Clidastes propython: A small mosasaur from the Upper Smoky Hill Chalk Copyright © 2001-2008 by Mike Everhart Created  01/14/01- Updated 01/07/2008

Clidastes mosasaurs were the smallest in size of the three major groups of mosasaurs found in the Western Interior Sea during the deposition of the Smoky Hill Chalk and are among the most primitive of the known mosasaurs.  Maximum length was about 4 meters in the chalk and slightly larger in the Pierre Shale.  Clidastes was much more common along the Gulf Coast than in the Western Interior Sea.

Clidastes liodontus is found in the lower section of the chalk (late Coniacian) and may actually be one of the first mosasaurs to enter the seaway (see Martin and Stewart, 1977) during the Turonian.  Clidastes propython, however, arrived much later and is only found in the upper sections of the chalk.  According to Williston and others, it may have preferred to live much closer to shore and thus would not be well represented in the mid-ocean area where the chalk was deposited. 

This specimen was collected from Logan County in the Zone of Hesperornis (Stewart, 1990), in the vicinity of Hattin's (1982) Marker Unit 22 (early Campanian). It consists of most of the skull and about 25 vertebrae. Some of the specimen had eroded out before being discovered and was weathered into many fragments.  Other parts were recovered in situ.  The specimen is currently in a private collection.

The skull of Clidastes propython adapted from Williston (1898).

	The right and left dentarys of Clidastes propython.
	A medial view of the right and left dentarys.
	Looking down at the row of teeth in the left dentary. Clidastes has 18 teeth in each dentary.
	Anterior end of the left dentary.
	Another view of the left dentary.
	A view of the left lower jaw.
	A detail of two teeth in the left dentary.  Clidastes teeth are bicarnate, laterally compressed and are covered with a smooth enamel (Russell, 1967).

Five views of the quadrates of Clidastes propython. (left to right) 1). Anterior aspects of the left and right quadrates. 2) Posterior view of the left and right quadrates. 3)  A posterior view of the left quadrate laying against the right quadrate. 4) A posterior view of the right quadrate showing the stapedial pit. 5) A ventral view of the right quadrate showing the surface of the condyle that articulates with the lower jaw.

	A dorsal view of the frontal and parietal of  Clidastes propython. The parietal foramen is damaged in this specimen.
	A ventral view of the frontal and parietal of Clidastes propython
	A dorsal view of the frontal and post-orbital frontal.
	A dorsal view of the juncture of the premaxilla with the right and left maxillaries
	A ventral view of the premaxilla.
	A view of the suture between the right maxilla and the premaxilla

	A ventral view of the premaxilla and both maxillae of this specimen.  The wood frame was added to stabilize the anterior portion of the skull (muzzle) for display. Clidastes propython has 16 teeth on each maxilla, plus two on each side of the premaxilla.
	A posterior-ventral view of the basioccipital and occipital condyle.
	A left lateral view of the braincase and the paroccipital processes of the opisthotics.
	A ventral view of the braincase, including the basioccipital.
	A ventral view of the left pterygoid.  There are 11 broken teeth or alveoli for teeth on this fragment.
	The articulated cervical vertebrae of this specimen.   The axis is at the left of the series and includes the axis intracentrum.  In mosasaurs, the first two cervical vertebrae (atlas-axis) are actually made up of several smaller bones; the paired atlas neural arches, the atlas intracentrum, the atlas centrum, the axis and the axis intracentrum.

The type specimen of Clidastes propython was described by E. D. Cope in 1869 from a specimen found in Alabama.  The specimen is curated in the Academy of Natural Sciences in Philadelphia. These pictures were shot during my visit in November of 2002.

	A dorsal view of the skull of the type specimen of Clidastes propython Cope 1869 from Alabama. (ANSP 10193: Academy of Natural Sciences of Philadelphia, Philadelphia, PA.)
	A close-up dorsal view of the frontal and parietal of Clidastes propython Cope
	Ventral and dorsal views of the premaxilla and maxillas of Clidastes propython Cope.
	Four views of the right quadrate of Clidastes propython Cope.
	Front limb bones of Clidastes propython Cope.

Additional reading about Clidastes:

Bell, G. L. Jr., 1997. A phylogenetic revision of North American and Adriatic Mosasauroidea. pp. 293-332 In Callaway J. M. and E. L Nicholls, (eds.), Ancient Marine Reptiles, Academic Press.

Cope, E. D., 1869. [Remarks on fossil reptiles, Clidastes propython, Polycotylus latipinnis, Ornithotarsus immanis.]. Proc. Amer. Philos. Soc. xi p. 117.

Everhart, M. J., P. A. Everhart and J. Bourdon, 1997 Earliest documented occurrence of the mosasaur, Clidastes liodontus, in the Smoky Hill Chalk (upper Cretaceous) of western Kansas. Kansas Acad. Sci. Trans. 16(Abstracts):14.

Everhart, M. J., 2001. Revisions to the Biostratigraphy of the Mosasauridae (Squamata) in the Smoky Hill Chalk Member of the Niobrara Chalk (Late Cretaceous) of Kansas. Kansas Acad. Sci. Trans 104(1-2):56-75.

Hattin, D. E., 1982. Stratigraphy and depositional environment of the Smoky Hill Chalk Member, Niobrara Chalk (Upper Cretaceous) of the type area, western Kansas. Kansas Geological Survey Bulletin 225, 108 pp.

Kiernan, C. R., 1992. Clidastes Cope, 1868 (Reptilia, Sauria): Proposed designation of Clidastes propython Cope, 1869 as the type species. Bull. Zool. Nomencl. 49 p. 137-139.

Martin, L. D. and J. D. Stewart, 1977.The oldest (Turonian) mosasaurs from Kansas, Jour. Paleon., 51(5):973-975.

Russell, D. A., 1967. Systematics and morphology of American mosasaurs. Peabody Museum of Natural History, Yale University, Bulletin 23.

Williston, S. W., 1893. Mosasaurs, Part II: Restoration of Clidastes, Kans. Univ. Quart., 2(2):83-84, 1 plate.

Williston, S. W., 1898. Mosasaurs. The University Geological Survey of Kansas, Volume IV, Paleontology, Part V, pp. 81-347.

Wright, K. R., 1987. The mosasaur Clidastes: new specimens and new problems. Jour. Alabama Acad. Sci. 58(3):99. (Abs.)

Wright, K. R., 1988. The first record of Clidastes liodontus (Squamata, Mosasauridae) from the eastern United States, Jour. Vert. Paleon., 8(3):343-345.