A proximal fragment of a gill raker identified as belonging to a shark of the genus Cetorhinus was collected from middle Eocene deposits of the La Meseta Formation in the northern part of Seymour Island, Antarctica. This is the first record of a fossil basking shark from Antarctica and one of the earliest records of the genus. The minimum age of Cetorhinidae is middle Eocene. The only living species of the family Cetorhinidae is a very large plankton feeder, Cetorhinus maximus. Basking sharks are unknown in subantarctic or Antarctic waters but occur on both South American coasts today. The evolution of filter-feeding vertebrates is discussed.
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