Pachycostasaurus is approximately 3.1 meters long. Its rib cage and vertebrae exhibit thickened bone (Cruickshank et al. 1996) a condition termed pachyostosis. This heavy ossification is unusual in plesiosaurs (another exception may include Kronosaurus), although it is common in basal sauropterygians, especially pachypleurosaurs.
‘Occitanosaurus’ was described by Sciau et al. (1990) and Bardet et al. (1999). The genus name was erected for ‘Plesiosaurus’ tournemirensis by Bardet et al. (1999). The taxon was originally regarded as an early elasmosaurid but is now considered a member of the Microcleididae.
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.
M. victor was originally described and figured by Fraas (1910). Historically, M. victor has been regarded as a species of Rhomaleosaurus and is often associated in the literature under the defunct name ‘Thaumatosaurus’.
Macroplata has a unique character in its pectoral girdle: a distinct notch on the posterior border of the coracoid. The number of rib facets varies along the cervical vertebral column (27 in total) there is only one in the anterior vertebrae but two in the posterior ones.
Liopleurodon is a pliosaur that hardly needs introduction since appearing as the villain in the BBC’s ‘Walking with Dinosaurs’ TV series. This led to popular misconceptions about the size of Liopleurodon, which is known to have reached adult sizes in the region of seven metres long, nowhere near the gargantuan 25m estimate proposed by the series and later perpetuated elsewhere.
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.
Lower Cretaceous plesiosaurs are rare, so Leptocleidus is important because it fills a gap in the fossil record of plesiosaurians. Leptocleidus was once considered to be a late surviving member of the family Rhomaleosauridae but it has recently been reidentified as a close relative of polycotylids.
