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Wyświetlanie 1-2 z 2
Tytuł:
Geology and taphonomy of the base of the Taquaral Member, Irati Formation (Permian, Paraná Basin), Brazil
Autorzy:
Chahud, A.
Petri, S.
Powiązania:
https://bibliotekanauki.pl/articles/138649.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
taphonomy
permian
actinopterygii
sarcopterygii
Chondrichthyes
tafonomia
perm
promieniopłetwe
mięśniopłetwe
ryby chrzęstnoszkieletowe
Opis:
The taphonomy of Early Permian vertebrates from a sandy facies at the base of the Taquaral Member, Irati Formation, was surveyed in order to acquire data for the interpretation of the sedimentary processes and paleoenvironment of deposition. Six outcrops from the Rio Claro municipality and surrounding areas, from the Brazilian State of São Paulo, were investigated. The vertebrate groups are Chondrichthyes (Xenacanthiformes, Ctenacanthiformes and Petalodontiformes), Osteichthyes (Actinopterygii and Sarcopterygii) and Tetrapodomorpha. They occur as loose teeth, scales, spines and bone remains. The sandy facies is characterized by fining upward deposition. The coarser sandstone immediately above the underlying Tatuí Formation is rich in Chondrichthyes. However, the fine sandstone above, immediately beneath the silty shale facies, is devoid of Chondrichthyes, though Osteichthyes scales, teeth and bones were present. The taphonomy is important for inferring sedimentary processes and then the paleoenvironments. The poor sorting of the sandstone and the presence of fossils that are mostly abraded or worn are indicative of a high energy environment. In contrast, the presence of fossils in a good state of preservation, some without abrasion and breakages are indicative of only limited transport. Differences of fossil spatial density, numbers of specimens and taxa may be explained by the dynamics of deposition, from details of the palaeoenvironment can be obtained.
Źródło:
Acta Geologica Polonica; 2015, 65, 3; 379-387
0001-5709
Pojawia się w:
Acta Geologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A microanatomical and histological study of the postcranial dermal skeleton in the Devonian sarcopterygian Eusthenopteron foordi
Autorzy:
Zylberberg, L
Meunier, F.J.
Laurin, M.
Powiązania:
https://bibliotekanauki.pl/articles/20289.pdf
Data publikacji:
2010
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
paleontology
microanatomical study
histology
postcranial dermal skeleton
Devonian
sarcopterygian
Eusthenopteron foordi
Sarcopterygii
Tetrapodomorpha
Tristichopteridae
Eusthenopteron
elasmoid scale
paleohistology
transmission electron microscopy
Late Devonian
Frasnian
fossil record
Opis:
The fin rays and two types of scales (enlarged and regular) of the Devonian sarcopterygian Eusthenopteron foordi are redescribed using light, scanning and transmission electron microscopy. The fin rays consist of lepidotrichia composed of ossified, jointed and branched segment pairs. The basal segments are cylindrical, but more distal elements are crescentic in section. The distribution of Sharpey’s fibres varies along the lepidotrichia. In the proximal segments, lateral bundles form a belt connecting adjacent hemisegments. In the distal segments, thin bundles are restricted to the area facing the fin surface. Both enlarged and regular scales have a similar spatial organisation. They are composed of a superficial highly mineralised layer covering a thick basal plate where the fibrils are distributed in superimposed strata forming a plywood−like structure. Nevertheless, the enlarged and regular scales differ in their shape, in the mineralised tissues of the superficial layer, and in the organisation of the plywood−like structure. The superficial layer of the enlarged scales is composed of parallel−fibered bone covering a deeper layer of woven−fibered bone. The basal plate is made of an orthogonal plywood−like structure. The thin, lamellar, imbricated regular scales display the characteristics of elasmoid scales. The mineralised tissue forming the superficial layer resembles that of extant teleost scales. In the basal plate, the twisted plywood−like structure is composed of closely packed fibrils that are preserved down to the ultrastructural level owing to the persistence of bridges connecting the fibrils. The enlarged and the regular scales of Eusthenopteron foordi do not present superficial odontodes, in contrast to ancestral thick rhomboid scales. The disappearance of enamel/enameloid and dentine may be related to the evolutionary trend towards a lightening of the dermal skeleton that would improve the swimming abilities of the animal. The characteristics of the dermal skeleton of Eusthenopteron foordi support the hypothesis that this process began early in osteichthyans.
Źródło:
Acta Palaeontologica Polonica; 2010, 55, 3; 459-470
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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