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Gastroliths associated with plesiosaur remains in the Sharon Springs Member  (Late Cretaceous) of the Pierre Shale, Western Kansas

Copyright © 2000-2012 by Mike Everhart

Last updated 05/04/2012




Figure 1. Gastroliths from KUVP 129744. Scale = 10cm.

An slightly different version of this page was published as: 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.

NOTE: This specimen is redescribed as possible remains of Elasmosaurus platyurus in: Everhart, M. J. 2005. Elasmosaurid remains from the Pierre Shale (Upper Cretaceous) of western Kansas. Possible missing elements of the type specimen of Elasmosaurus platyurus Cope 1868? PalArch 4(3): 19-32. Downloadable here.


ABSTRACT: Field work conducted by the Natural History Museum of the University of Kansas in 1991 recovered 38 gastroliths in association with the incomplete and disarticulated remains of a large plesiosaur (KUVP 129744). The specimen was found in the upper Sharon Springs Member (late Cretaceous) of the Pierre Shale, Logan County, Kansas. The gastroliths are unusually large in size when compared to those documented from other plesiosaur remains, and larger than those associated with the giant sauropod, Seismosaurus. This specimen provides new data in regard to the occurrence and sizes of gastroliths in these extinct marine reptiles.



In 1991, a local rancher recognized plesiosaur bones and rounded pebbles eroding from an exposure of Pierre Shale on a hillside in Logan County, Kansas. He contacted Dr. Larry Martin at the Natural History Museum at the University of Kansas and arrangements were made to conduct an exploratory dig on the site. Two dorsal vertebrae, several ribs, gastralia (belly ribs), and bone fragments were recovered during the dig, along with 38 gastroliths (stomach or gizzard stones). According to Pete Bussen (pers. comm., 1999), at least half of the gastroliths were found in situ, piled together in a small area. Two vertebrae, and several ribs were located near the gastroliths. The bones were reasonably well preserved for Pierre Shale fossils from Kansas and appeared to have been randomly scattered before burial. The remains were exposed above the base of a steep slope, and further digging would have required more resources than were available at the time, so the project was postponed until a later date. Three additional gastroliths were found at the site in 1994.

The dig was completed in 1998 by the Cincinnati Museum of Natural History under a cooperative agreement with the University of Kansas. During the five days spent on site, an additional 18 complete ribs and gastralia were discovered, but no limb material or additional vertebrae were found. The bones were scattered randomly over an area of about 15 m2 (5 m by 3 m) along a southeast-northwest axis. The location of original material was near the southeast corner of the second excavation. Six probable gastroliths or fragments of gastroliths were found on the surface below the site. The taphonomy of the remains found in 1998 suggests that the carcass of the animal had ‘bloated and floated’ for some time and had deteriorated to the point that it was falling apart before finally coming to rest on the sea floor. The relatively small number of gastroliths (47) found associated with the ribs and vertebrae also suggests that portions of the remains may have been deposited elsewhere, or that part of the specimen may have eroded away and been lost before it was discovered. A similar specimen (KUVP 1318) from Ellsworth County that was described by Williston (1893) consisted of a few vertebrae and ribs, and about 125 gastroliths.

Gastroliths have been found in a variety of extant species, including birds and crocodiles. In most birds, the gastroliths are generally considered to aid in processing food prior to digestion whereas in penguins they apparently serve as ballast while the animal is in the water. In extinct marine reptiles, such as plesiosaurs, several functions have been proposed. They may have been; 1) used as ballast to keep the animal properly oriented in the water or to help maintain neutral buoyancy; 2) used to grind up food in a muscular crop; 3) swallowed accidentally as the result of feeding on bottom dwelling prey; or 4) swallowed for the minerals that they contain (geophagy). Since most of the documented gastroliths consist of granite, quartz or other insoluble minerals, however, it is unlikely that geophagy is involved (M. A. Taylor, pers. comm., 1999).

Whatever the actual benefit of these stones to the animals that ingest them, the occurrence of gastroliths in plesiosaurs is well documented and comparisons can be made with several of the reported specimens (Williston, 1893; Brown, 1904; Riggs, 1939; Welles and Bump, 1949; and Darby and Ojakangas, 1980).

