Ectenosaurus clidastoides FHSM VP-401 A unique Kansas mosasaur with preserved skin   Copyright ©2011 by Mike Everhart     Page created 11/14/2011- Last updated 11/21/2011

Ectenosaurus clidastoides is a relatively rare mosasaur, currently known only from the Smoky Hill Chalk of western Kansas, USA. The species was initially described as Platecarpus clidastoides by Merriam (1894) from a specimen collected by C.H. Sternberg or G. Bauer from Logan County, Kansas. The type specimen was in the Bayerische Staatssammlung fur Palaontologie, but the specimen was probably destroyed in World War II:

In 1953, George Sternberg discovered a much better specimen (GFS 109-53) about 9 miles north of WaKeeney, Kansas. The mosasaur was about 9 feet in length, mostly articulated, but had previously lost the rear limbs and tail to erosion. Sternberg initially identified it in his field notes as Clidastes velox. His notes on the specimen are shown below:

The mounted specimen was on exhibit in Sternberg Memorial Museum on the campus of Fort Hays State University from the mid-1950s to 1999 when the museum was closed in preparation to move to the current location. Currently the specimen is in storage. It was examined in 1963 by Dale Russell, then of the American Museum of Natural History, and determined to be Platecarpus clidastoides instead of Clidastes velox. In a letter from Dale Russell to Myrl Walker, he indicated that it represented the only specimen of a rare mosasaur species, and that he would rename it as Ectenosaurus clidastoides in a future publication. Russell published his Systematics and Morphology of American Mosasaurs in 1967, and Ectenosaurus clidastoides (new genus) is officially re-described and named on page 156. The front limb and the skull in dorsal view were included as Text-figs. 54 and 86. Aside from Russell's (1967) description, nothing else has been published on this specimen other than Bell 1997, and mentions by Everhart 2000, 2005. A second specimen (FHSM VP-13746) was reported by Everhart (2004) from shark scavenged remains discovered in Gove County. Everhart (2005, fig. 9.5) published photos of the skull. The preservation of scales associated with this specimen was mentioned in a Masters thesis by Schumacher (1993) and further discussed in an unpublished thesis by Valerio (2008). 

In George Sternberg's 1953 note on the FHSM VP-401 specimen, there is an interesting statement: "These small section[s] of chalk rock show the fine scale impressions from a Cretaceous mosasaur, specimen #7937.   Russell (1967, p. 70) also mentioned that the Fort Hays Ectenosaurus specimen had scales, as did a Tylosaurus specimen (KUVP 1075) reported by Snow (1878a, 1878b, 1879) and a Platecarpus (KUVP 1001) reported by Williston (1898a). Williston (1898b, p. 215, pl. 69-70)  also commented on Snow's discovery and republished photographs of the Tylosaurus scale impressions. 

All of these specimens were collected from the Smoky Hill Chalk.  Subsequently, Lindgren, et al. (2009) reported scale impressions from a specimen of Plotosaurus in California, and Lindgren, et al. (2010) described scale impressions preserved in association with a Platecarpus specimen (LACM 128319) from western Kansas. The LACM 128319 scale impressions were first reported by Geist et al. 2002. 

Also, in August-October, 1951, G.F. Sternberg collected a fairly complete, 20 foot long Tylosaurus specimen (GFS 1-51; FHSM VP-327), including a 35 inch skull, from a roadside exposure along Highway 24 west of Hill City (Graham County) that included scale impressions in the abdominal region. The specimen was subsequently sent to the Los Angeles County Museum in an exchange, and has not been relocated.  All that remains in the records are three color photographs, two of which show the collected specimen (vertebrae, ribs and scale impressions) and the other which shows the locality. Sternberg's field notes indicated that the scales were fragile and might not be able to be saved. 

The latest report on mosasaur integument comes back to the FHSM VP-401 specimen.  On November 16, 2011, we reported not only the scale impressions of Ectenosaurus clidastoides (FHSM VP-401), but the three-dimensional, layered structure of the skin:

The photographs below show various aspects of the FHSM VP-401 specimen not previously published.

