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Globidens dakotensis - A Rare, Shell Crushing Mosasaur from the Pierre Shale (Late Cretaceous) of Western Kansas

Copyright ?2000-2010 by Mike Everhart

Updated 06/17/2010

 

 

 

 

LEFT: "Globidens feeding on clams" -Copyright ?Dan Varner; used with permission of Dan Varner

Referemce:

Everhart, M.J. 2008. Rare occurrence of a Globidens sp. (Reptilia; Mosasauridae) dentary in the Sharon Springs Member of the Pierre Shale (Middle Campanian) of Western Kansas. p.  23-29 in Farley G. H. and Choate, J.R. (eds.), Unlocking the Unknown; Papers Honoring Dr. Richard Zakrzewski, , Fort Hays Studies, Special Issue No. 2, 153 p., Fort Hays State University, Hays, KS.

Also, Jim Martin, South Dakota School of Mines and Technology, has described a third species of Globidens from the DeGrey Member of the Pierre Shale in central South Dakota. The new species, Globidens schurmanni nov. sp. (Martin, 2007) is also the most complete (and youngest) known specimen, and includes the skull, most of the vertebral column and partial limbs. In his comparison of known specimens, Martin interpreted the Kansas dentary as G. dakotensis.

Martin, J. E. 2007. A new species of the durophagous mosasaur, Globidens (Squamata: Mosasauridae) from the Late Cretaceous Pierre Shale Group of central South Dakota, USA. Pages 167-176 in Martin, J. E. and Parris D. C. (eds.), The Geology and Paleontology of the Late Cretaceous Marine Deposits of the Dakotas. Geological Society of America, Special Paper 427.

Also, just published (2010):

Polcyn, M.J., Jacobs, L.L., Schulp, A.S. and Mateus, O. 2010. The North African Mosasaur Globidens phosphaticus from the Maastrichtian of Angola. Historical Biology 22(1?):175-185.

Globidens is a highly derived genus of mosasaurs (Bell, 1997; Bell and Polcyn, 2005) that reached cosmopolitan (world-wide) distribution during Campanian and Maastrichtian time. Globidens remains typically consist only of isolated specimens of the characteristically round teeth.

The earliest known tooth attributable to a Globidens-type mosasaur was discovered near Maastricht in the Netherlands and figured by Faujas de Saint-Fond (1799, pl. 18, fig. 5).  Another species, G. fraasi, was described by Dollo (1913) from a right dentary collected near Maastricht in the Netherlands. The teeth, however, were laterally compressed and distinctly different from Globidens, and Dollo (1924) subsequently changed the genus name to Compressidens. However, that name was pre-occupied and was revised to Carinodens by Thurmond (1969). Erica von Huene (1935) also described and figured a Globidens-like tooth (G. timorensis) from East Timor in the East Indies.

GLOBY-04a.jpg (30692 bytes) LEFT: A view of the head of Globidens dakotensis adapted from Russell Hawley's pen and ink drawing.

Prior to Martin (2007 - above), only 2 species had been described on the basis of skeletal material (G. alabamaensis Gilmore, 1912 and G. alabamaensis Russell, 1975). However, dentarys are not present with either of these two holotype specimens.

In early 1995, Pete Bussen, a retired rancher and experienced paleontologist from Wallace, Kansas, was prospecting for fossils in the Sharon Springs member of the Pierre Shale near McAllaster Buttes, Logan County, Kansas. The dark gray shale exposure is about a mile north of the locality where, in 1867, Dr. Theophilus H. Turner found and collected what eventually became E. D. Cope's infamous and professionally embarrassing "head-on-the-wrong-end" Elasmosaurus platyurus (Cope, 1868) plesiosaur.

The land that Pete now walked on had already produced the remains of a large plesiosaur, several mosasaurs and a concretion filled with Baculites. As he moved along the side of a steep gully, Pete noticed a large chunk of bone protruding from the shale. By its general appearance, it appeared to be the lower jaw (dentary) of a mosasaur but something was wrong with the teeth. Instead of being sharp, conical spikes for seizing and tearing flesh, the teeth were round and bulbous. The only mosasaurs that he knew of that had bulbous or globular teeth were a rare and unusual genus called Globidens.   The genus had never been collected in Kansas. Pete collected the large piece of the jaw that was exposed, but noted that another piece remained buried deeper in the shale. 

