Fossils from Lyon Nunataks (74° 52′ S, 74° 02′ W) are described:Conodicoelitesspp.,Rotulariasp. indet., indet. pectinacean: cf.Entolium, andVariamussium lyonensissp. nov. Upper Jurassic (?Lower Kimmeridgian) age. TheConodicoelitesspp. have strong affinities with those of the New Zealand Lower Kimmeridgian. Ammonites, belemnites, andInoceramus, all with strong Indo-Pacific affinities, are present in the Kimmeridgian and Lower Tithonian of Central and South America, and the Lyon Nunataks fossils appear to be a southerly extension of this fauna. These fossil occurrences strongly suggest that a trans-Pacific migration route, probably skirting Antarctica, was available in Kimmeridgian and Lower Tithonian times. Faunal movements along this southern route are discussed in terms of: (1) Migration across existing oceans; (2) Migration between existing land masses, aided by connecting shelf areas; (3) Migration skirting formerly contiguous land masses. Continental drift is seen as a means of providing shallow-water migration routes between New Zealand, West Antarctica, and South America. Various continental reconstructions are considered, and one first published by King (1958) is preferred.