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Siphuncular structure in Ordovician endocerid cephalopods

100%

Mutvei H.

Acta Palaeontologica Polonica

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1997

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tom 42

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nr 3

375-390

Exceptionally well-preserved shells of the endocerids Dideroceras wahlenbergi (Foord, 1887), Anthoceras vaginatum (Schlotheim, 1820), and Suecoceras barrandei (Dewitz, 1880) from phosphatized Early and Middle Ordovician limestones of Northern Estonia were studied by means of SEM. The septal neck in these endocerids is composed of three, structurally different, aragonite layers: outer spherulitic-prismatic, nacreous, and inner prismatic. The connecting ring is a continuation of the spherulitic-prismatic layer of the septal neck. Its inner surface was probably covered by a thin glycoprotein (conchiolin) sheet. Structural differentiations in the spherulitic-prismatic layer of the connecting ring, such as a layering and 'eyelet', reported by previous writers, were not observed. These differentiations probably result from diagenesis. The siphuncular structure in endocerids agrees in detail with that in Recent Spirula and Nautilus. The conical endosiphuncular deposits (endocones) of endocerids show extensive intraspecific variation. Morphological and structural differences in these deposits should therefore be used with caution in generic and specific diagnoses.

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Functional morphology and taphonomy of nautiloid beaks from the Middle Triassic of Southern Germany

88%

Klug C.

Acta Palaeontologica Polonica

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2001

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tom 46

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nr 1

New records of nautiloid beak elements conventionally classified as 'Rhyncholithes hirundo (Biguet, 1819)' and 'Conchorhynchus avirostris (von Schlotheim, 1820)' with carbonised (originally chitinous) three-dimensionally preserved appendages from the Upper Muschelkalk (Middle Triassic) of northern Württemberg (Southwest Germany) enable restoration of the complete beak of Germanonautilus. In three specimens, the lower mandible is embedded within the living chamber of Germanonautilus conchs, Beak elements of Germanonautilus differ from those of Recent Nautilus in the more elongate appendages of the fossil lower mandibles and the weaker sculpture on the originally chitinous parts. Furthermore, the dorsal sculpture of the fossil conchorhynchs consists of ridges rather than denticles and the ventral sculpture of the fossil rhyncholiths displays ridges in places where the Recent rhyncholiths have a smooth surface. Additionally, the fossil beak elements attained a larger size than their Recent counterparts, During transport of 'Rhyncholithes hirundo', the light chitinous parts served as a sail and the heavier conchorhynch anchored in the sediment causing alignment. In contrast to the irregularly embedded isolated rhyncholiths, the conchorhynchs usually settled with their ventral side up. From the study of 407 fossil nautiloid beak-elements, a significant variability of the hard parts is evident. Consequently, the assignment of specific morphologies to the species of Germanonautilus is impossible.

3

Zyjace skamienialosci

88%

Ryszkiewicz M.

Wiedza i Życie

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2003

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nr 11

58-60

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Wiedza i Życie

1 Klug C.

1 Mutvei H.

1 Ryszkiewicz M.

1 2003

1 2001

1 1997

Siphuncular structure in Ordovician endocerid cephalopods

Functional morphology and taphonomy of nautiloid beaks from the Middle Triassic of Southern Germany

Zyjace skamienialosci