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Copyright ©2001-2013 by Mike Everhart

Last revised 11/10/2013

LEFT: "Brachauchenius and squid" -Copyright © Dan Varner; used with permission of Dan Varner

July 3, 2003 - Translated into French   flag.jpg (870 bytes)

by Jean-Michel Benoit  (Click on flag)

Pliosaurid or Polycotylid?

Cretaceous plesiosaurs have been traditionally divided into two major sub-groups; the long-necked, small headed "elasmosaurs" and the short-necked, larger headed "pliosaurids." For a time, this was convenient for most purposes, but it has become a somewhat arbitrary method of dividing the group since some of the so-called "polycotylids" of the Late Cretaceous may be more closely related to the elasmosaurs. The discussion of the systematics of plesiosaurs, however, is beyond the scope of this article (see Carpenter 1996; and O'Keefe 2001; 2004, 2008  for a further information).

On this this webpage, we will consider the pliosaurids to include the large-headed, short-necked plesiosaurs, such as Kronosaurus and Brachauchenius lucasi that became extinct about the Middle Turonian stage of the Late Cretaceous, along with the polycotylid Trinacromerum bentonianum. Three polycotylids, Polycotylus latipinnis, Dolichorhynchops osborni and D. bonneri, lived during the latter part of the Late Cretaceous in the Western Interior Sea 

For information about plesiosaurs in general, and especially the long necked variety, see the Something About Plesiosaurs webpage. Click here for the latest information on Elasmosaurus platyurus.   For other Oceans of Kansas webpages about plesiosaurs, see: On a dig for the New Jersey State Museum Plesiosaur; Completing the Dig for the New Jersey State Museum Plesiosaur - 1992We Dug Plesiosaurs-1998Cincinnati Museum Plesiosaur Dig in 1999; and the Styxosaurus snowii elasmosaur at the South Dakota School of Mines.   See also Ben Creisler's Plesiosaur Translation and Pronunciation Guide for more information on plesiosaur names and their pronunciation.  

How did plesiosaurs swim?? .... Consider the possibilities here:  PLESIOSAUR SWIMMING --- Animations on the Plesiosauria website by Adam Stuart Smith


Brachauchenius lucasi

The only pliosaurid  officially recognized from Kansas at this time is Brachauchenius lucasi Williston 1903. A few fragmentary specimens suggest one or more other species may have been present. In Kansas, these short-necked pliosaurids are relatively rare, but are represented by two excellent specimens, the largest of which is on exhibit at the Sternberg Museum of Natural History. Also, see the Brachauchenius webpage for more information.


Order Plesiosauria, de Blainville 1835

Superfamily Plesiosauroidea, Welles 1943

Family Brachaucheniidae Williston 1925

Genus Brachauchenius lucasi Williston 1903

vp321a.jpg (8347 bytes) Certainly the largest of the Kansas pliosaurids is Brachauchenius lucasi. The holotype (USNM 4989) was collected from the "Benton Formation" in Ottawa County, Kansas and was described by Samuel Williston in 1903. A second specimen (UNSM 2361) was collected from the Eagle Ford Formation near Austin, Texas, and described by Williston in 1907. The skull of a third specimen (FHSM VP 321, shown here) is more complete and somewhat better preserved. It was collected by George Sternberg in October, 1950, from the Fairport Chalk member of the Carlile Shale, in Russell County, Kansas, and is on display in the Sternberg Museum at Fort Hays State University. This skull is about five feet (152 cm) in length along the mid-line, and must have come from a creature that was truly huge. Additional pictures are HERE.
un50136a.jpg (17662 bytes) LEFT: The partial skull of a Brachauchenius lucasi (UNSM 50136) specimen from an unknown locality in Kansas. Very similar in size and preservation to FHSM VP-321 (above).

