Pachycostasaurus Cruickshank et al. 1996
Etymology: Pachus = thick, costa = rib, sauros = lizard. Pachycostasaurus is approx. 3.1 meters long. The 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 the pachypleurosaurs. Pachycostasaurus probably used the extra ballast provided by its heavy bones to traverse the sea bed searching for prey or to hide in ambush. Pachycostasaurus is been classified as a pliosaurid and is notable for its its delicately constructed skull and relatively short mandibular symphysis.
P. dawni Cruickshank et al. 1996 (type species)
Type material: PETMG R338, an almost complete skeleton including most of the skull and some of the mandible, almost complete vertebral column and associated ribs, left pelvis, right ilium, both humeri, three phalanges from a hindlimb.
Age and Location
Middle Jurassic (Callovian). Peterborough Member, Oxford Clay Formation (Jason Subzone), the King's Dyke Clay Pit, Wittlesey, Cambridgeshire, England.