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Mosasaurs from the Museum of Geology

South Dakota School of Mines and Technology

Copyright 2000-2008 by Mike Everhart

Last updated 03/14/08

The Museum of Geology at the South Dakota School of Mines has an outstanding mount of a 29 foot long mosasaur originally identified as Mosasaurus conodon (shown above).  Like just about all mosasaur mounts, it is extremely difficult to capture the specimen in one photograph without losing much of the detail.  The museum store does sell a very well done poster featuring this specimen.  This specimen (SDSMT 452)  is was found in the Pierre Shale (Campanian) near the spillway of Elm Lake, Brown County, South Dakota.  It was cited and extensively figured in Dale Russell's 1967 benchmark publication (Systematics and Morphology of American Mosasaurs), and is the subject of a new paper currently in preparation. 

The museum also houses many other vertebrate and invertebrate fossil specimens, as well as an extensive mineral collection.  The collection includes other mosasaur material, the type specimen of the elasmosaur, Alzadasaurus pembertoni (now Styxosaurus snowii, see Carpenter, 1999), several dinosaurs, and Pleistocene mammals.  It's open year-around (except holidays), and is certainly worth a visit if you are in the Black Hills area of South Dakota.   Admission is free

The museum also offers several field paleontology courses for credit during the Spring and Summer months.  For more information, you can call 1-800-544-8162, ext. 2467, or write: Museum of Geology, 501 E. Saint Joseph St., Rapid City, SD, 57701.  Their email address is:

This web page will, of course, feature the mosasaur material on display as well as some pictures of mosasaur specimens not seen by the public.    So kick off your shoes and get ready to enjoy a virtual journey into the late Cretaceous seas that once covered South Dakota, and the rest of the Midwest.

sd452-1a.jpg (3545 bytes) The right side of the skull of a mosasaur (SDSMT 452) identified as  Mosasaurus conodon at the Museum of Geology. This skull is about 4 feet long, from the nose to the back of the lower jaw. If you are interested in the names of the bones of a mosasaur skull, particularly the lower jaw, CLICK HERE.
sd452-2a.jpg (4483 bytes) The left side of the same skull.  Mosasaurus conodon is closely related to the first mosasaur ever found: Mosasaurus hoffmanniIt is also the only kind of a mosasaur  that I have ever found in the Pierre Shale.
sd452-3a.jpg (3177 bytes) Possibly the last thing that many of this mosasaur's prey ever saw.  This view inside the skull shows the two rows of pterygoid teeth at the back of the mouth.  These served to help hold the prey while the mosasaur was swallowing it.... a very useful adaptation to living in the ocean, and for modern snakes.  For a close up of the pterygoid teeth, CLICK HERE.
sd452-4a.jpg (3921 bytes) This picture shows the back of the right side of the skull.  The distinctive quadrate bone, which serves as the hinge point for the lower jaw and supports the ear drum is in the center of  the picture.  For a labeled version of this picture, CLICK HERE.
sd452-11.jpg (3418 bytes) sd452-13.jpg (4589 bytes) A series of upper right side skull photographs added 9/23/00 sd452-15.jpg (4142 bytes) sd452-17.jpg (5247 bytes)
sd452-19.jpg (2984 bytes) An overview of the skeleton of Mosasaurus conodon. While swimming the front and rear limbs would have been held against the body except when needed for steering.
sd452-7a.jpg (3447 bytes) The right front limb (paddle) of SDSMT 452 showing the attachment to the shoulder. The limbs of Mosasaurus were very robust compared to those of earlier mosasaurs such as Tylosaurus.
sd452-8a.jpg (2792 bytes) A closer view of the right front paddle.  Mosasaurus limb and paddle bones have very distinct shapes. For a picture with the limb bones labeled, CLICK HERE
sd452-6a.jpg (3204 bytes) The left rear limb (paddle) and tail of Mosasaurus conodon. For a picture with the limb bones labeled, CLICK HERE.  The tail is about half the length of the body.
sd452-9a.jpg (3690 bytes) A look at the the back end of the same mosasaur.  Mosasaurs swam using an undulating, side to side movement of their tail, much like that of a modern snake.
sd452-21.jpg (4065 bytes) The author shown for the sake of scale as compared to a 29 foot long mosasaur.