Carpenter (1999) and Storrs (1999) recently reviewed North American elasmosaurids. Among other important changes, Carpenter made two species originally identified as Alzadasaurus (A. pembertoni, A. kansasensis) junior synonyms of Styxosaurus snowii. Storrs concluded that "(o)f the several elasmosaurian taxa from the Niobrara all save Styxosaurus snowii (Williston, 1890) are specifically nondiagnostic." The revised usage of Styxosaurus is followed here.


FMNH – Field Museum of Natural History; KUVP – Kansas University (Museum of Natural History), Vertebrate Paleontology; NJSM – New Jersey State Museum; SDSMT – South Dakota School of Mines and Technology


The remains of KUVP 129744 were located in the ‘middle’ or ‘organic-rich shale’ unit of the Sharon Springs Member (Zone of Baculites asperformis, lower Middle Campanian) of the Pierre Shale, Logan County, Kansas (Gill, Cobban, and Shultz, 1972). The middle unit is about 27 m (90 ft.) thick and extends upward to within 3 m (10 ft.) of the contact with the Weskan Member. It is a hard, gray, buttress-weathering shale and contains an abundance of vertebrate fossils. The upper portion of the unit is also characterized by a layer of large septarian limestone concretions that were found above the horizon of the KUVP 129744 remains. Coincidentally, the site is within a mile of the locality of the type specimen of Elasmosaurus platyurus found by Dr. Theophilus Turner in 1868 (Almy, 1987) and described by E.D. Cope. It may also be stratigraphically contemporaneous with two other recent finds of elasmosaurs associated with gastroliths in the same vicinity (D.C. Parris, pers. comm., 1992 and 1995).


A number of authors have discussed the presence of gastroliths in plesiosaur remains from the Western Interior Seaway. In his History of the State of Kansas, Cutler (1883) relates the discovery by Professor B.F. Mudge of a plesiosaur where "between the ribs, in the cavity of the stomach were found well worn, siliceous pebbles, from one-fourth to one-half inch in diameter; aids to digestion similar to those found of some reptiles and birds now existing." S.W. Williston (1903) suggested that gastroliths "may have served as a weight to regulate the specific gravity of the animals or they may have been swallowed accidentally". Brown (1904) disagreed with Williston and indicated that the stones were used for the "breaking up of the food." The common occurrence of gastroliths in both long-necked elasmosaurs, and the relatively short-necked pliosaurs, was described by Williston (1906). Williston (1893) published the first photograph of 16 "pebbles from a plesiosaur stomach" (KUVP 1318). Riggs (1939) described a specimen of Elasmosaurus serpentinus (now Hydralmosaurus serpentinus, FMNH 12009) from the Fort Benton Shale in Montana with 206 gastroliths. Welles and Bump (1949) noted the discovery of 253 gastroliths associated with the remains of a Styxosaurus snowii (formerly Alzadasaurus pembertoni, SDSMT 451) from the Sharon Springs Member of the Pierre Shale in South Dakota. Darby and Ojakangas (1980) described the occurrence of 197 gastroliths from an elasmosaur found in the Bearpaw Shale (Campanian) of Montana. This specimen is currently housed in the Department of Geological Sciences at the University Minnesota Duluth (R. Ojakangas, pers. comm., 1999). D. J. Cicimurri (pers. comm., 1999) found more than 80 gastroliths associated with stomach contents in the remains of a Styxosaurus (?) (NJSM 15435) from the upper Sharon Springs Member (Campanian) of the Pierre Shale in Logan County, Kansas. In contrast to the larger numbers of gastroliths associated with these elasmosaurs, only 47 gastroliths were recovered with KUVP 129744.

The sizes of the gastroliths associated with KUVP 129744 (Fig. 1) are unusually large compared to the gastroliths documented for other plesiosaurs, and for the giant sauropod, Seismosaurus (Gillette, 1990). The largest of the gastroliths from KUVP 129744 weighed 1,490 g compared with 1,060 g for the largest from another elasmosaur (NJSM 15435, D. J. Cicimurri, pers. comm., 1999) from the Pierre Shale of Kansas, and 662 g for the largest gastrolith from a plesiosaur described by Darby and Ojakangas (1980) from the Bearpaw Shale of Montana (Table 1). Even though there were only 47 gastroliths recovered with KUVP 129744, the total weight of the gastroliths was 13,078 g compared to 8,841 g (197 gastroliths) from the Darby and Ojakangas (1980) plesiosaur, and 8,249 g (253 gastroliths) from the Styxosaurus snowii described by Welles and Bump (1949). The five largest gastroliths from KUVP 129744 weighed more than a kilogram each and had a combined weight of 6,130 g.