	LEFT: The skull of the Ectenosaurus clidastoides (FHSM VP-401) specimen in right dorso-lateral view.  RIGHT: The skull of the Ectenosaurus clidastoides (FHSM VP-401) specimen in ventral view, including the left lower jaw in lateral view.
	LEFT: The frontal-parietal bones, including the parietal foramen, of the Ectenosaurus clidastoides (FHSM VP-401) skull in dorsal view.  RIGHT: The orbit of the right eye of the Ectenosaurus clidastoides (FHSM VP-401) skull in lateral view, including the postorbital frontal, frontal, prefrontal and jugal.
	LEFT: The paired pterygoid bones of the Ectenosaurus clidastoides (FHSM VP-401) skull, partially exposed under the left lower jaw. RIGHT: The posterior corner of the Ectenosaurus clidastoides (FHSM VP-401) skull in right lateral view, including the squamosal, postorbital frontal and posterior portion of the jugal.
	LEFT: Dorsal and ventral views of the Ectenosaurus clidastoides (FHSM VP-401) skull. See labeled drawing from Russell (1967) here. RIGHT: Lateral and medial views of the right quadrate of the Ectenosaurus clidastoides (FHSM VP-401) skull.
	LEFT: A detail view of several teeth on the right maxilla of the Ectenosaurus clidastoides (FHSM VP-401) skull. RIGHT: A detail medial view of a complete tooth in the right maxilla, showing bud teeth forming in the medial side of the maxilla. The teeth are described by Russell (1967, p. 156) as "bicarinate, vertically striated and medially recurved."
	LEFT: The post-cranial skeleton of FHSM VP-401. The rear limbs and tail were lost to erosion prior to discovery by G. F. Sternberg RIGHT: Preserved cartilage of the sternal ribs and sternum of FHSM VP-401.
	LEFT: The well preserved front limbs of the FHSM VP-401 specimen. The fifth digit is apparently greatly reduced in Ectenosaurus clidastoides. RIGHT: A close-up photo of the left front paddle of FHSM VP-401. See labeled drawing from Russell (1967) here.
	The following four close-up photos were taken in 2005 when I became interested in what I thought were "just skin impressions" (Everhart 2005).  LEFT: A series of scale impressions in the matrix from the FHSM VP-401 Ectenosaurus clidastoides specimen. A note included with the specimen said that the impressions were discovered in the neck region of the specimen (between the lower jaws and the front limbs). RIGHT: Two more small fragments of the matrix with scale impressions. The scales measure about 2.7 mm in length by 2 mm in width, and where preserved, they are about 0.1 mm thick.
	LEFT: Another fragment of the matrix with scale impressions. Initially I had reported (Everhart 2005) that the scale impressions did not show a central keel, but upon closer examination it became evident that they do have a keel similar to those found in Tylosaurus (KUVP 1075).  RIGHT: Another fragment of the matrix with scale impressions.  This piece, however, does show some of the three-dimensionality of the preserved skin layers, including some of the associated fibrous structures. After the 2nd Mosasaur Meeting in May, 2007, Johan Lindgren and I started talking about the skin preservation in the Ectenosaurus specimen. That conversation continued during a September 2010 meeting at the University of Kansas when we examined the KUVP 1001 Platecarpus specimen for skin impressions. In the meantime, Lindgren and others (2009, 2010) had published papers regarding the discovery of scales in Plotosaurus and Platecarpus.
	In 2010, Johan and I began to look more critically at the FHSM VP-401 matrix fragments. As might be expected, the more we looked, the more structure we found.  The following six photos, taken through a binocular microscope and using a single light source, are examples of preserved scales, scale impressions, and underlying integument preserved in the matrix surrounding the bones of FHSM VP-401.   LEFT: This fragment preserves what appears to be the underside of the scales. RIGHT: Another fragment showing the underside of a group of scales, but also demonstrating layers of structure in the preservation.
	LEFT: This piece shows what appears to be the mid-line between two groups of scales, trending from lower left to upper right. as well as layers of structures. RIGHT: Another fragment showing the underside of a group of scales, but also demonstrating the layering of structures in the preservation.
	LEFT: Another instance showing the underside of the scales, including layering, and in addition, a patch of phosphatized tissue (fiber bundles) on the left side of the photo.   RIGHT: This specimen preserves a patch of scales, showing the central keels in some areas, plus layering and soft tissue remains. Additional photos at higher resolution and using scanning electron microscope (SEM) technology are included in our publication published on November 16, 2011 in PLoS ONE.

