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. Besides being different in size, the teeth of Campanian species of
Mosasaurus (namely
M. missouriensis and
M. conodon) differ from those of
Clidastes in having a large number of facets that are also more distinct than those in
Clidastes. The cervical vertebrae of
Clidastes are also different from those in
Mosasaurus by being more elongated. }} There is only one named species of
Clidastes that is valid,
C. propython.
Clidastes iguanavus Cope, 1868 was the original type species, but the ICZN was petitioned to make
C. propython the new type species by virtue of that species being based on diagnostic remains, which it did vis-à-vis Opinion 1750 (1993).
Invalid species 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.
Clidastes propython models at the
North American Museum of Ancient Life.
C. propython is the best studied species of the genus, and was for this reason chosen by the ICZN to replace
C. iguanavus as the type species.
C. propython is known from the
Campanian of the
United States (
Alabama,
Colorado,
Texas,
Kansas and
South Dakota) and of
Sweden. The earliest known occurrences of the species are middle
Santonian in age and from the
Niobrara Formation of Kansas, whilst the latest are Middle to Late
Campanian in age, coinciding with a poorly understood middle Campanian intercontinental mosasaur extinction event, which seems to have heavily affected genera such as
Clidastes.
Russell (1967) listed the following unambiguous character states for the species: "Premaxilla V-shaped in horizontal cross-section, small. rostrum present anterior to premaxillary teeth. Posteroventral portion of root of second premadlary tooth exposed on sutural surface with maxilla. Premaxillo-maxillary suture rises posteriorly in gentle curve to terminate at point above seventh maxillary tooth. Premaxillary suture of maxilla smoothly keeled and paraIIels longitudinal axis of maxilla. Sixteen-18 teeth in maxilla. Median dorsal surface of parietal moderately broad. Parietal foramen small, lies close to suture with frontal and opens ventrally into elliptical excavation in parietal, length of which exceeds that of dorsal opening by about five times. Anterior border of prootic forms shelf beneath prootic incisure, then descends abruptly to basisphenoid. Foramen for cranial nerve VII leaves brain cavity through medial wall of prootic. Infrastapedial process present on quadrate. Seventeen to eighteen teeth in dentary.". Russell (1967) also referred a large number of fragmentary species of
Clidastes to
C. propython on the basis of that those with good cranial material were morphologically indistinguishable from the type specimen of
C. propython. 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".
Clidastes iguanavus The
Campanian C. iguanavus is the original type species of
Clidastes and poorly known in comparison to
C. propython and
C. liodontus. The type specimen consists of a single vertebra from the anterior thoracic region, YPM 1601, collected in a marl pit near
Swedesboro,
New Jersey. The vertebra is similar to that of the other species in its general proportions and the strong zygosphene-zygantrum articulation.
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. == References ==