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    Wyświetlanie 1-5 z 5
    Tytuł:
    The Burges Shale animal Oesia is not a chaetognath: A reply to Szaniawski [2005]
    Autorzy:
    Morris, S C
    Powiązania:
    https://bibliotekanauki.pl/articles/21841.pdf
    Data publikacji:
    2009
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    discussion
    paleontology
    Middle Cambrian
    Burges Shale
    Oesia disjuncta
    chaetognath
    Opis:
    The Middle Cambrian Oesia disjuncta, a monospecific genus, is known only from the celebrated Burgess Shale of British Columbia. It has been re−interpreted by Szaniawski (Acta Palaeontologica Polonica 50:1–8; 2005) as a chaetognath, a distinctive phylum whose exact position in the protostomes is still controversial. Unequivocal chaetognaths, that have no similarity to Oesia, are already known to occur in the Chengjiang Lagerstätte (Lower Cambrian, S.W. China), and here I describe the first example of a chaetognath from the Burgess Shale itself. Comparisons between Oesia and chaetognaths fail to find any significant homologies. Whilst the phyletic position of Oesia is very uncertain, a place in the hemichordates may be worth exploring.
    Źródło:
    Acta Palaeontologica Polonica; 2009, 54, 1; 175-179
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Cambrian chaetognaths recognized in Burgess Shale fossils
    Autorzy:
    Szaniawski, H
    Powiązania:
    https://bibliotekanauki.pl/articles/20273.pdf
    Data publikacji:
    2005
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    Oesia disjuncta
    fossil
    Burgess Shale
    paleobiology
    protoconodont
    Canada
    Cambrian
    Chaetognatha
    chaetognath
    Opis:
    Oesia disjuncta, one of the species of the soft−bodied fauna collected and described by Walcott (1911) from the Middle Cambrian Phyllopod Bed (Burgess Shale, British Columbia, Canada) is recognized as a chaetognath. For anatomical comparisons many specimens of Recent chaetognaths were specially compressed and dried to obtain forms similar to the fossils preserved in shales. The most characteristic features shared by the fossil and Recent specimens include: strongly elongated, transversely striated and very flexible body, large size, and characteristically diversified shape of head, pronounced intestine and horizontally oriented caudal fin. Possible traces of other chaetognath structures—grasping apparatus, lateral fins, seminal vesicles, ventral ganglion, ovaries and anus—are also present but preserved in one specimen only. Among extant genera, those showing the closest similarity to Oesia Walcott, 1911 are the hyperbenthic Archeterokrohnia Casanova, 1986¹, and Heterokrohnia Ritter−Záhony, 1911, which are considered by some authors as evolutionarily most primitive.
    Źródło:
    Acta Palaeontologica Polonica; 2005, 50, 1
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    New evidence for the protoconodont origin of chaetognaths
    Autorzy:
    Szaniawski, H
    Powiązania:
    https://bibliotekanauki.pl/articles/20936.pdf
    Data publikacji:
    2002
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    phylogenesis
    paleobiology
    fossil
    Conodonta
    marine animal
    protoconodont
    Metazoan
    Cambrian
    chaetognath
    Chaetognatha
    body fossil
    Opis:
    An earlier hypothesis concerning the origin of chaetognaths from protoconodonts found additional support in new discoveries and in recent structural, chemical and molecular investigations. The new findings show that the head armature of protoconodonts was composed not only of grasping spines but also of much smaller spicules corresponding in size and shape to the chaetognath teeth. Grasping spines of protoconodonts were originally built mainly of an organic substance. Their original composition was changed by secondary phosphatisation. The thickest layer of the protoconodont spines was originally constructed of organic fibrils, similar to those in the corresponding layer of chaetognaths. Recent molecular investigations show that the chaetognath lineage separated in the early stage of metazoan radiation, which fits the presented hypothesis. Described are some previously unknown structural details of chaetognath grasping spines, including composition of the outer layer and the origin of their distinctive tips.
    Źródło:
    Acta Palaeontologica Polonica; 2002, 47, 3
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    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:
    Fossil chaetognaths from the Burgess Shale: A reply to Conway Morris [2009]
    Autorzy:
    Szaniawski, H
    Powiązania:
    https://bibliotekanauki.pl/articles/21244.pdf
    Data publikacji:
    2009
    Wydawca:
    Polska Akademia Nauk. Instytut Paleobiologii PAN
    Tematy:
    paleontology
    chaetognath
    fossil
    new genus
    new species
    Middle Cambrian
    Chaetognatha
    Oesia disjuncta
    polychaete annelid
    Cambrian
    Amiskwia sagittiformis
    Opis:
    Walcott (1911) erected the new genus and species Oesia disjuncta and assigned them to the polychaete annelids, based on a small collection of similar fossils from the famous Middle Cambrian Burgess Shale. In 2002 I suggested that the species is “possibly related to chaetognaths” (Szaniawski 2002: 405). Later, after obtaining new photos of the specimens and making comparative investigations with the extant chaetognaths, I was able to describe many significant similarities, and came to the conclusion that O. disjuncta indeed is an ancestral chaetognath (Szaniawski 2005). This interpretation already has been accepted in several publications (Vannier et al. 2005; Ball and Miller 2006; Hu et al. 2007. Giribet 2008). Ball and Miller (2006: 594) confirmed not only its “... remarkable resemblance to modern chaetognaths” but also correctness of recognition of all its organs. They even reproduced a part of my illustration showing them (Ball and Miller 2006: fig. 2). Vannier et al. (2006: 629) combined the problem with the open question of the systematic position of another Burgess Shale fossil Amiskwia sagittiformis Walcott, 1911, and expressed their reservation based on “...the lack of clear evidence of a grasping apparatus...”. Only Conway Morris (2009) firmly disagreed with this diagnosis and even devoted a special “discussion” article addressing the issue. However, that article contains several ambiguities and misunderstandings which need clarification.
    Źródło:
    Acta Palaeontologica Polonica; 2009, 54, 2; 361-364
    0567-7920
    Pojawia się w:
    Acta Palaeontologica Polonica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-5 z 5

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