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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.
Acknowledgments
We extend our gratitude to the officers and crew of the NApOc Ary Rongel (Brazilian Navy) for their invaluable logistical support. Special thanks to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for funding (Grant No. 88887.596134/2020-00 for ROS). This work also received support from the National Council for Scientific and Technological Development (CNPq) and the Brazilian Antarctic Program (PROANTAR) under Project FLORANTAR (Grant No. 442765/2018-5 PROANTAR/CNPq). We are also grateful to the helpful comments and suggestions of Jack Cooper and the other two anonymous reviewers, as well as to the editors of Historical Biology, as they helped to substantially improve our manuscript. We acknowledge Gabriel Teófilo-Guedes for the interpretative life-reconstitution of the new shark species. Our appreciation goes to Dr. Rodrigo Lopes Ferreira and Pedro Henrique Mendes Carvalho from the Center for Studies on Subterranean Biology, Federal University of Lavras (Brazil), for providing access to and support for the use of a ZEISS Axio Stereomicroscope for imaging the specimen. We are grateful to Dr. Sergio Marenssi (Universidad de Buenos Aires and CONICET) and Dr. Manuel Jesús Montes Santiago (Instituto Geológico y Minero de España) for their valuable discussions concerning the limits of units 9-9g-10 of the López de Bertodano Formation. Special thanks to Ms. Luiza Carine Ferreira da Silva (UNISINOS) for providing clarifications on the local stratigraphic section. We also express our gratitude to the colleagues who shared the 57-day camping experience of the Brazilian Antarctic Program at Seymour (Marambio) Island (December 9, 2019, to February 2, 2020), especially climber and photographer Edson Vandeira for his field support, assistance in data collection, and providing the aerial image in Figure 2C. We also honor the enduring legacy and profound impact of the monumental, meticulous, and passionate work of Dr. Henri Cappetta. Passed away on January 6, 2024, Dr. Cappetta was a champion in the field of systematics and evolution of fossil elasmobranchs. His groundbreaking research not only expanded our understanding of ancient aquatic ecosystems but also served as a beacon of inspiration for countless researchers in the field.
Disclosure statement
No potential conflict of interest was reported by the authors.