Belying previous interpretations on its rarity in southern latitudes, Gaudryceras de Grossouvre is well represented in the Santonian—Campanian of Antarctica. The study of more than 300 specimens from the Santa Marta, Rabot and Snow Hill Island Formations designates five species that characterize four successive stratigraphic intervals: 1) Gaudryceras cf. G. strictum, Santonian, Alpha Member, lower part of the Santa Marta Formation; 2) Gaudryceras santamartense sp. nov., Santonian—early Campanian, Alpha Member, lower mid part of the Santa Marta Formation; 3) Gaudryceras brandyense sp. nov., late early Campanian—?basal mid Campanian, Beta Member, upper part of the Santa Marta Formation; and 4) Gaudryceras cf. G. mite and Gaudryceras rabotense sp. nov., mid Campanian—late Campanian, upper middle part of the Rabot Formation and lower part of the Hamilton Point Member of the Snow Hill Island Formation. There are two differently ornamented neanoconchs characterized by exhibiting dense or sparse strong flares, which are features of taxonomic importance at the specific level. In Antarctica, Gaudryceras is well represented from the Santonian to the mid Campanian, rare in the late Campanian and not known in the Maastrichtian. Such facts strongly contrast with data recorded outside Antarctica, particularly in the North Pacific, where Gaudryceras is well represented up to the late Maastrichtian. A striking biogeographical contrast is apparent for the Antarctic gaudryceratids. That is, while the early Campanian Gaudryceras brandyense sp. nov. and the mid-late Campanian G. rabotense sp. nov. are apparently restricted to Antarctica, the Santonian—early Campanian Antarctic species are very similar or co-specific to widely distributed forms.
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