LEFT: When we returned to the site in April, 1995, I placed the posterior portion of the dentary back into the exposure where it fit perfectly with the piece that was still in the shale. I dug out the anterior end of the dentary, but was disappointed not to see any other visible remains. One thing that I noted immediately was that the teeth on anterior of the dentary were shaped differently... more like rounded pegs, than "marbles."

RIGHT: I enlarged the excavation but didn't locate any additional remains. If they had been there originally, they may have eroded out long ago, washed down the gully and lost.

gilmorea.jpg (20929 bytes) Plate 39 from Gilmore (1912): Lateral view of the left maxilla of Globidens alabamaensis (Type specimen) in the United States National Museum (USNM 6527).
gilmoreb.jpg (18777 bytes) Plate 40 from Gilmore (1912): Oblique, medial view of dental border of the left maxilla of Globidens alabamaensis (USNM  6527.
map1a.jpg (28088 bytes) Although the isolated, round teeth had been found in many marine deposits around the world, the first Globidens to be described (G. alabamaensis, Gilmore, 1912) was found in the Mooreville Chalk of Alabama. Another species, Globidens dakotensis (Russell, 1975), was discovered in the Pierre Shale of South Dakota. A third, and very complete Globidens skeleton (including stomach contents) was found in 1993 in South Dakota but has only recently been prepared and described.

LEFT: Map of North America during the Late Cretaceous (Campanian) showing approximate localities of Globidens specimens: 1) Holotype of Globidens alabamaensis, Mooreville Chalk, central Alabama; 2) Holotype of G. dakotensis, Sharon Springs Member, Pierre Shale, western South Dakota; 3) SDSMT specimen (Globidens schurmanni nov. sp.) from the DeGrey Member of the Pierre Shale, central South Dakota; 4) FHSM VP-13828, Sharon Springs Member, Pierre Shale, western Kansas; 5) Undescribed Globidens material from the Ozan Formation, east Texas. (Base map adapted from Carpenter, 1990).

Pete Bussen realized that he had just found the first evidence that Globidens had lived in the Western Interior Sea that covered Kansas millions of years ago. Looking around, he scanned the area for other evidence but found only a few small bone scraps.   Thinking that the jaw represented a piece of a still buried and hopefully more complete fossil, Pete called me and offered me the specimen to dig. When we returned to the site later in the spring, however, the only piece to be found was the distal end of the lower jaw, containing four peg-like teeth. After I removed several cubic yards of shale to make sure that nothing else remained, I concluded that the rest of the fossil had either eroded out years ago or that the jaw was all that had been preserved at that location.

globy-01.jpg (58520 bytes)

Drawing by Russell Hawley, ? Copyright 2000 by Russell Hawley

When the jaw was cleaned and examined, there were a total of 10 teeth, and empty sockets for three others. The largest of the globular teeth was 3 cm (slightly over an inch) in diameter. The front four teeth differed from the globular back teeth and were shaped more like rounded pegs than marbles. The nearly 14 inch long dentary was the front half of the mosasaur’s lower jaw. It came from a jaw that would have been between 24 and 30 inches in length. Since the lower jaw in mosasaurs approximates the length of the skull, the skull of this Globidens would have been 2 to 2 1/2 feet in length. This, in turn, would have scaled up to an animal that would have been about 20 feet in length.

FHSM VP-13828a.jpg (39329 bytes) LEFT: The right dentary of the Kansas specimen of Globidens dakotensis (FHSM VP-13828) in lateral, dorsal, occlusal and medial views.  Note the differences in shape between the anterior, peg-like teeth and the more posterior ball-like teeth. Numbers represent tooth positions. The large areas between teeth 4 and 6, and  9 and 11 indicate that the teeth in those alveoli had fallen out before preservation. In case of tooth #10, exostitial bone growth around the alveolus indicates some sort of a bone infection prior to the death of the mosasaur. (Scale =10 cm)
FHSM VP-13828-1a.jpg (22119 bytes) LEFT: Anterior teeth of FHSM VP-13828 in lingual view. White circle indicates location of the pit formed by a replacement tooth behind and below the older tooth. Scale bar = 2 cm.

RIGHT: A shed (fallen out) tooth of Globidens sp.   from the phosphates of Morocco in Africa.  The oval scar on the middle tooth in the lower row was caused as the replacement tooth absorbed the root of this tooth. A functional mosasaur tooth, including those of Globidens, would normally have a long, columnar root that is solidly attached to the surrounding bone. As the replacement tooth begins to grow, the root of the old tooth is absorbed, allowing it to fall out when the new tooth is ready to move into the alveolus in the jaw.