The size range of gastroliths associated with various specimens provides some interesting contrasts. Williston (1893) reported 125 gastroliths varying in weight from less than a gram to 170 grams in one plesiosaur (KUVP 1318). The smallest stone reported by Darby and Ojakangas (1980) weighed 0.5 g whereas the smallest found by D. J. Cicimurri (pers. comm., 1999) in NJSM 15435 weighed 0.65 g. In contrast, the smallest gastrolith associated with KUVP 129744 weighed 7 g. Although NJSM 15435 had a higher average weight per gastrolith (79 g) than either of the specimen of Darby and Ojakangas (45 g), or the Welles and Bump material (33 g), it also had far fewer gastroliths (80+) than either of these specimens. The average weight (79 g) for the gastroliths from NJSM 15435, however, was much less than that from KUVP 129744 (278 g).

Another common measurement applied to gastroliths is the maximum diameter or length of the long axis (Riggs, 1939; Welles and Bump, 1949; Darby and Ojakangas, 1980; and Gillette, 1990). Taylor (1993) found that most gastroliths from marine tetrapods ranged from 5 mm to 100 mm in maximum length. In contrast, the longest gastrolith from KUVP 129744 is 170 mm long, compared with 151 mm for the longest from NJSM 15435, 128 mm for the longest from the Welles and Bump (1949) specimen, and 114 mm for the longest from the material described by Darby and Ojakangas (1980). However, the longest gastrolith from KUVP 129744 (1,320 g) is not the heaviest stone. The heaviest gastrolith (1,490 g) was the only stone with two dimensions greater than 100 mm (129 x 110 x 58 mm). It is worth noting that all these plesiosaur specimens have gastroliths larger than the largest (95 mm long) associated with the giant sauropod, Seismosaurus (Gillette, 1990). Based on measurements of the diameter of the dorsal vertebrae from these plesiosaur specimens, it is likely that the plesiosaurs were 9 m to 12 m long compared with the estimated 40 m length of Seismosaurus.

Darby and Ojakangas (1980) measured the long, intermediate, and short axes, and computed the shapes and sphericity (j = roundness) of the gastroliths as a method of determining the possible source localities (i.e. river versus beach pebbles) where the gastroliths had been obtained. They determined that river pebbles had a higher degree of sphericity on the average than beach pebbles. From the sphericity of the gastrolith material that was studied, it was concluded that the plesiosaur had probably obtained the stones from river deposited gravel in estuaries feeding into the Western Interior Seaway. The shape and sphericity of the KUVP 129744 gastroliths (mean j = 0.736) were very close to the sphericity (mean j = 0.717) reported by Darby and Ojakangas (1980), indicating that the probable source was gravel deposited by a river.

The lithology of gastroliths varies widely between specimens. Taylor (1993) reported that gastroliths associated with aquatic tetrapods were typically composed of "hard rocks such as quartzite, granite and basalt." Riggs (1939) reported that all 206 stones he examined from FMNH 12009 were granite. Wells and Bump (1949) found that 92% of the gastroliths in SDSM 451 were quartzite. Seventy percent of the gastroliths found by Darby and Ojakangas (1980) were gray quartzite and 14% were chert. D. J. Cicimurri (pers. comm., 1999) found that most of the NJSM 15435 gastroliths were composed of Precambrian Sioux pink quartzite and probably originated from the eastern shore of the seaway. "Hundreds of greatly abraded, very smooth and polished stones" were found within the scattered vertebrae of a large shark (KUVP 68979) reported by Moodie (1912). Shimada (1997) also described this specimen and concluded that the shark had ingested the "polished pebbles of black chert (?)" while feeding on a plesiosaur. My examination of KUVP 68979 indicated that most of the 124 gastroliths probably originated from the same lithographic source.

In contrast, the KUVP 129744 gastroliths appear to have come from a wider variety of sources. Since there were no known sources of this type of material in the central portion of the Western Interior Seaway, they must have originated hundreds of miles from where the remains were found. Williston (1903) concluded that most of "the pebbles had been obtained from sea beaches bordering the Black Hills", but that some of them were a red quartzite that appeared to be identical to boulders found in glacial deposits from near Sioux City, Iowa. While Williston was mistaken about the geologic age of the Black Hills uplift, the distance to the nearest source of red quartzite in Iowa is over 700 km (450 mi.). This suggests that plesiosaurs were capable of traveling long distances. Welles and Bump (1949) contended that the source of the gastroliths in SDSM 451 could not be determined with any certainty, but that the plesiosaur was "...many scores of miles away from any shoreline at the time of death." In any case, the sources of the gastroliths associated with KUVP 129744 were not within the mid-ocean deposits that made up the Pierre Shale formation.

