Mosasaurs from Antarctica have been recovered from the late Campanian and early and late Maastrichtian in James Ross, Vega and Seymour Islands within the James Ross basin. Tylosaurinae are represented by the late Campanian-early Maastrichtian remains of Taniwhasaurus antarcticus [Novas et al., 2002] and by late Maastrichtian Tylosaurinae indet.; Plioplatecarpinae by late Maastrichtian Plioplatecarpus sp.; and Mosasaurinae by late Maastrichtian “Liodon” sp., Mosasaurus sp. and Mosasaurinae indet. Materials from Cape Lamb, recently identified in the Museo de La Plata collection (Argentina), suggest that the stratigraphic range of Plioplatecarpus and “Liodon” within the James Ross basin extends back to the early Maastrichtian. At present, the holotype of T. antarcticus is the most complete specimen exhumed from Antarctica. In northern Patagonia, mosasaurs have been recovered from the late Maastrichtian of the Jagüel Formation, Neuquén basin. Patagonian mosasaurs are represented by Mosasaurus sp. aff. M. hoffmanni, Plioplatecarpus sp., Prognathodon sp., and Mosasaurinae indet. Presently, no Tylosaurinae have been found in Patagonia. Both in the James Ross and Neuquén basins, Mosasaurus sp. and Plioplatecarpus sp. occurred close to the K/Pg. boundary.