Article: The skull of the Callovian plesiosaur Cryptoclidus eurymerus, and the sauropterygian cheek

Mechanical preparation of a relatively complete new skull specimen of Cryptodidus eurymerus has revealed the palate and cheek regions for the first time, permitting a more accurate reconstruction to be given. The wider phylogenetic implications of differing cheek and orbit configurations in sauropterygians are discussed and a cladogram given: the Cryptoclididae and the remaining plesiosauroids are sister groups; deep ventral cheek excavation arose through loss of the diapsid lower temporal arch and is a shared derived character of cryptoclidids, whereas an enlarged orbit and narrow vertical jugal bar are apomorphies. The palatal and mandibular structure of Cryptodidus is derived in comparison with pliosauroids: coronoids, prearticulars, suborbital fenestrae and the large pterygoid flange are all absent. These differences relate to feeding habit: Cryptodidus fed on small soft-bodied prey, and shows no adaptations for resisting torsional forces upon the jaws. Underwater olfaction similar to the pliosauroid system may have been present in Cryptodidus.