RIGHT: A portion of the skull and a jaw with teeth of a Brachauchenius lucasi specimen (UNSM 112437) from Mitchell County discovered in the Graneros Shale during the construction of the Glen Elder Dam. Possibly the oldest known specimen of this species. (Both specimens in the collection of the University of Nebraska State Museum)

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gillet2a.jpg (11833 bytes) LEFT: Photograph (click to enlarge) of a recently discovered skull and lower jaws of a Brachauchenius from the Glen Canyon National Recreation Area in Utah. Skull is slightly less than a meter in length. This picture was part of a poster presentation by David Gillette and Barry Albright at the 2003 Society of Vertebrate Paleontology meeting in St. Paul, MN.
UTAHBRAA.jpg (19339 bytes) LEFT: This a photo of the same Brachauchenius specimen now on exhibit in the John Wesley Powell Memorial Museum in Page, Arizona.  According to Merle Graffam, who is the co-discoverer of the specimen, there are more than ten separate finds of pliosaurids in Utah.  All are from the Tropic Shale (Upper Cenomanian - Lower Turonian) and are about 93 million years old. (Photo by Merle Graffam)
VARNR26b.jpg (19679 bytes) LEFT: Here a giant pliosaur (Brachauchenius lucasi) is about to make lunch of a small turtle similar to Desmatochelys.  Brachauchenius was one of the last of the pliosaurs and made it's final appearance in Kansas during the deposition of the Fairport Chalk Member (middle Turonian) of the Carlile Shale. Dan Varner © painting courtesy of the Museum of Northern Arizona.
VP 13997a.jpg (23024 bytes) LEFT: A portion of the paddle of a very large pliosaur (FHSM VP-13997) from the basal Lincoln Limestone Member of the Greenhorn Limestone (Middle Cenomanian), Russell County, KS.  The bones would have come from a paddle that was about 2 m (6.5 ft) in length, and a Brachauchenius-like pliosaur that was about 25 feet long.
Brachtootha.jpg (24524 bytes) RIGHT: A large pliosaur tooth collected from the upper Dakota Sandstone (Mid-Cenomanian) by Keith Ewell in 2004. The tooth is most likely from Brachauchenius, and if so, would be the earliest report of this genus anywhere.


Both Williston (1907) and Carpenter (1996) suggested that Brachauchenius was closely related to Kronosaurus from the Early Cretaceous of Australia and to the Jurassic pliosaurid, Liopleurodon.

    <td width= According to local sources in Australia, Kronosaurus queenslandicus was discovered by a station owner named Ralph William Haslam Thomas. The remains were dug up by the Harvard expedition after they were shown where it was on his 20,000 acre property "Army Downs" near Hughenden in central Queensland,  Australia. Mr. Thomas apparently had known about a row of large vertebrae poking out of the ground for many years prior to the Harvard expedition. He in turn informed the Harvard team of its existence.  When it was finally dug up, the specimen was shipped to the United States in 86 cases weighing approximately 6 tons. The export permit states that the specimen was transported the SS Canadian Constructor about the 1st of December 1932. (Shaw Studio photograph). Click here for an older black and white photograph.


Shortly after the discovery of Elasmosaurus platyurus by Dr. Theophilus Turner (Cope, 1868) in Pierre Shale of Logan County, Kansas, another "new" kind of plesiosaur was found in the upper Smoky Hill Chalk "about five miles west" of Fort Wallace (Cope, 1871, p. 386). A land agent and part-time fossil hunter named W. E. Webb, discovered the remains of a much smaller plesiosaur that Cope (1869) called Polycotylus latipinnis (USNM 27678) from a pelvic arch and twenty-one vertebrae. The genus name refers to the deep "cupping" of the anterior and posterior surfaces of the vertebrae, a character that was quite different from other plesiosaur vertebrae seen by Cope up until then.

Following Webb's discovery, two other species of short necked plesiosaurs were found in Kansas. One, Trinacromerum, was discovered in the underlying "Fort Benton" Formation, and was much older than Polycotylus. The other, Dolichorhynchops, was also found in the Smoky Hill Chalk and lived at the same time as Polycotylus.

Trinacromerum bentonianum

Trinacromerum bentonianum Cragin 1888 was described from two skulls (USNM 10945 -holotype and USNM 10946 - paratype) found in the (?) Fencepost Limestone member of the Greenhorn Limestone (early Middle Turonian) in Osborne County, Kansas.

Carpenter (1996) assigned both Trinacromerum and Dolichorhynchops to the Polycotylidae.


