We report here for the first time the histology and skeletochronology of Permian specimens, dorsal spines of Orthacanthus platypternus from the Craddock Bone Bed (lower Clear Fork Formation; Early Permian, Leonardian age) of northern Baylor County (north-central Texas, USA). Twelve dorsal spines of O. platypternus preserve a highly vascularized wall mainly composed of centrifugally growing dentine in a succession of dentine layers, probably deposited with an annual periodicity. As expected, spines of individuals with 1–2 dentine layers, presumably juveniles, present the smallest sizes. However, spines of individuals showing at least 3–4 dentine layers and interpreted to be subadults/young adults, are distributed in two spine-size clusters corresponding to females (probably the largest spines) and males, in agreement with the hypothesis of sexual size dimorphism proposed in a previous biometric analysis. Our comparative study of O. platypternus and the Stephanian species O. meridionalis further suggests that spine denticulation can be useful for distinguishing between species of Orthacanthus and sexually dimorphic forms (juvenile to adults) in each species. Total body length estimations of O. platypternus from the Craddock Bone Bed point to relatively large juveniles and small subadults/young adults (less than 2 m in total length), living as opportunistic predators in the pond-channel coastal plain environments represented by the bone bed deposits. The comparative analyses of the ontogenetic stages of the recorded specimens of O. platypternus and their distribution along different facies and localities indicate that this species was euryhaline, diadromous with a catadromous life-cycle which was strongly regulated by the semi-arid, seasonally dry tropical climate affecting western Pangaea during the Early Permian.
    Źródło:
    Acta Palaeontologica Polonica; 2016, 61, 1
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The integument of Cambrian chancelloriids
    Autorzy:
    Bengtson, S
    Hou, X.
    Powiązania:
    https://bibliotekanauki.pl/articles/22108.pdf
    Data publikacji:
    2001
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    Coeloscleritophora
    Allonnia
    China
    integument
    body surface
    enigmatic organism
    sclerite
    cactus spine
    chancelloriid
    Cambrian
    paleontology
    Lower Cambrian
    Chancelloriidae
    paleozoology
    Opis:
    Details of the body surface of the chancelloriid Allonnia from the Lower Cambrian Chengjiang biota in southwestern China elucidate the nature of these enigmatic organisms. Rhombically arranged elements, about 30 x 60 ym, are interpreted as representing imbricating platelets, the distal ends of which projected as spinules from the body surface. Comparisons with other chancelloriids suggest that the flexible integument was continuous with the aragonitic sclerites that sit on the surface like cactus spines, and that both were formed by an epidermal epithelium secreting a continuous exo- and endocuticle. In the sclerites, the exocuticle was mineralized; the unmineralized endocuticle and cellular extensions from the epithelium filled the interior of the sclerites. In the flexible integument the epithelium was overlain by endocuticle and unmineralized exocuticle. This structure of soft integument and sclerites is at variance with proposals of poriferan or ascidian affinity of chancelloriids but in accord with a coeloscleritophoran model.
    Źródło:
    Acta Palaeontologica Polonica; 2001, 46, 1
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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