A plesiosaur skeleton from the base of the Greenhorn Limestone (lower upper Cenomanian), western South Dakota, represents a new taxon tentatively referred to the Polycotylidae. The specimen possesses a number of features in common with the Polycotylidae, including an exceptionally elongate muzzle and mandibular symphysis, lack of a parietal foramen, homodont dentition, and faint striae only on the medial side of teeth. However, the palate and limb morphologies differ with respect to Polycotylidae as currently known. The pterygoids are united along their midline anterior to the parasphenoid, lacking an anterior interpterygoid vacuity. The preserved parasphenoid is relatively robust, possesses a strong ventral keel, and is sutured to the dorsal surface of the pterygoids. The paddles possess many plesiomorphic features, including only relatively minor posterodistal expansion of the propodials, epipodials that are longer than wide, a distinct antebrachial foramen, and relatively elongate phalanges. Derived features make it a plausible representative sister taxon to Polycotylidae, a prospect that is complemented by its stratigraphic position. This hypothesis is hampered by the palate morphology, which suggests a separate lineage of short-necked plesiosaurs far removed from genera classically assigned to Polycotylidae ( Dolichorhynchops , Polycotylus , Trinacromerum ). Nevertheless, the specimen represents the persistence of plesiomorphic limb traits and possession of a closed palate within an early polycotylid lineage until at least the early late Cenomanian in the Midcontinent of North America.

Abstract A partial exoccipital–opisthotic from the uppermost lower Campanian (Upper Cretaceous) of the Åsen locality, Kristianstad Basin, southernmost Sweden, is described and illustrated. The fossil represents the first braincase element of a plesiosaur found in Sweden. It includes the chamber for the ampulla and utriculus, openings for the caudal vertical and horizontal semicircular canals, and four foramina for cranial nerves. The incomplete braincase can be referred to an elasmosaurid plesiosaur, and closely resembles the exoccipital–opisthotic of Libonectes morgani and a referred specimen of Aristonectes parvidens . Although we discuss putative postcranial material of the elasmosaurid subfamily Aristonectinae in the uppermost lower Campanian of southernmost Sweden, the exoccipital–opisthotic from Åsen most likely belongs to a juvenile individual of a non-aristonectine elasmosaur.