Order Plesiosauria, de Blainville 1835

Superfamily Plesiosauroidea, Welles 1943

Family Polycotylidae, Cope 1869

Genus Trinacromerum Cragin 1888

Trinacromerum bentonianum Cragin 1888

willtbea.jpg (15875 bytes) The specimen at upper left is the paratype skull (USNM 10946) in ventral view. The drawing shows it as figured in Williston 1908. I had the opportunity to photograph it in the Field Museum of Natural History, Chicago, IL, during my visit there in August, 2002. A larger image of Williston's Fig. 1 is HERE.
us10946c.jpg (11449 bytes) Carpenter (1996) figured the skull of Trinacromerum bentonianum (USNM 10946 - paratype) in more detail than Williston. These figures are from an early draft of the 1996 publication and are copyright © by Kenneth Carpenter; used with permission of Ken Carpenter.

LEFT: Dorsal view

RIGHT: Ventral view

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KUVP5070-1a.jpg (22200 bytes) LEFT: A complete, articulated skull of Trinacromerum bentonianum (KUVP 5070) in right and left lateral views.  The specimen was discovered in December, 1936, during the construction of a road-cut along U.S. 81 Highway, south of Concordia (Cloud County), Kansas.  This specimen was originally described in 1944 by Elmer Riggs and named Trinacromerum willistoni after S. W. Williston. Per Carpenter (1996), the original name is a junior synonym of T. bentonianum. The lower jaw measures 74.5 cm (29 inches).

RIGHT: The distal end of the jaws in right lateral view. The specimen consists of a complete skull with mandible, fifty vertebrae (fifteen cervicals including the atlas-axis), ribs, most of the pectoral girdle, both pubes and the ischia (Riggs, 1944).

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KUVP5070-2a.jpg (22748 bytes) LEFT: The back of the skull of Trinacromerum bentonianum (KUVP 5070) in left lateral view.  Riggs (1944) noted that it occurred "10 feet below the Jetmore Chalk member in beds which, futher west of this area, have been classified as the Hartland Shale member of the Greenhorn Limestone formation. Carpenter (1996) reassigned the specimen to T. bentonianum, and Schumacher and Everhart (2005) reviewed Rigg's locality and stratigraphic information and confirmed the age as Late Cenomanian.

RIGHT: The cranial portion of the skull in right lateral view (top) and the posterior portion of the skull in right lateral view (lower).   

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vp698-1a.jpg (21442 bytes) LEFT: Part of the remains of a large Trinacromerum bentonianum (FHSM VP-698) found by George Dreher in Ellis County, Kansas. The specimen was collected by George Sternberg and M. V. Walker in June, 1956 from the Blue Hill Shale Member of the Carlile Shale and is Middle Turonian in age. The specimen consists of a 3 m (10 ft) string of vertebrae, attached ribs and some limb elements. The axis-atlas vertebrae was included, but the skull was not found. Sternberg's description of this jacket says; "In the articulated column, this section fits between section 2 and 3.  This section contains about 21 continuous vertebrae and a number of ribs. The section is about 50" long and is the widest and largest section in the series. Packages #4 and #5 go with the section, also some loose rock slabs with rib elements."

vp12059x.jpg (18676 bytes) LEFT: A dorsal view of the left humerus of a Trinacromerum bentonianum (FHSM VP-12059) in the Sternberg Museum collection, with an associated Squalicorax falcatus tooth (inset). (Another bone here)

RIGHT: Shark bite marks on both sides of the left coracoid of VP-12059.  (Fairport Chalk, Ellis County, KS)

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esu-plia.jpg (17737 bytes) LEFT: The front paddle of another Trinacromerum bentonianum (ESU 5000) that was found in the 1970s south of Wilson Lake in Russell County.  The locality is at the contact between the Greenhorn Limestone and the Fairport Chalk Member of the Carlile Shale (early Middle Turonian). The paddle is about 1.1 m (43 in.) long

Sadly, however, the rest of the specimen was stolen from the dig site by unknown persons and was never recovered. A single surviving paddle is on exhibit in the Johnston Museum of Geology, Emporia State University, Emporia, Kansas.

As an interesting side note (to me at least), the last known fossils of Trinacromerum bentonianum in Kansas occur in the same rocks (Fairport Chalk and Blue Hill Shale members of the Carlile Shale - Middle Turonian) as the first known remains of mosasaurs.

