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Styxosaurus snowii

An elasmosaur at the Museum of Geology,

South Dakota School of Mines and Technology

Copyright © 2000-2008 by Mike Everhart

Updated 03/14/2008

sd451-5a.jpg (5200 bytes) This page features the mount of a large (36 feet long) elasmosaur (SDSMT 451) in the collection of  the Museum of Geology at the South Dakota School of Mines and Technology. It was the type specimen of Alzadasaurus pembertoni, discovered near Iona, South Dakota in 1945 but has since been re-identified as "just another" Styxosaurus snowii, albeit the most complete one ever found. The specimen was first described by S. P. Welles and James Bump in 1949 (Alzadasaurus pembertoni, a new elasmosaur from the Upper Cretaceous of South Dakota, Journal of Paleontology, Vol. 23, No. 5, pp. 521-535) and the name was revised to Stysoxaurus by Ken Carpenter (1999). (NOTE: The holotype of Styxosaurus snowii is at the University of Kansas (KUVP 1301), The SDSMT 451 plesiosaur was found with 253 gastroliths (stomach stones) in it's abdomen.  The gastroliths are on display in a case at the museum.  Pictures of a several of these gastroliths are shown below.  If you are interested in learning more about gastroliths in plesiosaurs, CLICK HERE.  For more about plesiosaurs in general, CLICK HERE.  The following pictures were taken in July and September 2000. sd451-6a.jpg (3589 bytes)
sdsmt7a.jpg (2923 bytes) A right side view of the skull of Styxosaurus snowii.  The skull was difficult to photograph because it is about 15 feet above the floor of the museum and is dark brown in color.
sdsmt8a.jpg (3358 bytes) Another view of the right side of the skull showing the first few cervical (neck) vertebrae. For a picture of another skull of Styxosaurus snowii in the Museum of Natural History at the University of Kansas, CLICK HERE.
sd451-1a.jpg (3452 bytes) Slightly different angle... better lighting (added 09/23/00). These pictures were taken while balancing on a long ladder....
sd451-2a.jpg (3227 bytes) Shot from above the skull, showing the upward facing orbit of the right eye.  Many artists have shown elasmosaurs with their heads held high above the water.  Not only was this physically impossible (try it yourself by lifting a long pole out of the water while floating), there was no way that the plesiosaur could see beneath his chin.
sdsmt11a.jpg (2061 bytes) The same shot from further away, showing more of the cervical vertebrae.
sdsmt15a.jpg (3936 bytes) A view of the left side of the skull from below.  Note that the lower jaw hinges from the extreme back of the skull.  The width of the skull at this point was probably an indication of the size of prey that this plesiosaur could swallow.   The long, sharp teeth of plesiosaurs were used primarily to seize and hold prey, and not for cutting or chewing. In spite of being almost forty feet long, this elasmosaur fed on fish that were no larger than 1.5 to 2 feet in length, swallowing them whole.
sd451-3a.jpg (3146 bytes) Another view from below the skull (added 09/23/00)
sdsmt10a.jpg (3667 bytes) A view of the anterior cervical vertebrae. Elasmosaurs such as Styxosaurus had many vertebrae in their elongated necks (The most (71) were found in Elasmosaurus).   In elasmosaurs, the neck was about half the total length of the body.
sdples5a.jpg (4560 bytes) The posterior section of the neck as it transitions into the dorsal vertebrae of the body. The bones making up the shoulders of the specimen are in the lower left corner.
sdsmt12a.jpg (3172 bytes) A 'chest-on' view of Styxosaurus snowii.   The head of the animal is located above the camera.
sd451-4a.jpg (3481 bytes) Looking down on the specimen from above.
sdsmt9a.jpg (4196 bytes) A close up of the posterior cervical vertebrae of Styxosaurus, showing the interlocking processes necessary to support a neck of this length.  Although earlier depictions of elasmosaurs showed a great deal of flexibility in the neck (twisting like a snake), it is more likely that their mobility was somewhat more limited. 
sdsmt13a.jpg (3546 bytes) A view of the shoulder or pectoral region of Styxosaurus. The scapulas and coracoids were enlarged in plesiosaurs and formed an almost solid bony shield under and across the chest.
sdsmt14a.jpg (3689 bytes) The hip or pelvic region of Styxosaurus was constructed very much like the chest of the animal, forming an body plate under the rear quarters of the animal.  Between the front and hind limbs, rows of gastralia (belly ribs)   supported (and protected?) the mid-body area.
sdples6a.jpg (3421 bytes) The right hind limb or paddle of Styxosaurus is an nearly solid mass of leg, ankle and toe bones.  These tightly knitted together bones formed an 'air-foil' that the plesiosaur used in swimming through the water (sub-aqueous flight).  Plesiosaurs moved their paddles in a 'figure-8' motion and   literally 'flew' through the water, much the same a modern seals, sea-lions, and penguins do.
To read a recent paper about large plesiosaur gastroliths from Kansas and see more gastrolith pictures, CLICK HERE.
sdsmt16a.jpg (3903 bytes) sdsmt17a.jpg (3668 bytes) These pictures show some of the 253 gastroliths that were found associated with this specimen. While they may look like a collection of rounded pebbles, they are special because they spent a long time inside the stomach of this elasmosaur. Their use is still uncertain, but I believe that it is probable that they aided in the digestion of the prey (whole fish) swallowed by the plesiosaur.  sdsmt18a.jpg (3956 bytes) sdsmt19a.jpg (4844 bytes)