So, are keeled scales a holdover from the mosasaur's terrestrial ancestors, or an adaptation to more efficient swimming? At this point, the answer is simply that we don't know. LEFT: This 30 cm Garter snake (Thamnophis sirtalis) has keeled scales that are roughly the same size and shape as those of the 5 m Ectenosaurus specimen shown above.

REFERENCES:

Bell, G.L. Jr. 1993. A phylogenetic revision of Mosasauroidea, unpublished Ph.D. dissertation, The University of Texas at Austin, 293 pp.

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, 501 pages.

Cope, E.D. 1875. The Vertebrata of the Cretaceous formations of the West. Report, U. S. Geological Survey Territories (Hayden). 2:302 p, 57 pls.

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 Academy Science, Transactions 104(1-2):56-75.

Everhart, M.J. 2002. New data on cranial measurements and body length of the mosasaur, Tylosaurus nepaeolicus (Squamata; Mosasauridae), from the Niobrara Formation of western Kansas. Kansas Academy of Science, Transactions 105(1-2):33-43.

Everhart, M.J. 2004. Late Cretaceous interaction between predators and prey. Evidence of feeding by two species of shark on a mosasaur. PalArch, vertebrate palaeontology series 1(1):1-7.

Everhart, M.J. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 322 pp.

Geist, N.R., Carpenter, S., and Stewart, J.D. 2002. Chemical and morphological analysis of soft tissue preservation in a mosasaur. Journal of Vertebrate Paleontology 22(Supplement to 3):57A.

Lane, H. H. 1946. A survey of the fossil vertebrates of Kansas, Part III, The Reptiles, Kansas Academy Science, Transactions 49(3):289-332, 7 figs.

Lindgren, J., Caldwell, M.W. and Jagt, J.W.M. 2008. New data on the postcranial anatomy of the California mosasaur Plotosaurus bennisoni (Camp, 1942) (Upper Cretaceous: Maastrichtian), and the taxonomic status of P. tuckeri (Camp, 1942). Journal of Vertebrate Paleontology 28(4):1043-1054.

Lindgren, J., Alwmark, C., Caldwell, M.W. and Fiorillo, A.R. 2009. Skin of the Cretaceous mosasaur Plotosaurus: implications for aquatic adaptations in giant marine reptiles. The Royal Society, Biological Letters, published online 8 April 2009.

Lindgren, J., Caldwell, M.W., Konishi, T. and Chiappe, L.M. 2010. Convergent evolution in aquatic tetrapods: insights from an exceptional fossil mosasaur. PLoS ONE.

Lindgren, J., Everhart, M.J. and Caldwell, M.W. 2011. Three-dimensionally preserved integument reveals hydrodynamic adaptations in the extinct marine lizard Ectenosaurus (Reptilia, Mosasauridae). PLoS ONE.

Merriam, J.C. 1894. Ueber die Pythonomorphen der Kansas-Kreide. Palaeontographica, 41:1- 39, 4 pls. (in German)

Polcyn, M.J. and Everhart, M.J. 2008. Description and phylogenetic analysis of a new species of Selmasaurus (Mosasauridae: Plioplatecarpinae) from the Niobrara Chalk of western Kansas. pp. 13-28 in Everhart, M.J. (ed.), Proceedings of the Second Mosasaur Meeting, Fort Hays Studies Special Issue 3, Fort Hays State University, Hays, Kansas.

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

Schumacher, B.A. 1993. Biostratigraphy of Mosasauridae (Squamata, Varanoidea) from the Smoky Hill Chalk Member, Niobrara Chalk (Upper Cretaceous) of Western Kansas, Unpub. Masters Thesis, Fort Hays State University, 68 pp.

Snow, F.H. 1878a. On the dermal covering of a mosasauroid reptile. Kansas Academy of Science, Transactions 6:54-58, Fig. 1-2.

Valerio, K. 2008. Anatomy, biostratigraphy, paleoecology, and systematics of Ectenosaurus clidastoides (Squamata, Mosasauridae). Unpublished Masters thesis, Fort Hays State University, 119 pp.

Williston, S.W. 1898a. Editorial Notes. Kansas University Quarterly 7(4):235.

Williston, S.W. 1898b. Mosasaurs. The University Geological Survey of Kansas, Part V. 4:81-347, pls. 10-72.