Cryptoclidus, often wrongly spelled ‘Cryptocleidus’ after Andrews (1909), is a moderately sized plesiosaur up to 3 metres long. 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.
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. 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.
Cryptoclidus used its numerous 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. The genus and species ‘Apractocleidus teretipes‘ was introduced by Smellie (1916) for a specimen now regarded as an old-adult specimen of Cryptoclidus.




















Cryptoclidus eurymerus
Species
C. eurymerus
Author
(Phillips, 1871)
Classification
Sauropterygia
Eosauropterygia
Eusauropterygia
Pistosauroidea
Pistosauria
Plesiosauria
Plesiosauroidea
Cryptoclididae
Cryptoclidus
Age
Callovian, Late Jurassic
Type location
Peterborough, England
Type specimen
NHMUK 22656, complete skeleton.
Referred material
To be compiled
Cryptoclidus richardsoni
Species
C. richardsoni
Author
Lydekker, 1889
Classification
Sauropterygia
Eosauropterygia
Eusauropterygia
Pistosauroidea
Pistosauria
Plesiosauria
Plesiosauroidea
Cryptoclididae
Cryptoclidus
Age
To compile
Type location
Dorset
Type specimen
To comile
Referred material
To compile