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2 Acta Palaeontologica Polonica

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Large Onychites (Cephalopod Hooks) from the Upper Jurassic of the Boreal Realm

100%

Hammer O. , Hryniewicz K. , Hurum J. H. , Hoyberget M. , Knutsen E. M. , Nakrem H. A.

nr 4

We report on the discovery of large cephalopod arm hooks (mega−onychites) from the Kimmeridgian and Volgian of Spitsbergen (Agardhfjellet Formation). This includes a largely uncompressed hook in a seep carbonate, with preservation of surface sculpture. We suggest the use of logarithmic spirals as morphological descriptors for the outer part of cephalopod arm hooks, with implications for systematics and functional morphology. Comparison with Upper Jurassic material from Greenland, northern Norway and the North Sea demonstrates a remarkably consistent morphology, which we assign to the same form species, Onychites quenstedti. Considering the relatively small stratigraphic (Kimmeridgian–Volgian) and biogeographic (Boreal) range of this large form, it is likely that it represents a single biological species or genus.

A late Paleocene fauna from shallow-water chemosynthesis-based ecosystems, Spitsbergen, Svalbard

84%

Hryniewicz K. , Amano K. , Bitner M. A. , Hagstrom J. , Kiel S. , Klompmaker A. A. , Mors T. , Robins C. M. , Kaim A.

tom 64

nr 1

We present a systematic study of late Paleocene macrofauna from methane seep carbonates and associated driftwood in the shallow marine Basilika Formation, Spitsbergen, Svalbard. The fauna is composed of 22 taxa, comprising one brachiopod, 14 bivalves, three gastropods, three crustaceans, and one bony fish. The reported fish remains are among the first vertebrate body fossils from the Paleogene of Spitsbergen. One genus is new: the munidid decapod Valamunida Klompmaker and Robins gen. nov. Four new species are described: the terebratulide brachiopod Neoliothyrina nakremi Bitner sp. nov., the protobranch bivalve Yoldiella spitsbergensis Amano sp. nov., the xylophagain bivalve Xylophagella littlei Hryniewicz sp. nov., and the munidid decapod Valamunida haeggi Klompmaker and Robins gen. et sp. nov. New combinations are provided for the mytilid bivalve Inoperna plenicostata, the thyasirid bivalve Rhacothyas spitzbergensis, the ampullinid gastropod Globularia isfjordensis, and the munidid decapod Protomunida spitzbergica. Thirteen taxa are left in open nomenclature. The fauna contains a few last occurrences of Cretaceous survivors into the Paleocene, as well as first occurrences of Cenozoic taxa. It is composed of chemosymbiotic thyasirid bivalves and background species common in the northern Atlantic and Arctic during the Paleocene. Our results provide no evidence for a Paleocene origin of vesicomyid and bathymodiolin bivalves typical for Eocene and younger seep environments; instead, the Paleo cene seeps of the Basilika Formation are more similar to their Late Cretaceous equi valents rich in thyasirids.