Abstract The fossil record of terrestrial vertebrates from the Late Cretaceous of Antarctica is currently composed of non-avian and avian dinosaurs from the marine sediments of the James Ross Basin, Antarctic Peninsula (West Antarctica). Although two dinosaurian formational assemblages (Late Campanian/Early Maastrichtian and Late Maastrichtian) are known, the record is still scattered, and evolutionary scenarios are tentative. Ten non-avian dinosaurs have been reported from Coniacian to Maastrichtian deposits, along with possible sauropod footprints of Early Maastrichtian age from Snow Hill Island. Five avian dinosaurs have been recorded or described exclusively from the Maastrichtian. The presence of an advanced titanosaur with characteristic procoelous mid-caudal vertebrae in Snow Hill Island Formation at Santa Marta Cove implies that the group achieved a global distribution by the Late Campanian. The Late Campanian/Early Maastrichtian non-avian dinosaur (ankylosaurs, ornithopods and dromaeosaurid theropods) clades probably attained a near-cosmopolitan distribution before the Late Cretaceous, and some aspects of this hallmark ‘Gondwanan’ fauna may therefore reflect climate-driven provinciality, not vicariant evolution driven by continental fragmentation. Antarctic Late Cretaceous avian dinosaurs are rare. They are restricted to the Maastrichtian and consist of a cariamid?, gaviids, a charadriiform and the basal Anseriformes Vegavis , and provide the first strong evidence for a basal radiation of birds known to exist in the Cretaceous.

Abstract A diverse marine assemblage of vertebrate fossils has been collected in recent years under the auspices of the British Antarctic Survey from Seymour, James Ross and Vega islands east of the Antarctic Peninsula. The specimens were derived from the Late Campanian Santa Marta Formation, Early Maastrichtian Snow Hill Island Formation and the Early–Late Maastrichtian López de Bertodano Formation. Sharks, teleosts, plesiosaurs and mosasaurs are represented, but birds and sea turtles are absent from the BAS collections; neornithine birds have been previously reported from the Late Cretaceous deposits of Antarctica. Shark teeth are relatively abundant, but teleosts are seemingly under-represented. Plesiosaurs (Elasmosauridae) are more abundant and complete than mosasaurs, and juveniles of both marine reptile groups are relatively common. The marine lizards, mosasaurs, are taxonomically diverse as elsewhere in the world, but with relatively few individuals compared to the plesiosaurs, which are taxonomically limited. A converse relationship normally occurs at other lower latitude Late Cretaceous localities. Some of these abundances and appearances may be due to collection bias, particularly due to difficult collecting conditions and weathering, but certain distributions may be the result of high latitudes.

Elasmosaurid plesiosaur remains containing gastroliths have been recently recovered from the Late Cretaceous Cape Lamb Member of the Snow Hill Island Formation, Antarctic Peninsula, as well as from the Sharon Springs Formation of the Pierre Shale Group, South Dakota. The significance of the Antarctic specimens lies in the large number and relatively small size of the stones, whereas those from South Dakota and elsewhere have larger stones but relatively small numbers. All specimens compared are of relatively large elasmosaurids, and rib diameters indicate similar overall size. One testable hypothesis was whether or not the weight of the gastroliths might be similar among similarly sized individuals. However, comparisons between the gastroliths recovered from an Antarctic specimen and those recovered from the Pierre Shale show great differences in both the size and number of gastroliths. The total mass of the stones collected in the specimen from Antarctica was 3.0 kg, whereas those recovered from the South Dakota specimens totaled 2.2 kg and 8.3 kg, respectively. Perhaps not all stones originally within each plesiosaur were found, but efforts were designed to recover every stone. The number of stones recovered from the Antarctic plesiosaur was exceptionally large (2626) and appears to represent the most gastroliths recovered from a single plesiosaur. Those recovered from South Dakota elasmosaurids totaled only 124 and 253, respectively. Therefore, neither weight nor number of stones corresponds among these large individuals, perhaps mirroring the temporal or behavioral differences. Lack of correspondence among individuals furthers questions concerning the utilization of gastroliths for neutral buoyancy, ballast, or as an aid in digestion. Many parameters remain unexplored, and questions arise not only as to the utilization of the gastroliths but also as to whether physiology of the Antarctic plesiosaurs differs from those at lower latitudes.