Polycotylus latipinnis:

"[Cope] also explained, from specimens, the characters of a large, new Plesiosauroid from Kansas, discovered by Wm. E. Webb, of Topeka, which possessed deeply biconcave vertebrae, and anchylosed neural arches, with the zygapophyses directed after the manner usual among vertebrates. The former was thus shown to belong to the true Sauropterygia, and not to the Streptosauria, of which Elasmosaurus was type. Several distal caudals were anchylosed, without chevron bones, and of depressed form, while proximal caudals had anchylosed diapophyses and distinct chevron bones.   The form was regarded as new, and called Polycotylus latipinnis, from the great relative stoutness of the paddle."  E. D. Cope (1869).


Order Plesiosauria, de Blainville 1835

Superfamily Plesiosauroidea, Welles 1943

Family Polycotylidae, Cope 1869

Genus Polycotylus Cope 1869

Polycotylus latipinnis Cope 1869

Polycotylus latipinnis was the second species of plesiosaur found in Kansas. Cope (1875, p. 70) noted that the remains of the type specimen were found by William Webb "about 5 miles WEST of Fort Wallace, on the plains near [the] Smoky Hill River, Kansas, in a yellow Cretaceous limestone." The problem with this locality is that there are no exposures of Smoky Hill Chalk 5 miles west of Fort Wallace. It is likely that the locality is 5 miles east of Fort Wallace in the yellow Smoky Hill Chalk near the Smoky Hill River.  According to O'Keefe (2004), the remains consist of "vertebrae, an ilium, and metapodials at the Smithsonian (USNM 27678) as well as more vertebrae and assorted phalanges housed at the American Museum of Natural History (AMNH 1735).  It is uncertain how the remains became divided among the two museums.

KUVP40002-1a.jpg (41986 bytes) LEFT: A cast of the left rear paddle of Polycotylus latipinnis (KUVP 40002), part of a nearly complete specimen collected from the Pierre Shale of South Dakota in the 1970s.
kuvp591a.jpg (43965 bytes) In 1903, Williston wrote "Some years ago, an excellent specimen of a paddle of a plesiosaur (KUVP 5916) in the exhibit of the University of Kansas Museum of Natural History) belonging in all probability to Polycotylus latipinnis Cope was collected by Mr. George R. Allman of Wallace, Kansas, from the upper Niobrara Chalk of the Smoky Hill River, east of Fort Wallace." Click here for more recent photo

"The bones of the paddle were, for the most part, found in their natural relations, but were separated in the collection of them. The radius and ulna of second paddle, together with some of the smaller bones showed weathering, and doubtless had been picked up from the surface. It has required but little trouble  to fit into their natural relations all the bones except the most of the phalanges, which, presenting no lateral surfaces for articulation, could only be located from their other characters."

Williston (1906, p. 233) noted that the "genus Polycotylus, described by Cope in 1870 from a number of mutilated vertebrae and fragments of the podial bones has remained hitherto much of a problem, and its characters have been very generally misunderstood. Fortunately, there is an excellent specimen in the Yale Museum (No. 1125) collected many years ago by the late Professor Marsh in the vicinity of Fort Wallace, Kansas, from the Niobrara chalk, which I believe can be referred with certainty to the type species P. latipinnis Cope. That it belongs to the genus Polycotylus is beyond dispute, the vertebrae agreeing quite with the type as they do.  This species seems to be the most common one of the order in the Kansas chalk, and is represented by several other specimens in the Yale Museum and by several specimens in the University of Kansas collection."

Williston (1906, p. 234) went on to re-describe the species from what became the "paratype" specimen - YPM 1125:

"Polycotylus. Teeth rather slender, with numerous well marked ridges. Face with slender beak. Cervical vertebrae twenty-six in number; dorsals twenty-eight or twenty-nine, inclusive of three pectorals;  all short and all of nearly uniform length. Chevrons articulating in a deep concavity; all the vertebrae, and especially the cervicals, rather deeply concave, and with a broad articular rim. Pectoral girdle with distinct clavicles, interclavicles, and interclavicular foramen; the scapulae not contiguous in the middle. Coracoid with a long anterior projection, united in the middle, back of the interglenoid bar, to the posterior margin; a foramen on each side, back of interglenoid thickening. Ischia elongated. Paddles with four epipodial bones all much broader than long." 

polyvera.jpg (20271 bytes) LEFT: Two cervical vertebrae of Polycotylus latipinnis (YPM 1125) from the side and behind; and a dorsal vertebrae from the front. (Williston 1914, Fig. 34)

RIGHT: A probable humerus and femur of Polycotylus latipinnis (FFHM 1972.126.12f) in the collection of the Fick Fossil and History Museum, Oakley, KS.

