Acta Palaeontologica Polonica

Lower Turonian record of belemnite Praeactinocamax from NW Siberia and its palaeogeographic significance

Martin Košťák and Frank Wiese

Acta Palaeontologica Polonica 53 (4), 2008: 669-678 doi:

Specimens of the belemnitellid Praeactinocamax Naidin, 1964 are described from the Upper Cretaceous of NW Siberia
(Taimyr Region, Lower Agapa River, Russia). The rostra determined as Praeactinocamax aff. plenus consist of an
aragonitic anterior part and a calcitic posterior part with a sharp boundary in between. This boundary surface is referred to as the “alveolar fracture”, and it is a typical morphological feature of early belemnitellids and not a result of diagenetic processes. The occurrence of Praeactinocamax in Arctic areas shows a wider palaeobiogeographical distribution of the genus in the Late Cenomanian–Early Turonian interval than previously known. This finding suggests that migration of the late Cenomanian–early Turonian fauna occurred across Turgai channel. The geographic position of these new records may also explain the occurrence of Praeactinocamax in the Turonian of the US Western Interior Seaway, the origin of which has been hitherto unclear.

Key words: Belemnitellidae, Praeactinocamax, palaeobiogeography, Cenomanian, Turonian, Upper Cretaceous, Northern Siberia, Russia

Martin Košťák [], Ústav geologie a paleontologie, Přírodovědecká fakulta UK, Praha 2, Alberov 6, 12843, Czech Republic; Frank Wiese [] Fachrichtung Paläontologie, FU Berlin, Malteserstr. 74-100, D-12249 Berlin, Germany.

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