..........and what did mosasaurs eat?

sdstom1a.jpg (3382 bytes) This plaster jacket (SDSMT 10439) contains the vertebrae, pelvic and limb bones of a large mosasaur (Tylosaurus) as well as the preserved remains of the animals (a fish, a bird and a smaller mosasaur)  that the Tylosaur ate shortly before it died. To see this picture with the Tylosaurus bones labeled, CLICK HERE.  To see a colored drawing that shows the stomach contents, CLICK HERE. (Copyright SDSMT Museum of Geology)
sdstom2a.jpg (4706 bytes) This jumble of bones is the last remains (mostly vertebrae) of a mosasaur called Clidastes. The large bone in the center is part of the hips (the ileum) of the larger Tylosaurus. While the Tylosaurus was probably about 10 m in length, the Clidastes was probably less than 4 m in length. The stomach contents were part of a nearly complete Tylosaurus specimen found in the summer of 1978 in the Gammon Ferruginous Member of the Pierre Shale.
sd10439a.jpg (4002 bytes) This close up shows several of the bones from the anterior end of the Clidastes, including a quadrate, a possible pterygoid bone and several cervical vertebrae.  The interpretation is made that the Clidastes was swallowed head first.
sdstom3a.jpg (4610 bytes) This picture shows the bones of a large, flightless bird called Hesperornis found within the stomach contents. The birds swam in the Cretaceous seas much like modern penguins, probably feeding on smaller fish and squid. To see a picture of a Tylosaurus chasing a Hesperornis, CLICK HERE.

For more information about the above specimen, see:  Martin, James E. and Bjork, Phillip R., 1987, Gastric Residues Associated with a Mosasaur from the Late Cretaceous (Campanian) Pierre Shale in South Dakota, Dakoterra, Vol. 3, pp. 68-72


sdplat1a.jpg (3923 bytes) The skull of a Platecarpus (SDSMT 30139) from the Pierre Shale near Edgemont, South Dakota. Platecarpus was a very common mosasaur in the Niobrara chalk and early Pierre Shale.
sdsm-moa.jpg (4531 bytes) The underside of a very complete and nearly three dimensional skull of Prognathodon overtoni (SDSMT 3393), from the Virgin Creek Member of the Pierre Shale, Shannon County, South Dakota.  Prognathodon is a relatively rare mosasaur and may be related to GlobidensTo go to the Prognathodon overtoni page, CLICK HERE   (New 07/29/00)

.............and from the collections in storage


sdhain1a.jpg (5221 bytes) The skull of a huge Prognathodon overtoni from the Pierre Shale called the "Dewey County Mosasaur".  It was collected from an island in the Missouri River about 1990 by Jim Martin and Dan Varner. (There's a great story behind this one... ask Dan sometime).  Note the scale at the top of the picture is 10 cm or about 4 inches.  CLICK HERE for  a different view.
sdclid1a.jpg (4305 bytes) A very scattered Clidastes propython specimen from the Niobrara chalk of South Dakota.  The various bones are labeled in the larger picture (unnumbered, from the WHO collection). Scale is 10 cm.
sdclid2a.jpg (3592 bytes) A close-up view of the long, slender (and very toothy) lower jaws of Clidastes propython.
sdclid3a.jpg (3189 bytes) The underside of the frontal bone from the skull of Clidastes propython. This bone is found on the top of the skull, between the eyes of the mosasaur.
sdhain2a.jpg (2900 bytes) Most of another very large skull of a tylosaurine mosasaur (probably Hainosaurus) from the Sharon Springs Member of the Pierre Shale, south of Rapid City, S. D.  In this jacket, from right to left,   the premaxilla, nasals, frontal and part of the parietal are visible. Scale = 10 cm.
sdquad1a.jpg (3343 bytes) The quadrates of the above Hainosaurus.   Like the skull, these bones are truly huge compared to those of most other mosasaurs.  Scale = 10 cm (about 4 inches) sdquad2a.jpg (3389 bytes)
sdtootha.jpg (3296 bytes) One of the large teeth found with this specimen. For two other views of the same tooth, CLICK HERE, and CLICK HERE. Scale is in cm.
sdplio1a.jpg (4173 bytes) One of the front limbs of a Plioplatecarpus (SDSMT 40597). These limb bones are much more robust than those of a typical tylosaur and suggests that some of the later mosasaurs were using their front limbs much more than the earlier mosasaurs for directional control or underwater 'flying'.
sdplio2a.jpg (3013 bytes) The top of the skull of another Plioplatecarpus (SDSMT 40596) from the Gregory Member of the Pierre Shale, Buffalo County, South Dakota.   The various bones and other features are labeled in the larger version.
sdplat2a.jpg (3994 bytes) A small, unnumbered mosasaur skull from the Pierre Shale in the collection of  the Museum of Geology.  The scattered elements of this skull probably came from a juvenile Platecarpus.  To see the elements of the skull labeled, CLICK HERE.