In virtually all cases, however, gastroliths are smooth and well rounded. Some exhibit a high degree of polish. Others appear dull or waxy. The surfaces of many gastroliths from the Pierre Shale appear to be coated by a thin film of iron-stained clay from the weathering of the shale (Darby and Ojakangas, 1980). Gillette (1990) stated that the gastroliths of Seismosaurus are more polished than river stones or beach stones." Likewise, the KUVP 129744 gastroliths have a surface patina and smooth texture that distinguishes them from similar sizes and kinds of stones found in river gravel in Kansas, or the river worn rocks found in the overlying Ogallala formation (Tertiary). While most of the stones were oval shaped, even the more angular ones worn to the point that all edges were rounded. It seems apparent that these gastroliths must have been inside the crop of the animal for an extended period of time to have been polished to this degree.

It has been suggested that gastroliths served as ballast for these marine reptiles (Williston, 1903; Darby and Ojakangas, 1980; and Taylor, 1993, 1994). However, the combined weight of gastroliths in any of the examined specimens appears to be insignificant when compared to the weight of the animal itself. An estimate based on scaling up the amount of water displaced by a 33 cm elasmosaur model (Alexander, 1989) suggests a live weight of about 2,800 kg (6,100 lb.) for a 9 m plesiosaur, and raises the question of what, if any, effect that the 13 kg (29 lb.) of gastroliths from KUVP 129744 would have as ballast. Doubling the weight of the gastroliths in this specimen to account for the possibility that a large percentage of the original material was not found with the remains still does not produce an amount greater than one percent of the estimated weight of the animal.

The much smaller total weights of gastroliths found inside relatively complete and undisturbed plesiosaur remains (Riggs, 1939; Wells and Bump, 1949; Darby and Ojakangas, 1980; D. J. Cicimurri, pers. comm., 1999) argues that these stones would have had little or no effect on the buoyancy of those animals. Brown (1904) does suggest that, in dead plesiosaurs, "the weight of these stones would have been too great to have been contained by the weakened tissues and they would be lost before the animal reached its final resting place. This may well explain the absence of stones in some cases."

Taylor (1993) noted that gastroliths are denser and thus are a more energy efficient method of controlling buoyancy than bone, enabling the animal to avoid some of the metabolic cost of depositing more bone as it grows. Taylor’s conclusion that these stones "can be eaten or vomited to change buoyancy quickly" may not be applicable to marine reptiles such as elasmosaurs who have unusually long necks, and which apparently lived and fed in mid-ocean hundreds of miles from the sources of their gastroliths. The physics of buoyancy in marine animals is explained more completely in Taylor (1994) and is beyond the scope of this paper.

The decomposition of large vertebrates in marine environments was thoroughly discussed by Schäfer (1972). Although most of his conclusions were drawn from the observation of marine mammals, some predictions can be made regarding the manner in which a plesiosaur carcass might decay under similar conditions. Schwimmer (1997) applied his "Bloat-and-Float-With-Scavenging" Model to the occurrence of dinosaur remains in marine deposits in the eastern United States as a means of explaining the occurrence of isolated limb elements and vertebrae. A similar model may help to explain the wide variations found in the number and sizes of gastroliths associated with elasmosaur remains.

The following description is proposed as a likely scenario for the ‘’bloating and floating" of a dead elasmosaur based on the analysis of marine mammals by Schäfer (1972). Under normal conditions, a reasonably intact plesiosaur carcass would eventually float as the gases from decomposition built up inside the abdominal cavity. The pressure from these gases would force the limbs, neck, and tail upward into approximately horizontal attitudes, providing tempting targets for scavenging by sharks. Early in the process, the lower jaw would loosen and drop away from the skull and then the skull itself would fall away from the neck as the ligaments holding it to the vertebral column deteriorated. This is consistent with the scarcity of skulls associated with plesiosaur skeletons found in the Western Interior Seaway. In elasmosaurs, the long heavy neck may have broken off in large pieces or been shed one vertebra at a time. Pressure inside the body cavity would have continued to rise, while the connective tissues holding together the dorsal vertebrae and the rib cage, with its heavy belly ribs (gastralia), would begin to fail. After a period of time, the carcass would became a floating ‘bag of bones’ (Schäfer, 1972). Gastroliths and loose ribs/gastralia pressed downward against the deteriorating outer layers of muscle and skin at the lowest point of the abdomen. Eventually, the abdomen would have been ruptured by scavengers, decay or even the weight of the gastroliths (Brown, 1904). If the body wall failed explosively where the weight was the greatest, some or all of the gastroliths and loose bones in the abdomen would be released to scatter across the sea floor. If the gases were released more slowly, and the gastroliths were retained inside the intact stomach or crop of the plesiosaur, the remainder of the carcass could sink to the bottom and be preserved more or less intact.