Below are pictures taken in December, 1999 during my "walk-around" of this impressive mounted specimen.

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Picture 1 is looking at the right front of the chest and right front paddle of the plesiosaur.  The neck is going off to the upper right.   Picture 2 is a view of the right rear paddle and abdomen. Notice the gastralia (belly ribs) that cover (and protect?) the lower portions of the abdomen.   This is one reason why a plesiosaur was described as "a snake drawn through the shell of a turtle"(*).  The long (18') neck disappears to the upper right.    Picture 3 shows the 'south-end of a north-bound plesiosaur' and illustrates the pelvic girdle fairly well. The relatively short tail was probably not used in swimming but may have been used as a rudder. Picture 4 shows the pectoral girdle from the left side.  The objects on the floor are ammonites.

(*) While the source of this quote has been a mystery for a number of years, it was solved by Richard Forrest in September, 2005. Richard found that it was apparently first used in a German publication (Dames, Wilhelm [Barnim]. 1895.  Die Plesiosaurier der süddeutschen Liasformation. Abhandlungen der Königlichen Akademie der Wissenschaften in Berlin (physics-math), pp. 1-83, pls. i-v.  [The plesiosaurs of the Lias Formation of southern Germany]). Quote "...dass man Plesiosaurus mit einer durch einen Schildkrõtenpanzer gezogenen Schlange vegleich ..." which translates as " can compare the Plesiosaurus to a snake threaded through the shell of a turtle.." It is also mentioned in Zarnik (1925), which was written in Serbo-Croat (Zarnik, B.; 1925; Sketologiji plesiosauriija, sa prinosima mehanici kraljeznice u recentnih sauropsida.; Societas Scientiarum Naturalium Croatica, Hrvatskoga Naravoslovno Drestva; 38-39 pp.424-473 (On the ethology of plesiosaurs with contributions to the mechanism of the cervical vertebrae of recent sauropsids) . 
paddlesa.jpg (36218 bytes) Although plesiosaurs evolved from terrestrial reptiles with four legs, the limbs were highly modified into paddles, and lost most of the mobility of the elbow / knee, wrist / ankle and fingers / toes. The bones of the wrist became specialized to the point that they have had to be given different names (no longer carpals or tarsals).

