Additions to the diversity of elasmosaurid plesiosaurs from the Upper Cretaceous of Antarctica

• A probable new taxon of elasmosaurid plesiosaur from the upper Maastrichtian of Seymour Island.
• First evidence of a very-long necked elasmosaurid in the upper Campanian of James Ross Island.
• Oldest record of an aristonectine in the upper Campanian of James Ross Island.

Three specimens of elasmosaurid plesiosaurs (Sauropterygia, Plesiosauria) from Upper Cretaceous beds of Antarctica are described here. These include postcranial remains of a single adult individual recovered from late Maastrichtian beds of Marambio (= Seymour) Island, possessing a distinctive combination of features: cervical vertebrae having centra with a triangular outline in transverse section, a vertical groove on the rostral and caudal edge of the neural spines, and a deep articulation over the neural arch for the following postzygapophysis, while the scapula shows an unusually large and anteriorly recurved dorsal process. This combination of features is unknown in any adult, postcranial elasmosaurid genus recovered to date in the Upper Cretaceous of the Weddellian Biogeographic Province and could represent a new form. Additional specimens from James Ross Island comprise the first record of an Aristonectinae (Plesiosauria, Elasmosauridae) in late Campanian beds, being the oldest known record of this sub-family. Finally, a third specimen from the same age and locality reveals the presence of very-long necked elasmosaurids with affinities to typical representatives from the Upper Cretaceous of the Northern Hemisphere. These findings add to the known diversity of Upper Cretaceous elasmosaurids in high latitudes of the Southern Hemisphere.

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