The fragmentary nature of KUVP 129744 precludes the identification of the remains below family level (Plesiosauroidea: Elasmosauridae). The remains of both Elasmosaurus and Styxosaurus have been found in the upper portion of the Sharon Springs Member of the Pierre Shale in Kansas. The type specimen of Elasmosaurus platyurus, described by E. D. Cope, was found within a mile of the KUVP 129744 site (Storrs, 1999). A large elasmosaur tentatively identified as Styxosaurus (NJSM 15435) was removed by the New Jersey State Museum (Parris, pers. comm., 1993) from the same horizon several miles to the southwest. Another probable specimen of Styxosaurus was recovered from a site about a mile to the northeast in 1999 by the Cincinnati Museum of Natural History (G. W. Storrs, pers. comm., 1999).

129744a2.jpg (10228 bytes) The dorsal vertebrae of KUVP 129744 are comparable (98 mm) in size with those of the 10 m Thalassomedon on display at the Denver Museum of Natural History (K. Carpenter, pers. comm., 1999). The large number of ribs and gastralia, along with the heavy gastroliths suggest that the gas filled carcass ruptured suddenly and spilled a portion of its contents in a relatively small area. Although some material may have been lost to erosion, the location of the gastroliths in contact with one another makes it highly probable that the stones were still contained within the intact stomach or crop when the abdomen ruptured. The remaining ribs, vertebrae and limb material may have drifted further before finally sinking to the bottom. 129744b2.jpg (9399 bytes)


KUVP 129744 provides additional data pertaining to the size of gastroliths in plesiosaurs, but provides no conclusive evidence to resolve the question of the actual function they served in the living animal. Although they represent the largest total weight of gastroliths documented in any animal to date, the relative weight of these gastroliths compared to the estimated weight of the living animal casts some doubt on their use as ballast. The purpose of gastroliths in plesiosaurs remains a mystery.


I thank Jerome (Pete) Bussen for his donation of this specimen to the Museum of Natural History at the University of Kansas, and for sharing his knowledge of the Pierre Shale and other locality information. Dr. David Parris of the New Jersey State Museum, Dr. Larry Martin of the Natural History Museum at The University of Kansas, and Dr. Glenn Storrs of the Cincinnati Museum of Natural History provided the opportunity and encouragement to work with this specimen and other plesiosaur gastrolith material. Dr. Richard Zakrzewski, and Dr. Michael Taylor reviewed the manuscript and provided constructive assistance. Dr. Richard Ojakangas provided unpublished data on the specimen in the Department of Geology at the University of Minnesota (Darby and Ojakangas, 1980). Christopher Whittle gave valuable insights into the occurrence and nature of gastroliths in general, and David Cicimurri generously shared data from his analysis of the stomach contents of another Kansas plesiosaur specimen recovered by the New Jersey State Museum. I would also like to acknowledge the assistance of Ben Creisler, Barry Kazmer, David Lewis, Carina Marshall, Angie Paquette and Oliver Wing who helped with proofreading and providing access to reference material.

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Williston, S. W. 1898. Editorial Notes. Kan. Univ. Quar. 7(4):235. (The dorsal fringe on mosasaurs)

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

Williston, S. W.,

1904. The stomach stones of the plesiosaurs. Science (new series) 22:565.

Williston, S. W. 1906. North American plesiosaurs: Elasmosaurus, Cimoliasaurus, and Polycotylus. American Journal of Science 4(21):221-236.

Williston, S. W., 1914. Water reptiles of the past and present. Chicago Univ. Press. 251 pp. (Free, downloadable .pdf version by the Arment Biological Press)

Table 1: A summary of data on gastroliths associated with late Cretaceous elasmosaurid plesiosaurs from Kansas, South Dakota and Montana.

