Isotopic analysis on teeth specimens has suggested that this genus and Platecarpus may have entered freshwater occasionally, just like modern sea snakes.

[4] The generic name refers to how the vertebral processes allow the proximal heads of the vertebrae to interlock for stability and strength during swimming.

Even though the vertebrae lock together, the living animal would have still had a range of motion in the horizontal plane that is sufficient to allow for the high quality of swimming in shallow waters.

It possessed a delicate and slim form with an expansion of the neural spines and chevrons near the tip of the tail and this enabled it to chase down the fastest of prey.

Prefrontal forms small portion of posterolateral border of external nares, broad triangular ala projects laterally from supraorbital wing.

edge of surangular very thin Iamina of bone rising anteriorly to position high on posterior surface of coronoid.

Russell noted that his diagnosis was exclusively based on C. propython and C. liodontus and might not necessarily apply to C. sternbergii (later referred to its own genus, Eonatator) or C.

[6] Mosasaur teeth are of rather uniform morphology (with a few exceptions, such as in Globidens) with a pointed and curved tooth crown that sits on a pedicel composed of bone.

[7] Mosasaurs, including Clidastes, and snakes both share the traits of thecodont tooth implantation, and a recumbent position of replacement teeth.

[12] However, Lively (2019) questioned the referral of these remains to Clidastes due to their fragmentary nature and lack of apomorphies placing them in the genus to the exclusion of other mosasaurs.

The remains unearthed were that of a juvenile but are one of the best preserved and most complete mosasaurs collected from the state and is regarded as the generic holotype of Clidastes.

Due to good preservation of the caudals, Sternberg noted that the chevrons along the vertebrae were ankylosed to the center, which is not observed in other mosasaurs.

This synapamorphy was believed to aid in fitting the proximal heads snugly into the basins that hew out from the vertebrae almost locking them in place.

The dental and vertebral morphology of Clidastes is closer to that of Mosasaurus than to any other mosasaur, firmly placing it within the subfamily Mosasaurinae.

[14][15] There is also an undescribed form from the Mooreville Chalk Formation of Alabama that likely represents a new taxon on its own, informally dubbed "Clidastes moorevillensis", which can be distinguished from both C. propython and C. liodontus based on its dental characteristics.

[9] Clidastes liodontus was described from the late Coniacian to early Campanian Smoky Hill Chalk Member of the Niobrara Formation in Kansas.

[2] The type specimen of C. liodontus, consisting of maxillae, a premaxilla and dentaries from the Niobrara Formation of Kansas, was housed at the Bayerische Staatssammlung für Paläontologie and may have been destroyed in the Second World War.

[6] Russell (1967)[6] diagnosed the species in general as follows: "Premaxilla V-shaped in horizontal cross-section, small rostrum present anterior to premaxillary teeth.

Among these former species now seen as synonyms of C. propython are C. "cineriarum", C. "dispar", C. "velox", C. "wymani", C. "pumilus", C. "tortor", C. "vymanii, C. "stenops", C. "rex", C. "medius" and C. "westi".

The type specimen consists of a single vertebra from the anterior thoracic region, YPM 1601, collected in a marl pit near Swedesboro, New Jersey.

C. iguanavus can be differentiated in its central articulations, which are kidney-shaped in outline, with a stronger emargination dorsally for the spinal cord, and in the relatively stout proportions of the centrum.