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Dolichorhynchops osborni:



Note that these plesiosaurs were featured in the 2007 National Geographic IMAX movie "Sea Monsters" and in my book, "Sea Monsters - Prehistoric Creatures of the Deep."

Polycotylus latipinnis and Dolichorhynchops osborni were the "end of the line" so far as the short-necked polycotylids were concerned.   Polycotylus is known only from fragmentary material, mostly from the Smoky Hill Chalk, and more recently from Alabama (O'Keefe, 2004). The first two examples of Dolichorhynchops osborni Williston 1903 were found by George Sternberg in the Smoky Hill Chalk in Logan County, KS. Dolichorhynchops persists into the Campanian and possibly the Maastrichtian (See Adams, 1997).

A brief description of the skull of Dolichorhynchops osborni as provided by Williston (1903:14) is repeated here: "Head elongate, the facial region much attenuated; teeth nearly uniform in size, small; prefrontal and postfrontal bones not joined; parietals extending into a high crest; supraoccipital bones separated; internal nares small, included between the vomer and palatine only; palatines broadly separated throughout; a large vacuity between the pterygoids anteriorly; quadrate process of pterygoids short."


Order Plesiosauria, de Blainville 1835

Superfamily Plesiosauroidea, Welles 1943

Family Polycotylidae, Cope 1869

Genus Dolichorhynchops Williston 1902

Dolichorhynchops osborni Williston 1902

plio-sml.jpg (23818 bytes) The mounted holotype of Dolichorhynchops osborni (KUVP 1300) at the University of Kansas Museum of Natural History, with a replica of the the skull. Click for larger version of this picture and click here for the 1946 version of this exhibit, showing the original skull of the specimen.
ku-tri3a.jpg (3950 bytes) ku-tri2a.jpg (4421 bytes) LEFT and RIGHT: Several closer views of the holotype specimen at the University of Kansas. ku-tri1a.jpg (3619 bytes) ku-tri4a.jpg (4524 bytes)
1300-3a.jpg (5532 bytes) vp13001a.jpg (4851 bytes) LEFT and RIGHT: These photos show a drawing published by Williston (1903) and the skull of the specimen in the KU collection.  vp13002a.jpg (4115 bytes) vp13005a.jpg (4588 bytes)

mcz5086y.jpg (13425 bytes) Rare pictures of a juvenile skull of Dolichorhynchops osborni found by George F. Sternberg in 1926 in the Smoky Hill Chalk of Logan County, Kansas. George also had the distinction of finding the type specimen (KUVP 1300, above) as a teenager in 1900.

See Everhart (2004) for the history of this specimen. Photos by George F. Sternberg (Smithsonian archives).

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1064-5a.jpg (10733 bytes) LEFT/ RIGHT: After being offered for sale to the Smithsonian and the American Museum of Natural History, the specimen was mounted in plaster with just the right side of the skull showing, and acquired by the Museum of Comparative Zoology  (MCZ) at Harvard University, Cambridge, MA. The specimen was curated as MCZ 1064. Photo by George F. Sternberg (about 1926) - from the archives of the Sternberg Museum. 1064-4a.jpg (28578 bytes)
mcz1064k.jpg (10610 bytes) Unfortunately, the plaster mount hides most of the important details of the skull from view. It was removed from the exhibit in the 1950s. The drawing at left of the specimen was published recently by F. Robin O'Keefe and is used with permission.

(See: O'Keefe, F. R., 2001. A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia). Acta Zool. Fennica 213:1-63.) 

Also: O'Keefe, F. R. 2004. On the cranial anatomy of the polycotylid plesiosaurs, including new material of Polycotylus latipinnis Cope, from Alabama. Journal of Vertebrate Paleontology 24(2):326-340.

1064-1a.jpg (11865 bytes) These recent pictures of MCZ-1064 were provided by Charles R. Schaff, Curatorial Associate of the Museum of Comparative Zoology and are used with his permission.

