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A rare coleoid mollusc from the Upper Jurassic of Central Russia

100%

Doguzhaeva L. A.

Acta Palaeontologica Polonica

2000

tom 45

nr 4

The shell of the coleoid cephalopod mollusc Kostromateuthis roemeri gen. et sp. n. from the lower Kimmeridgian of Central Russia consists of the slowly expanding orthoconic phragmocone and aragonitic sheath with a rugged surface, a weakly developed post-alveolar part and a long, strong, probably dorsal groove. The sheath lacks concentric structure common for belemnoid rostra. It is formed by spherulites consisting of the needle-like crystallites, and is characterized by strong porosity and high content of originally organic matter. Each spherulite has a porous central part, a solid periphery and an organic cover. Tubular structures with a wall formed by the needle-like crystallites are present in the sheath. For comparison the shell ultrastructure in Recent Spirula and Sepia, as well as in the Eocene Belemnosis were studied with SEM. Based on gross morphology and sheath ultrastructure K. roemeri is tentatively assigned to Spirulida and a monotypic family Kostromateuthidae nov. is erected for it. The Mesozoic evolution of spirulids is discussed.

Maastrichtian Ceratisepia and Mesozoic cuttlebone homeomorphs

70%

Hewitt R. A., Jagt J. W. M.

Acta Palaeontologica Polonica

1999

tom 44

nr 3

305-326

The phylogenetics of potential Mesozoic ancestors of cuttlefish of a restricted order Sepiida von Zittel, 1895 (superorder Decabrachia Boettger, 1952) is reviewed. Microstructural studies of Mesozoic homeomorphs of cuttlebones (Pearceiteuthis gen. n., Loligosepia, Trachyteuthis, Actinosepia) are consistent with their assignement to the superorder Octobrachia Fioroni, 1981. The discovery of an embryonic Ceratisepia shell in the upper Maastrichtian of the Netherlands, indicates that true Sepiida did have a pre-Cenozoic origin. Cretaceous decabrachs of the order Spirulida Stolley, 1919 do not show evidence of the dorso-anterior shell growth vectors seen in Cenozoic spirulids, sepiids and octobrachs. Separate origins of the Sepiida and Spirulida within Cretaceous diplobelinid belemnites is still the most attractive hypothesis. Ceratisepia vanknippenbergi sp. n. from the upper Maastrichtian of the Netherlands and Pearceiteuthis buyi gen. et sp. n. from the Callovian of England are described.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Doguzhaeva L. A.

1 Hewitt R. A.

1 Jagt J. W. M.

1 2000

1 1999

Wyniki wyszukiwania

A rare coleoid mollusc from the Upper Jurassic of Central Russia

Maastrichtian Ceratisepia and Mesozoic cuttlebone homeomorphs