Cryptoclidus

Cryptoclidus, often wrongly spelled ‘Cryptocleidus’ after Andrews (1909), is a moderately sized plesiosaur with adults about four metres long (Brown 1981). It is known from a large number of individual specimens from the Oxford Clay Formation. Fossils of Cryptoclidus are relatively common, and provide a complete ontogenetic sequence from very young to old adult individuals. This makes Cryptoclidus one of the most studied and best understood of all plesiosaurs.

The name Cryptoclidus was first introduced by Seeley (1892) as a “sub-genus of Muraenosaurus“. Seeley (1892) did not provide an explicit etymology for the name, but it comes from the Ancient Greek words κρυπτός (kryptos), meaning ‘hidden’, and κλεῖδες (kleîdes), meaning ‘clavicles’, because in ventral view much of each clavicle is overlapped and ‘hidden’ by the scapula.

Full mounted skeletons of Cryptoclidus can be seen in several major museums including the Musee Palaeontologique, Paris; the Natural History Museum, London; the Hunterian Museum, Glasgow; and the American Museum of Natural History, New York.

The genus has diagnostic teeth with reduced ornamentation. Each premaxilla contains six teeth, each maxilla 21 teeth, and each dentary 24-26 teeth. Cryptoclidus lacks suborbital fenestrae on its palate and has a large anterior interpterygoid vacuity. A small foramen is located along the postorbital-squamosal junction in C. eurymerus (Brown 1981).

Cryptoclidus used its numerous, tightly packed, small, sharp teeth, to catch squid and fish, or perhaps to sift silty sediments for benthic animals such as crustaceans.

C. richardsoni differs from C. eurymerus only in the form of its humerus, which is more expanded distally (Brown 1981). The genus and species ‘Apractocleidus teretipes‘ was introduced by Smellie (1916) for a specimen now regarded as an old-adult of Cryptoclidus (Brown 1981).