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1 Acta Geologica Polonica

1 2010

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Late Cretaceous nautilid beaks from near-shore/shallow water deposits of the Bohemian Cretaceous Basin (Czech Republic)

Kostak M., Vodrazka R., Frank J., Mazuch M., Marek J.

Acta Geologica Polonica

2010

Vol. 60, no. 3

417-428

More than 30 isolated nautilid jaws have been discovered in washed samples of late Cretaceous (turonian) nearshore/shallow water deposits located in the southern part of the Bohemian Cretaceous Basin (BCB). upper and lower jaws discovered in genetically-similar early turonian deposits are described in detail herein. the nautilid jaw apparatuses comprise rhyncholites (upper jaws) assigned to Nautilorhynchus simplex (Fritsch), and conchorhynchs (lower jaws) assigned to Conchorhynchus cretaceus Fritsch. some rhyncholites show signs of abrasion and corrosion, and may also form a substrate for sessile organisms. in one specimen, signs of acid digestion in the stomach of a predator were recognized. N. simplex is synonymized with "Rhyncholithus" bohemicus (till), "R". curvatus. (till), "R" rectus (till) and "R". curtus (till). the significant morphological variability observed in N. simplex is supported by biometric data. although the jaws were not found associated with body chambers, it is inferred from the extremely low nautilid biodiversity across the Cenomanian/turonian boundary interval in the BCB, and from the range and relative abundance of the only early turonian nautilid taxon present, that the jaws are probably referable to the genus Eutrephoceras hyatt and specifically to the common and long-ranging species E. sublaevigatum (d'Orbigny).