Glob-Morocco1a.jpg (18187 bytes)

A review of the literature on Globidens showed that the specimen from Alabama is considered to be the oldest in terms of geologic time (Early Campanian). The first specimen from South Dakota (G. dakotensis) came from approximately the same stratigraphic level in the Pierre Shale as the Kansas specimen (Middle Campanian). Another, undescribed specimen from Texas probably falls between G. alabamaensis and G. dakotensis in age. The latest specimen from South Dakota is apparently the most recent. On the basis of a brief field examination of that material, Jim Martin at the South Dakota School of Mines (personal communication, 1995) determined that the Kansas specimen is not the same species as new new specimen.  Globidens skulls appear to be adapted to stand the stresses of a crushing-type bite and the latest Globidens from South Dakota is even more robust in that regard than the earlier species.

globy-2a.jpg (8610 bytes) The Kansas Globidens was found in the Sharon Springs member of the Pierre Shale (Middle Campanian), just below the contact with the Weskan member. From the stratigraphic evidence, it now appears that this specimen is approximately the same age as Globidens dakotensis. Unfortunately, because the type specimen of G. dakotensis does not have a lower jaw, the lower jaw from Kansas cannot be positively assigned to that or any other species. (Adapted from a pen and ink drawing by Russell Hawley)
Since Kansas was located under the Western Interior Sea between Alabama and Texas on the south and South Dakota to the North, it seems likely that Globidens would have been found here also. However, even with more than 100 years of fossil collecting in Western Kansas by such famous paleontologists as  E. D. Cope, O. C. Marsh, C.H. Sternberg, S.W. Williston, and the many others that followed, no Globidens remains had been reported prior to 1996.

The globular teeth of Globidens are so radically different from the normal teeth associated with mosasaurs that it seems evident that this genus had a completely different life style and food source. A twenty foot long mosasaur weighing a thousand pounds or more could certainly eat whatever it wanted, and even round teeth are capable of killing smaller prey. It is most likely, however, given the adaptations that are apparent in the teeth and skull, that Globidens fed on hard shelled invertebrates captured on the sea bottom. It is likely that mosasaurs such as Prognathodon with their large, conical teeth had pursued shelled prey, such as ammonites or even turtles, for millions of years. Globidens may have been an extreme adaptation to that end.

In October, 1997, I had the opportunity to visit The Field Museum in Chicago during the Society of Vertebrate Paleontology meeting. While there, I was allowed the opportunity (Thanks, Bill!) to examine and photograph the type specimen of Globidens dakotensis that had been described by Dale Russell. The two pictures below show the underside of the skull and a comparison of the right dentary of the Kansas specimen with the maxillary teeth of G. dakotensis. While not scientifically significant at this point, I did make the observation that although the jaw length of both specimens is about the same, the teeth of G. dakotensis are about 50% larger in size. I would guess (with no way of telling for sure) that the Kansas specimen is from a slightly smaller individual compared to the type specimen.

LEFT: A ventral view of of the skull of type specimen of Globidens dakotensis (FMNH PR 846) in the Field Museum, Chicago, IL.

LEFT: A close-up showing the teeth of the right dentary of the Kansas Globidens sp. ((FHSM VP-13828), above) compared with the teeth on the premaxilla and right maxillary of the type specimen of Globidens dakotensis (FMNH PR 846).

Martin (2007) indicated that he believes the Kansas specimen should be identified as Globidens dakotensis.

glob-dak.jpg (109562 bytes) LEFT: Ventral and lateral views of the type specimen of Globidens dakotensis (FMNH PR 846); drawing adapted from Russell, 1975. Skull is approximately 26 inches in length.
GLOBY-05a.jpg (28373 bytes) LEFT: A comparison between the FHSM VP-13828 (Scale bar = 10 cm) and a composite drawing of holotype of "Clidastes intermedius Leidy 1870 (ANSP 9023, 9024) from Pickens County, Alabama (no scale); adapted from Leidy, 1873 (Plate 34, figs. 1 and 2). Note that edentulous tip of the FHSM VP-13828 dentary does not compare favorably with the terminally located tooth on the left dentary of the type specimen of ‘Clidastesintermedius."

The anterior portion of the jaw (ANSP 9023) is from the left dentary and is reversed from Leidy's original figure in this composite drawing. Drawing of FHSM VP-13828 by Russell Hawley.