LEFT: A lateral (dorsal) view of the left front and rear limbs of Styxosaurus snowii (SDSMT 451) as adapted from Welles and Bump (1949, pl. 5)  Abbreviations:  Ra = Radius; Ul = Ulna; Ti = Tibia; Fi = Fibula; Re = Radiale; In = Intermedium; Ue = Ulnare; Te = Tibiale; Fe = Fibulare.


Where the elasmosaurs roam.... Prehistoric Times (#53, April, 2002)

On a Plesiosaur dig with The New Jersey State Museum -1991

Completing the dig with the New Jersey State Museum -1992

"We Dug Plesiosaurs" - with the Cincinnati Museum in 1998

The 1999 Cincinnati Museum Plesiosaur Dig

A webpage about Plesiosaurs (Elasmosaurs)

A webpage about Pliosaurs (short-necked plesiosaurs)

Plesiosaur References: A listing of publications related to plesiosaurs

A list of references in my library about mosasaurs and plesiosaurs.

Plesiosauria Translation and Pronunciation Guide

Richard Forrest's listing of plesiosaur specimens and literature

Also, you can visit Ray Ancog's Plesiosaur FAQ Page (Frequently Asked Questions)

REFERENCES (Click here to see a complete listing):

Brown, B., 1904. Stomach Stones and the Food of Plesiosaurs, Science, 20(501):184-185.

Carpenter, K., 1999. Revision of North American Elasmosaurs from the Cretaceous of the Western Interior, Paludicola, 2(2):148-173.

Cicimurri, D. J. and M. J. Everhart, 2001. An elasmosaur with stomach contents and gastroliths from the Pierre Shale (late Cretaceous) of
Kansas. Kansas Acad. Sci. Trans 104(3-4):129-143

Darby, D. G. and Ojakangas, R. W., 1980. Gastroliths from an Upper Cretaceous Plesiosaur. Jour. Paleon.  54(3):548-556.

Everhart, M. J., 2000. Gastroliths associated with plesiosaur remains in the Sharon Springs Member of the Pierre Shale (late Cretaceous), Western Kansas. Kansas Acad. Sci. Trans. 103(1-2):58-69.

Everhart, M. J., 2002. Where the elasmosaurs roam...... Prehistoric Times 53:24-27.

Everhart, M. J.  2003.  First records of plesiosaur remains in the lower Smoky Hill Chalk Member (Upper Coniacian) of the Niobrara Formation in western Kansas. Kansas Academy of Science, Transactions 106(3-4):139-148.

Everhart, M. J.  2004. New data regarding the skull of Dolichorhynchops osborni (Plesiosauroidea: Polycotylidae) from rediscovered photos of the Harvard Museum of Comparative Zoology specimen. Paludicola 4(3):74-80.

Everhart, M.J. 2004. Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the  Niobrara Formation of western Kansas. The Mosasaur 7:41-46.

Everhart, M.J. 2005. Bite marks on an elasmosaur (Sauropterygia; Plesiosauria) paddle from the Niobrara Chalk (Upper Cretaceous) as probable evidence of feeding by the lamniform shark, Cretoxyrhina mantelli. PalArch, Vertebrate paleontology  2(2): 14-24.

Everhart, M.J. 2006. The occurrence of elasmosaurids (Reptilia: Plesiosauria) in the Niobrara Chalk of western Kansas. Paludicola 5(4):170-183.

Everhart, M. J. 2007. Use of archival photographs to rediscover the locality of the Holyrood elasmosaur (  Ellsworth County ,  Kansas ). Kansas Academy of Science, Transactions 110(1/2): 135-143.

Martin, J. E. and Kihm, A. J., 1988. Two Unusual Stratigraphic Occurrences of Plesiosaurs from Late Cretaceous Formations of the Black Hills Area, Wyoming and South Dakota, Proc. S.D. Acad. Sci. 67:73-75.