Specimen Identification Number of Gastroliths Maximum    Length Maximum Weight Average    Weight Total   Weight
KUVP 129744         47 170 mm 1490 g 313 g 13078 g
Styxosaurus  sp. (1)
NJSM 15435 80 151 mm 1060 g 79 g 6300 g
Cicimurri, pers. comm., 1999
Styxosaurus snowii (1)
SDSM 451 253 128 mm 580 g 33 g 8249 g
Welles and Bump, 1949
Styxosaurus sp. (1)
University of Minnesota 197 114 mm 662 g 45 g 8841 g
Darby and Ojakangas, 1980
Hydralmosaurus serpentinus
FMNH 12009 206 102 mm 417 g   N/A   N/A
Riggs, 1939
Elasmosaur (2)
KUVP 1318 125 68 mm 170 g   N/A    N/A
Williston, 1893
Shark (3)
KUVP 68979 124 72 mm   N/A   N/A   N/A
Moodie, 1914; Shimada, 1997

(1) See Carpenter (1999) for revisions to Cretaceous plesiosaur systematics.

(2) The original account by Williston (1903) indicated 125 gastroliths

(3) From the stomach contents of a large lamniform shark (Cretoxyrhina mantelli) that may have fed on a plesiosaur shortly before death (Shimada, 1997) This count may not be complete since the gastroliths are still in the original matrix and some smaller ones may be hidden. Weights are not available.

How much did an elasmosaur weigh?

The weight of an elasmosaur may be estimated by a method developed by R. McNeil Alexander (1989, see above), where the amount of water displaced of a model plesiosaur is used to compute the mass of a real plesiosaur. In the case shown below, the Carnegie Museum model of Elasmosaurus was used to estimate the weight several sizes of living plesiosaurs. Baby elasmosaurs were probably not much longer than about one meter in length (3.2 feet) at birth and weighed about 4 kg (8.2 pounds).  A very large adult, the size of the type specimen of Elasmosaurus platyurus (14 m or 45 ft), would have weighed over 10,000 kg or more than 11 tons.  By comparison, a modern gray whale can reach lengths over 45 feet and weigh more than 35 tons.  The difference is in the long, thin  neck of the elasmosaur... more than half the length of the body.   

Specimen Length (meters) Weight (kilograms) Length (feet) Weight (pounds)
A baby elasmosaur 1 4 3.2 8.2
2 41 6.6 90
3 103 9.8 228
4 244 13.1 538
5 476 16.4 1050
6 823 19.7 1814
7 1307 23 2881
8 1951 26.2 4301
9 2800 29.5 6173
Styxosaurus snowii NJSM 15435 10 3811 32.8 8403
11 5073 36.1 11184
12 6586 39.4 14520
13 8374 42.7 18461
Type of Elasmosaurus platyurus 14 10459 45.9 23000 (11.5 tons)

Gastroliths from other specimens from the Western Interior Seaway and elsewhere.