LEFT: The right side of the skull, and parts of the lower jaws

RIGHT: This photo shows the elements of the right rear paddle.  The femur is at the lower left, and an ileum (part of the pelvis) is at the upper right. 

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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.

ABSTRACT: The Dolichorhynchops osborni specimen (MCZ 1064) in the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, was the second of only three nearly complete specimens of this species ever recovered from the Smoky Hill Chalk Member of the Niobrara Chalk Formation (Upper Cretaceous). The remains were discovered by George F. Sternberg in 1926 and later acquired by Harvard. Sternberg apparently mounted the skull in a block of plaster that obscures many important details and limits its usefulness. Recently re-discovered photos of the skull, included in correspondence sent by Sternberg to Charles W. Gilmore in 1926, provide an excellent record of the original appearance of this rare specimen. Measurements taken from these photographs are compared with those published of other specimens of this species.

vp-404a.jpg (12433 bytes) LEFT: A third, nearly complete specimen (FHSM VP 404, shown here in right lateral view and below in 1960 vintage pictures) was found in Logan County by Marion Bonner in October, 1955, and is currently on display in the Sternberg Museum.

View from the left side is HERE. The specimen was described by Marion Bonner's son, Orville, in his 1964 Masters thesis.  See also Sternberg and Walker (1957).   In George F. Sternberg's records, there is a handwritten note that says. "Plesiosaur  Trinacromerum osborni presented 12-12-55 by the collector, M.C. Bonner and son Orville, Leoti, Kans. to the College Museum."

FHSM VP404 skulla.jpg (37711 bytes) LEFT: A 1950s photo of the skull of Dolichorhynchops osborni in right lateral view. The skull is long and narrow. It is also lightly constructed and is almost always found severely crushed. The skull of this specimen in the Sternberg Museum is about 16 inches long (51.3 cm), and probably came from a fairly young individual. The skull of a larger individual (KUVP 40001) found in Wyoming was over 3 feet (98 cm) long. Photo from the Sternberg Museum of Natural History.

NEW (12/2007) - Detailed photographs of skull.

VP-404-Sacruma.jpg (17208 bytes) LEFT: This photo shows a left lateral view of the pelvis (pelvic girdle) and a portion of the posterior dorsal vertebrae of the FHSM VP-404 specimen. Note that the pelvic girdle is only attached to the vertebral column by two slender shafts of bone.. the ilia...
Plesiosaur paddles (podials) are composed of five 'fingers' with as many as fifteen bones per digit. The upper bone of the podial is the humerus (front) or femur (rear) and the lower limb bones (and wrist or ankle) are greatly reduced in number and function. These elements were held tightly together to form a rigid, wing shaped paddle or 'airfoil'. By moving these paddles in a coordinated 'figure-eight' pattern, the animal was more or less able to 'fly' swiftly though the water, much like a modern penguin, in pursuit of it's prey.
s-plio2a.jpg (2632 bytes) Dolichorhynchops and other plesiosaurs ate fish that they caught in their long, narrow jaws. Looking ungainly on land in this museum exhibit, they were masters of underwater 'flight' in the ocean, using their two sets of aerodynamic paddles to fly through the water.   Another view of Dolichorhynchops © 2001by Russell Hawley. For more information about Locomotion and Respiration in Marine Air Breathing Vertebrates check out Richard Cowen's excellent, technical paper.

Below are two sets of drawings of polycotylid skulls from the draft of a paper by Kenneth Carpenter (Denver Museum of Natural History)......"A Review of Some Short Necked Plesiosaurs from the Cretaceous of North America". These drawings are copyright © by Kenneth Carpenter, and used with the permission of Kenneth Carpenter.

Left lateral view of the skull of Dolichorhynchops osborni (FHSM VP 404) in the Sternberg Museum, Fort Hays State University, Hays, KS. Click on picture to see a dorsal and ventral view of the skull, and a dorsal view of the mandible (110 kb .jpg file). Scale = 10cm. Copyright © by Kenneth Carpenter.

NEW (12/2007) - Detailed photographs of skull.

LEFT:  A left latero-dorsal view of the skull of a juvenile Dolichorhynchops osborni (UCM 35059) at the University of Colorado Museum at Boulder, CO.  Click on skull to see dorsal and ventral views (84 kb .jpg file). Scale = 10 cm. Copyright © by Kenneth Carpenter.