Martin, J. E. and Kennedy, L. E., 1988. A Plesiosaur from the Late Cretaceous (Campanian) Pierre Shale of South Dakota: A Preliminary Report, Proc. S.D. Acad. Sci. 67:76-79.

Martin, J. E., B. A. Schumacher, D. C. Parris, and B. S. Grandstaff, 1998. Fossil Vertebrates of the Niobrara Formation in South Dakota, Dakoterra 5:39-54.

Riggs, E. S., 1939. A Specimen of Elasmosaurus serpentinus, Field Museum of Natural History, Geology, 6:385-391.

Schumacher, B.A. and M.J. Everhart. 2005. A stratigraphic and taxonomic review of plesiosaurs from the old “Fort Benton Group” of central Kansas: A new assessment of old records. Paludicola 5(2):33-54.

Shuler, E. W., 1950. A new elasmosaur from the Eagle Ford Shale of Texas. Part II. Fondren Science Series V1, #2, 1-33 pp. 26 figs.

Storrs, G. W., 1981. A Review of Occurrences of the Plesiosauria (Reptilia: Sauropterygia) in Texas with Description of New Material, Masters Thesis, The University of Texas at Austin, 226 pages.

Storrs, G. W., 1984. Elasmosaurus platyurus and a page from the Cope-Marsh war. Discovery 17(2):25-27.

Storrs, G. W., 1997. Morphological and Taxonomic Clarification of the Genus Plesiosaurus, pp. 145-190, In Calloway, J. M. and Nicholls, E. L., eds, Ancient Marine Reptiles, Academic Press.

Storrs, G.W., 1999. An Examination of Plesiosauria (Diapsida: Sauropterygia) from the Niobrara Chalk (upper Cretaceous) of Central North America, The University of Kansas Paleontological Contributions, (N. S.), No. 11, 15 pp.

Taylor, M. A., 1981. Plesiosaurs - rigging and ballasting, Nature 290:628-629.

Taylor, M. A., 1986. Lifestyle of plesiosaurs, 1986, Nature 319:179.

Taylor, M. A., 1993. Stomach Stones for feeding or buoyancy? The occurrence and function of gastroliths in marine tetrapods, Phil. Trans. R. Soc. Lond. B 341:163-175.

Taylor, M. A., 1994. Stone, bone or blubber? Buoyancy control strategies in aquatic tetrapods, pp.151-161, In Maddock, L., Bone, Q., and Rayner, J. M. V. (ed.), Mechanics and Physiology of Animal Swimming, Cambridge University Press.

Welles, S. P., 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. University of California Memoirs 13:125-254. figs.1-37., pls.12-29.

Welles, S. P., 1949. A new elasmosaur from the Eagle Ford Shale of Texas, Fondren Science Series, Southern Methodist University, 1:1-28.

Welles, S. P., 1952. A review of the North American Cretaceous elasmosaurs. University of California Publications in Geological Sciences 29:46-144. figs. 1-25.

Welles, S. P. 1953. Jurassic plesiosaur vertebrae from California. Jour. Paleon. 27:743-744, 1fig.

Welles, S. P., 1962. A New Species of Elasmosaur from the Aptian of Columbia and a Review of the Cretaceous Plesiosaurs, University of California Press, Berkeley and Los Angeles.

Welles, S. P., and Bump, James, 1949, Alzadasaurus pembertoni, a new elasmosaur from the Upper Cretaceous of South Dakota, Jour. Paleon. 23(5): 521-535.

Williston, S. W., 1893. An Interesting Food Habit of the Plesiosaurs, Trans. Kansas Acad. Sci. 13:121-122, 1 plate.

Williston, S. W., 1903. North American Plesiosaurs, Field Columbian Museum, Pub. 73, Geological Series, 2(1):1-79, 29 plates.

Williston, S. W., 1906. North American Plesiosaurs: Elasmosaurus, Cimoliasaurus, and Polycotylus, Amer. Jour. Sci. 4(21):221-236.

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