Cryptoclidus

Cryptoclidus is a genus of plesiosaur reptile from the Middle Jurassic period of England, France, and Cuba.

Discovery
Cryptoclidus was a plesiosaur whose specimens include adult and juvenile skeletons, and remains which have been found in various degrees of preservation in England, Northern France, Russia, and South America. Its name, meaning "hidden clavicles", refer to its small, practically invisible clavicles buried in its front limb girdle.

The type species was initially described as Plesiosaurus eurymerus by Phillips (1871). The specific name "wide femur" refers to the forelimb, which was mistaken for a hindlimb at the time. Fossils of Cryptoclidus have been found in the Oxford Clay of Cambridgeshire, England. The dubious species Cryptoclidus beaugrandi is known from Kimmeridgian-age deposits in Boulogne-sur-Mer, France. Cryptoclidus vignalensis, which is now considered undiagnostic, hails from the Jagua Formation of western Cuba.

In 2016, there was a report about a fragmentary Cryptoclidus postcranial skeleton from the Callovian deposits of Nikitino village in Spassky District, Ryazan Oblast, Russia, but later Zverkov et al. defined it as an intedermitate cryptoclidid.

Description
Cryptoclidus was a medium-sized plesiosaur, with the largest individuals measuring up to 4 m long and weighing about 737 - 756 kg. The fragile build of the head and teeth preclude any grappling with prey, and suggest a diet of small, soft-bodied animals such as squid and shoaling fish. Cryptoclidus may have used its long, intermeshing teeth to strain small prey from the water, or perhaps sift through sediment for buried animals.

The size and shape of the nares and nasal openings have led Brown and Cruickshank (1994) to argue that they were used to sample seawater for smells and chemical traces.

Classification
The cladogram below follows the topology from Benson et al. (2012) analysis.