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Wyszukujesz frazę "Clemens, W A" wg kryterium: Autor


Wyświetlanie 1-2 z 2
Tytuł:
Mammalian evolution during the Cretaceous-Tertiary transition; evidence for gradual, non-catastrophic patterns of biotic change
Autorzy:
Clemens, W.A.
Powiązania:
https://bibliotekanauki.pl/articles/23170.pdf
Data publikacji:
1983
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Opis:
Hypotheses invoking catastrophic causal factors for terminal Cretaceous extinctions call for, 1) instantaneous, global extinctions, 2) resulting from a single or dominant causal factor. Currently available methods of correlation are not precise enough to test the first element of these hypotheses. Patterns of mammalian extinction and survival in northeastern Montana, USA — as well as records of other organisms — argue against the second element. In Montana most of the lineages of marsupials were decimated. Extinction of multituberculates was not as severe, while only one lineage of eutherians appears to have become extinct. Groups that apparently immigrated into northeastern Montana just prior to the end of the Cretaceous had a greater probability of survival than the residents. The probability of extinction was independent of individual body size. Different patterns of mammalian extinction in different environments also appear to defy explanation in terms of one common, catastrophic causal factor.
Źródło:
Acta Palaeontologica Polonica; 1983, 28, 1-2
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
First record of a Jurassic mammal [?'Peramura'] from Ethiopia
Autorzy:
Clemens, W A
Goodwin, M.B.
Hutchison, J.H.
Schaff, C.R.
Wood, C.B.
Colbert, M.W.
Powiązania:
https://bibliotekanauki.pl/articles/21748.pdf
Data publikacji:
2007
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Ethiopia
tooth fragment
first record
mammal
Peramura
Mammalia
Jurassic
Mugher Mudstone
paleontology
Opis:
The first record of Mesozoic mammals in Ethiopia is a fragment of a lower mammalian molar discovered in residues left after acid dissociation of a small (ca. 4 kg) geological hand sample of a fine−grained bone bed in the lower part of the Mugher Mudstone exposed in the valley of the Jema River. This bone bed is part of a series of estuarine to fluvial deposits that are thought to be of Late Jurassic (Tithonian) age. The fragment preserves the trigonid of a molar; the distal part of its crown is missing. Morphological characters of the trigonid indicate the specimen (JEM−5/21) documents the presence of a mammal with a dentition at either a derived pretribosphenic or primitive tribosphenic grade of evolution. Absence of a well developed basal cingulid around the mesial end of the crown argues against phylogenetic relationships to the australosphenidans. Loss of the distal portion of the crown removed characters critical for determining its grade of evolution. The working hypothesis that JEM−5/21 represents a “peramuran” is advanced for testing. Hypotheses that it represents a mammal with a more derived grade of molar evolution or a previously unknown group of mammals cannot be excluded. JEM−5/21 establishes the presence of mammals in Ethiopia during the Late Jurassic, and its discovery identifies a fossil locality warranting thorough future exploration.
Źródło:
Acta Palaeontologica Polonica; 2007, 52, 3
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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