Polycotylus
Polycotylus latipinnis was the first short-necked plesiosaur to be recognised in North America (Carpenter 1996), and the first polycotylid to be described and named (Cope 1869). It was established in the same volume that coined the name Elasmosaurus and contained the infamous ‘head on the wrong end’ reconstruction (Cope 1869). However, despite their equally long history, Polycotylus never achieved the...
Nakonanectes
Nakonanectes is a small elasmosaurid plesiosaur from the Bearpaw Shale of Montana, USA. It is known from a single moderately complete specimen including a particularly fine skull. It has a relatively short neck for an elasmosaur consisting of ‘only’ 39-42 neck vertebrae. However, 16–19 of the neck vertebrae were lost in a “heavy spring runoff that occurred between the time...
Styxosaurus
The holotype specimen (KUVP 1301) of Styxosaurus is an articulated skull and anterior portion of the neck. It was found in the Niobrara Chalk near Hell Creek, Logan County, Western Kansas in 1890. It was described later that year as a new species Cimoliosaurus snowii by Williston (1890a) (and in more detail soon after by Williston 1890b), who subsequently...
Ogmodirus
The type skeleton of ‘Ogmodirus’ was collected in 1909 by C. Boyce from the upper Greenhorn Limestone Formation (Lower Turonian, Upper Cretaceous) of Cloud County (near Aurora), Kansas (Storrs 1999, Schumacher and Everhart 2005). The specimen, KUVP 441, is a partial skeleton consisting of partial vertebral column (51 cervical vertebrae, 18 caudal vertebrae), limb, and girdle elements. Originally named...
Thalassomedon
The holotype of Thalassomedon was discovered by R. L. Landberg in 1939 in Baca County, Colorado. Thalassomedon has a short and deep atlas-axis and 62 cervical vertebrae, and there is no pectoral or pelvic bar in the adult condition (Carpenter 1999). The species name haningtoni is sometimes wrongly spelled ‘hanningtoni’ (as in Carpenter 1999) or ‘haringtoni’ (as in the AMNH...
Morturneria
The taxon was originally named ‘Turneria seymourensis‘ by Chatterjee and Small (1989) but this genus was preoccupied and so Chatterjee and Creisler (1994) later revised the name to Morturneria seymourensis. The holotype specimen is TTU P 9219, an incomplete skull and mandible plus associated cervical vertebrae, from the Lopez de Bertodano Formation of Seymour Island, Antarctica. Morturneria was regarded by...
Libonectes
Libonectes was erected for ‘Elasmosaurus morgani’. The pectoral girdle and a forelimb of the holotype are figured (most recently by Welles 1962, fig. 12) but now lost (Carpenter 1999). Libonectes morgani (Welles 1949) is the type and only species. Type material of L. morgani (SMUSMP 69120) consists of a skull, cervical vertebrae and gastralia, from the Britton Formation, Eagle...
Kaiwhekea
Kaiwhekea, also known as the ‘Shag Point Plesiosaur’, was classified as a cryptoclidid by Cruickshank and Fordyce (2002). More recent classifications regard it as an aristonectid. It has an unusually large number of small needle-like teeth and a shortened snout, much like the closely related Aristonectes. Kaiwhekea katiki is the type and only species. Reconstruction of the skull of Kaiwhekea...
Hydrotherosaurus
Hydrotherosaurus is a long-necked elasmosaurid from California, USA. It is represented by one of the most complete elasmosaurid skeletons ever discovered, so Hydrotherosaurus is one of the best known members of this family. The almost complete type skeleton of Hydrotherosaurus was discovered in the Panoche Hills by Mr. Frank C. Paiva in 1937, and was excavated by the University of...