A new species of cow shark (Hexanchiformes: Hexanchidae) from the Late Cretaceous of Seymour Island, Antarctica

Abstract

ABSTRACT A new Xampylodon species is described based on a distinguished fossil tooth from Antarctica. The specimen comes from the uppermost level of the informal unit 9 of the Late Cretaceous (Maastrichtian) López de Bertodano Formation, 9 metres below the Cretaceous/Palaeogene boundary in Seymour Island, Antarctic Peninsula. Hexanchid sharks are relatively rare in this unit, being represented by only two species: Notidanodon pectinatus and Xampylodon dentatus. The new taxon exhibits a combination of dental features traditionally known in both Xampylodon and Notidanodon (e.g. teeth flattened labio-lingually and bearing well-developed mesial cusplets, followed by a large acrocone), but the presence of a deep root and a distally bent crown indicates a closer similarity with the former. As X. brotzeni and X. loozi, but unlike X. dentatus, the new taxon bears more than five mesial cusplets. Uniquely derived characters include the presence of a pronounced gap between mesial cusplet one and two and a pattern of non-continuous serial enlargement of the mesial cusplets. Incorporating this discovery into the spectrum of Antarctic shark diversity suggests a richness in the southern polar region at the end of the Mesozoic era that surpasses the already considerable previous assessments of diversity.