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Soft-tissue attachment structures and taphonomy of the Middle Triassic nautiloid Germanonautilus

100%

Klug C., Lehmkuhl A.

Acta Palaeontologica Polonica

2004

tom 49

nr 2

New examinations of numerous steinkerns of the Middle Triassic nautiloid Germanonautilusfrom southern Germany revealed new anatomic, ecologic, and taphonomic details, which are compared with Recent Nautilus. The attachment structures of the cephalic retractor muscle (large scar) and of the dorsal (black layer) and the posterior mantle (posterior narrow scar, anterior band scar of the mantle and septal myoadhesive bands), some with tracking bands (recording the anteriorward movement of the soft body during ontogeny), were seen in several specimens. The shape and proportions of these soft−tissue attachment structures resemble those of Recent Nautilus macromphalus and indicate a similar soft part anatomy. Based on their conch geometry, the mode of locomotion of Germanonautilus is reconstructed. Owing to the wide whorl cross section and the high whorl expansion rate, drag of the conchs was high, the aperture was oriented at an oblique angle which made Germanonautilus a rather slow horizontal swimmer. Because of their large sizes and widths, conchs of Germanonautilus were often deposited on their broad venters, forming elevated “benthic islands” (secondary hardgrounds). A broad range of animals (fish, decapods, ophiurans, crinoids, brachiopods, bryozoans, bivalves, Spirorbis, foraminiferans) lived in and on these comparatively large secondary hardgrounds.

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

88%

Klug C.

Acta Palaeontologica Polonica

2001

tom 46

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.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Klug C.

1 Lehmkuhl A.

1 2004

1 2001

Wyniki wyszukiwania

Soft-tissue attachment structures and taphonomy of the Middle Triassic nautiloid Germanonautilus

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