Jurassic and Early Cretaceous selachians - focus on southern Scandinavia

Detta är en avhandling från Department of Geology, Sölvegatan 13, SE-223 62 Lund

Sammanfattning: The Jurassic and Early Cretaceous selachian faunas of Scania (Skåne), southern Sweden and the island of Bornholm (Denmark) have been investigated. Three Early Jurassic shark tooth assemblages have been recorded and investigated, one from Hettangian strata and the other two from Pliensbachian sediments. The Hettangian assemblage originates from non-marine deposits in the southern part of Helsingborg. The fauna comprises four hybodont taxa and is the first non-marine Hettangian assemblage to be recorded from northwest Europe. The two Pliensbachian faunas are both of marine origin but their composition is very different. Sediments of the Hasle Formation on Bornholm have yielded a fauna comprising three neoselachians and three hybodonts, including the new species Lissodus hasleensis. The other Pliensbachian assemblage, extracted from sediments of the Rya Formation at Katslösa in Scania, includes a single hybodont, five synechodontiforms, an indeterminate hexanchiform and Agaleus dorsetensis. The last species forms the basis of the new monotypic family, the Agaleidae. The non-marine Early Cretaceous of southern Scandinavia have yielded selachian assemblages where hybodonts are the dominating group. In southern Sweden, an assemblage comprising three hybodont species and an indeterminate squatinid has been found in the Berriasian part of the Vitabäck Clays. Two other small selachian tooth assemblages have been discovered within sediments of the Nyker Group on Bornholm. The combined fauna includes three hybodont taxa, of which two Hybodus species appear to be previously undescribed. The Berriasian selachian fauna of the Purbeck sediments in southern England has been revised. The hybodont component of this assemblage comprises six species occurring within a single bed and constituting the most diverse Berriasian hybodont fauna encountered so far. Two species of rhinobatoid rays occur in the Corbula beds, a unit where the mollusc fauna indicates higher palaeosalinity. Two selachian species within the Purbeck are new, Lonchidion inflexum and Belemnobatis variabilis. The hybodont genus Lissodus is revised and found to include a number of separate lineages. The revised record of Lissodus includes twelve species and has a stratigraphic range from the Scythian (Early Triassic) to the Albian (Early Cretaceous). Lonchidion is considered valid and includes thirteen named species and several undescribed species, ranging from the Ladinian (Middle Triassic) to the Maastrichtian (Late Cretaceous). Two new genera, the monotypic Vectiselachos from the Barremian (Early Cretaceous) and Parvodus including three species ranging from the Bathonian (Middle Jurassic) to the Valanginian (Early Cretaceous), are described and include former Lissodus species.

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