129744ca.jpg (3623 bytes) Most of the gastroliths found with a partial elasmosaur skeleton by staff of the Natural History Museum at the University of Kansas (KUVP-129744) in 1991 in Logan County, Kansas. The dig on the remains was completed by the Cincinnati Museum in 1998.
129744aa.jpg (2349 bytes) The heaviest of the gastroliths in this specimen, this rounded stone weighed 3.3 pounds (1490 gm) and was 129 mm long.
129744ba.jpg (3332 bytes) The longest of the stones was 170 mm in length and weighed 2.9 lb. (1320 gm)
ku-1991a.jpg (3051 bytes) Three more "probable" gastroliths found at the dig site in 1994.  Since there was less than 50 gastroliths found in situ with this dis-articulated specimen, it is likely that many more of the stones had eroded out years ago.
ku68979i.jpg (3087 bytes) An unusual specimen (KUVP-68979) in the Natural History Museum at the University of Kansas.  First reported by Moodie (1912), this specimen consists of 41 vertebrae of a large shark (Cretoxyrhina mantelli) mixed with more than 120 mostly black, well polished gastroliths. 
ku68979e.jpg (3232 bytes) It is likely that the shark fed on a plesiosaur shortly before it died, leaving the indigestible gastroliths mixed with its own cartilaginous vertebrae.
ku68979d.jpg (3670 bytes) A closer view of the vertebrae and gastroliths.   Based on the size of these vertebrae, the shark would have been between 5 and 6 meters in length when alive.
ku68979f.jpg (2924 bytes) An extreme close up of one vertebra and associated black 'chert' gastroliths.  This specimen was also discussed by Shimada (1997) as evidence of Cretoxyrhina mantelli feeding on plesiosaurs.
ku68979l.jpg (3190 bytes) Another detail from the area near the middle of the specimen, showing the many small gastroliths that were mixed in with the larger sizes.
ku1318aa.jpg (2736 bytes) A collection of about 88 gastroliths that were found associated with Kansas plesiosaur material (KUVP 1318). This specimen was original described by S.W. Williston in 1903. (Click here for a 1903 picture of the same specimen)
ku1318ba.jpg (3759 bytes) A closer look at some of the larger stones from KUVP 1318.  The scale is 6 inches (15 cm) and the largest stones are just over 60 mm in length.  Many of the stones were mottled gray in color and obviously came from the same source.
d&o-01a.jpg (5378 bytes) One of the front paddles of the plesiosaur described by Darby and Ojakangas (1980).  Some of the 197 gastroliths associated with this specimen are visible in the center of the picture.
d&o-02a.jpg (4191 bytes) Looking at the same paddle, with a broken propodial in the fore ground. Gastroliths are visible to the left of the rock hammer.   Children added for scale.
d&o-03a.jpg (4049 bytes) The pile of 'rocks' found associated with this plesiosaur (8.8 kg - 19.4 pounds).   The largest stones were about 11 cm (4.3 inches) long.
sdsmt16a.jpg (3903 bytes) A portion of the 253 gastroliths associated with the remains of the Alzadasaurus pembertoni (Styxosaurus snowii) described by Welles and Bump (1949).  See more pictures here.
gastro3a.jpg (3618 bytes) Part of the thousands of small stones from an elasmosaur specimen found on an island off the coast of Antarctica. (See a webpage on Antarctica fossils here)
vp13919t.jpg (4153 bytes) A collection of probable 'gastroliths' (FHSM VP-13919) from the lower  (late Coniacian) Smoky Hill Chalk, Gove County, Kansas.  These stones were not associated with any vertebrate remains, so their identification as gastroliths is conjectural.  They appear to be quartzite, a mineral which is not found in the chalk.   It is possible that they spilled from the abdomen of a floating carcass of a plesiosaur that was being fed upon by scavengers. (A closer view is HERE)
nj15435c.jpg (11228 bytes) In 2002, I traveled to the New Jersey State Museum in Trenton, New Jersey and had an opportunity to photograph the complete set of gastroliths from the NJSM 15435 Styxosaurus specimen for the first time. The picture at left shows the extreme range of sizes of gastroliths encountered in the stomach contents of this elasmosaur. Note the size of the smallest stone found on the right end of the 3rd row.   The two gastroliths marked (A) appear to be agates. Click HERE for a closer view of these two stones. The red-orange coloring of the gastroliths is due to surface staining by iron oxides.
UN1195gastros1a.jpg (31232 bytes) This is a picture of the more than 240 gastroliths (stomach stones) found associated with the above plesiosaur remains by George Sternberg.  The largest stone measured 79 x 57 x 28 mm and the total weight of the gastroliths was 2.2 kg.   At least two Squalicorax teeth were curated with the specimen and are included with the gastroliths (Circled). One interesting thing about the gastroliths was that they apparently originated from several distinct locations (Note the tan colored stones in the picture).
p-mudgea.jpg (15751 bytes) The picture at left was published in Williston (1903) - North American Plesiosaurs - and shows the more than 200 gastroliths associated with a plesiosaur called Plesiosaurus mudgei (KUVP 1305) from the Lower Cretaceous (Albian) Kiowa Shale, Clark Co., KS. It was collected by C. N. Gould in 1893 and named by Cragin (1894).


NEW: The story of the discovery of Elasmosaurus platyurus Cope 1868

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

  RECENT PAPER: Plesiosaur Stomach Contents and Gastroliths from the Pierre Shale (Middle Campanian) of Kansas

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

The 1999 Cincinnati Museum Plesiosaur Dig

About Plesiosaurs

About Pliosaurs

Plesiosaur References: A listing of publications related to plesiosaurs

A list of references in my library about mosasaurs and plesiosaurs

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

Plesiosauria Translation and Pronunciation Guide

Barry Kazmer's Plesiosaur Paleontology Page