References:

Dollo, L. 1913. Globidens fraasi, mosasaurien mylodonte nouveau du Maestrichtien (Cr閠ac?sup閞ieur) du Limbourg, et l'閠hologie de la nutrition chez les mosasauriens. Arch. Biol. XXVIII 1913, 609-626, pls. xxiv, xxv. (in French)

Dollo, L. 1924. Globidens alabamaensis mosasaurien Am閞icain retrouv?dans la Craie d'Obourg (S閚onien sup閞ieur) du Hainaut, et les mosasauriens de la Belgique en g閚閞al. Arch. Biol. 34;167-213, pl. V.

Everhart, M.J. 2008. Rare occurrence of a Globidens sp. (Reptilia; Mosasauridae) dentary in the Sharon Springs Member of the Pierre Shale (Middle Campanian) of Western Kansas. p.  23-29 in Farley G. H. and Choate, J.R. (eds.), Unlocking the Unknown; Papers Honoring Dr. Richard Zakrzewski, , Fort Hays Studies, Special Issue No. 2, 153 p., Fort Hays State University, Hays, KS.

Everhart, M. J. and P. A. Everhart. 1996. First report of the shell crushing mosasaur, Globidens sp., from the Sharon Springs Member of the Pierre Shale (upper Cretaceous) of Western Kansas. Kansas Academy of Science, Transactions 15(Abstracts): 17.

Gilmore, Charles W. 1912. A new mosasauroid reptile from the Cretaceous of Alabama, Proceedings U.S. National Museum, 40(1870): 489-484, 3 fig., pl. 39-40  (Description of Globidens alabamaensis type)

Huene, E. von. 1935. Mosasaurier-Z鋒ne von Timor. Centralblatt fur Mineralogie. Geologic und Palaeontologie; in Verbindung mit dens Neuen Jahrbuch fur Mineralogie, Geologie und Palaeontologie. Stuttgart. Abt. B 10 412-416, 3 figs. (in German)

Leidy, J. 1873. Contributions to the extinct vertebrate fauna of the western interior territories. Rept., U.S. Geological Survey Territories (Hayden) 1:358 pp., 37 pls.

Lingham-Soliar, T. 1999. The durophagous mosasaurs (Lepidosauromorpha, Squamata) Globidens and Carinodens from the Upper Cretaceous of Belgium and the Netherlands. Paleontological Journal. 33(6):638-647, translated from the Russian, Paleontologicheski Zhurnal 6:34-43.

Martin, J. E. and J. E. Fox. 2004. Molluscs in the stomach contents of Globidens, a shell crushing mosasaur, from the Late Cretaceous Pierre Shale, Big Bend area of the Missouri River, central South Dakota. Geological Society of America, 2004 Rocky Mountain and Cordilleran Regions Joint Meeting, Abstracts with Programs, 36(4):80.

Martin, J. E. 2007. A new species of the durophagous mosasaur, Globidens (Squamata: Mosasauridae) from the Late Cretaceous Pierre Shale Group of central South Dakota, USA. Pages 167-176 in Martin, J. E. and Parris D. C. (eds.), The Geology and Paleontology of the Late Cretaceous Marine Deposits of the Dakotas. Geological Society of America, Special Paper 427.

Martin, J. E. and Fox, J. E. 2007. Stomach contents of Globidens, a shell-crushing mosasaur (Squamata), from the Late Cretaceous Pierre Shale Group, Big Bend area of the Missouri River, central South Dakota. Pages 167-176 in Martin, J. E. and Parris D. C. (eds.), The Geology and Paleontology of the Late Cretaceous Marine Deposits of the Dakotas. Geological Society of America, Special Paper 427.

Russell, Dale A. 1975. A new species of Globidens from South Dakota. Fieldiana Geology, 33(13): 235-256. (Field Museum of Natural History)

Saint Fond, F. 1799.  Head of the Crocodile p. 59-67 (First published history of Mosasaurus hoffmanni); from "Historie Naturelle de la Montage de Saint-Pierre de Maestricht"; Translated from the French by Jean-Michel Benoit.

Schulp, A.S. 2005. Feeding the mechanical mosasaur: what did Carinodens eat? Netherlands Journal of Geosciences / Geologie en Mijnbouw, 84(3), p. 345-358.

Schulp, A. S., J.W.M. Jagt, F. Fonken. 2004. New material of the mosasaur Carinodens belgicus from the Upper Cretaceous of the Netherlands. Journal of Vertebrate Paleontology 24(3): 744-747.

Thurmond, J. T. 1969. Notes on mosasaurs from Texas. The Texas Journal of Science 21(1):69-79.


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