This is only a small portion of the extensive collection of fossil specimens at the Museum of Geology.... the exhibits also include:

sdples0a.jpg (5787 bytes) ............ a large plesiosaur (Styxosaurus snowii).  Click here to go to the Museum of Geology  Styxosaurus snowii page. (Updated  09/25/2000)
sdtoxy1a.jpg (2311 bytes) .... several marine turtle skulls (Toxochelys browni)
sdxiph1a.jpg (5773 bytes) ..... a large fish (Xiphactinus audax), about 12 feet long
sdpach1a.jpg (5444 bytes) .... a smaller fish, preserved in 3-D (probably Apsopelix anglicus), about 2 feet long
sdptyc1a.jpg (5022 bytes) ... a jaw plate from the shell crushing shark, Ptychodus mortoni.
sdcrab1a.jpg (3287 bytes) ... fossil crabs from Mississippi (Avetilmessus grapsoideus)
sdcrin1a.jpg (4371 bytes) ..... colonial crinoids (Uintacrinus socialis) from the Smoky Hill chalk of Kansas.  See close-ups of several individuals from the Sternberg Museum: HERE, HERE and HERE.
sdbacu1a.jpg (4266 bytes) ... a section of a baculite (Baculites compressus) from the Pierre shale.  Note the distinctive sutures.
sdammo1a.jpg (2635 bytes) ... one of many ammonites (Prionocyclus wyomingensis) on display
sdammo2a.jpg (2198 bytes) .... another large ammonite (Collignoniceras woollgari)
sdtyrana.jpg (3441 bytes) ... and last but not least, a couple of dinosaurs, including this Tyrannosaurus rex skull.

I hope you have enjoyed this short tour of the Museum of Geology and it's collections.  Jim Martin and the rest of the crew at the School of Mines have a great collection and one of the best paleontology field school programs in the country.  In addition to learning basic paleontology skills, many recent discoveries, including a 'mother' mosasaur with babies,   a nearly complete Globidens mosasaur and a huge marine turtle have been the result of finds made by students during the Field School.    If you are at all interested in experiencing real paleontology work in the field, South Dakota is a great place to do it.  I know... I've been there...   done that: digging on a Mosasaurus in 1996; and finding a Mosasaurus in 1998.


Bell, G. L. Jr., J. E. Martin, D. C. Parris, and B. S. Grandstaff, 1994. Mosasaurus dekayi in the upper Cretaceous (Campanian-Maastrichtian) marine deposits of South Dakota and New Jersey. Jour. Vert. Paleon. 14(Supplement to 3):17A.

Bell, G. L. Jr., M. A. Sheldon, J. P. Lamb and J. E. Martin. 1996. The first direct evidence of live birth in Mosasauridae (Squamata): Exceptional preservation in Cretaceous Pierre Shale of South Dakota. Journ. Vert. Paleon. 16(supplement to 3):21A.

Bell, G. L. Jr., and J. P. VonLoh, 1998. New Records of Turonian Mosasauroids from the Western United States, Fossil Vertebrates of the Niobrara Formation in South Dakota, Dakoterra 5:15-28

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

Martin, J. E. and P. R. Bjork, 1987. Gastric Residues Associated with a Mosasaur from the Late Cretaceous (Campanian) Pierre Shale in South Dakota, Dakoterra, Vol. 3, pp. 68-72.

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., Vol. 67, pp. 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., Vol. 67, pp. 76-79

Martin, J. E. and J. D. Stewart, 1993. Late Cretaceous Selachians and associated marine vertebrates from the Dakota Rose Quarry, Grant County, South Dakota. Proc. S. D. Acad. Sci. 72:241-248.

Martin, J. E. 1994, A baby plesiosaur from the late Cretaceous Pierre Shale, Fall River County, South Dakota. Jour. Vert. Paleon. 14(Supplement to 3):35-36A.

Martin, J. E. 1994. Gastric residues in marine reptiles from the late Cretaceous Pierre Shale in South Dakota: Their bearing on extinction. Jour. Vert. Paleon. 14(Supplement to 3):36A.

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

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

Russell, D. A. 1975, A New Species of Globidens from South Dakota, Fieldiana Geology, Volume 33, No. 13, Field Museum of Natural History

Schumacher, B. A. and J. E. Martin, 1993, First Definitive Record of the Mosasaur Tylosaurus proriger from the Niobrara Formation (upper Cretaceous), South Dakota, Proc. S.D. Acad. Sci., Vol. 72, pp. 235-24

Schumacher, B. A. and D. W. Varner, 1996. Mosasaur caudal anatomy. Jour. Vert. Paleon. 16(supplement to 3):63A

Sheldon, M. A. , G. L Bell, Jr., and J. P. Lamb, 1996. Histological characters in prenatal specimens of the mosasaur, Plioplatecarpus primaevus. Jour. Vert. Paleon. 16(supplement to 3):64A.

VonLoh, J. P. and G. L. Bell Jr., 1998. Fossil Reptiles from the Late Cretaceous Greenhorn Formation (Late Cenomanian-Middle Turonian) of the Black Hills Region, South Dakota, Dakoterra Vol.5, pp. 28-38

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

For more about mosasaurs, visit the Virtual Mosasaur Museum

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