The specimen consists of a partial skeleton of a young individual from the Sharon Springs member of the Pierre Shale in Niobrara County, Wyoming, and provides the most complete skull of a juvenile member of this species. 

When I visited the Field Museum in Chicago in 2002, I photographed another specimen of Dolichorhynchops osborni (UNSM 50133) that was on loan from the University of Nebraska State Museum. The pictures below show the top of the skull and the back of the skull. A close-up of the anterior portion of the jaws is shown here

UNSM50133a.jpg (35544 bytes) LEFT: UNSM 50133 comes from the Sharon Springs Member of the Pierre Shale in the Hat Creek drainage of Fall River County, South Dakota. The skull measures 61.8 cm in length.

RIGHT: UNSM 50133 in rear view.

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UNSM 55810a.jpg (26043 bytes) LEFT: One of the smallest known skulls of Dolichorhynchops osborni (UNSM 55810).

RIGHT: The anterior end of the left dentary in lateral view.

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Two of the largest polycotylid specimens known from the Western Interior Sea (KUVP 40001 and 40002) were collected in the Sharon Springs Member of the Pierre Shale in South Dakota and Wyoming. KUVP 40002 is a nearly complete skeleton, lacking most of the skull.

KU40001-1a.jpg (21322 bytes) LEFT: A left lateral view of the reconstructed skull of Dolichorhynchops bonneri (KUVP 40001) from the Pierre Shale of South Dakota.  The new species was described by O'Keefe in 2008.

RIGHT: The same skull in posterior view.


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KU40001-2a.jpg (11546 bytes) LEFT: An oblique, left posterio-lateral view of the reconstructed skull (KUVP 40001).

RIGHT: The skull as mounted on the reconstructed skeleton of Dolichorhynchops bonneri in the Rocky Mountain Dinosaur Research Center.

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LEFT: One of the two polycotylid propodials (USNM 9468) recovered from inside the rib cage of a Tylosaurus proriger from the chalk of Logan County, Kansas (either a humerus or femur) by Charles Sternberg and sons. Note partially digested appearance. See Everhart, M. J. 2003.


RIGHT: The second of two propodials recovered by Sternberg, even more severely damaged by stomach acids.




Note that the discovery of this specimen was the focus of the 2007 National Geographic IMAX film - Sea Monsters

cmc7055x.jpg (14502 bytes) LEFT: The femur (16 in / 40 cm long) of a very large Dolichorhynchops osborni that was collected in 1992 from a concretion near the top of the Sharon Springs Member of the Pierre Shale in Logan County. My wife, Pam, discovered this specimen while the rest of us were working on the New Jersey State Museum Styxosaurus snowii.  She had asked our friend, Pete Bussen, "What does a plesiosaur fossil look like in the shale?"  They walked up the hill for a look, and within ten minutes, she picked up a small, sun-bleached paddle bone. She had found her first plesiosaur. It was coming out of a large septarian concretion near the top of the Sharon Springs Member of the Pierre Shale. Of course, finding was the easy part; getting it out the concretion was a lot more difficult (and is the source of my 'flying shovel' story).

 Unfortunately, the concretion had shattered most of the bones and made a difficult puzzle out of the specimen. It is incomplete and will never be an exhibit specimen, but it is certainly an excellent example of how big these marine reptiles could be. Ken Carpenter (Denver Museum of Nature and Science) identified the remains for me in 1994. In 1999, we donated the specimen (CMC VP-7055) to the Cincinnati Museum Center. I had the opportunity to take these pictures in February, 2003.

cmc7055w.jpg (10504 bytes) LEFT: This photo shows the nearly round head of an upper limb bone (femur) and part of the hip, still held together by the matrix of the concretion. 

RIGHT: Centra of five caudal (tail) vertebrae.

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vp-404-a.jpg (14171 bytes) LEFT: A recent picture of the long, toothy skull of FHSM VP-404 on exhibit in the Sternberg Museum of Natural History.  This plesiosaur was definitely a fish-eater. (Age is Early Campanian)

RIGHT: A skeletal reconstruction of Dolichorhynchops osborni in the ancient seas exhibit at the Smithsonian Institution (USNM V-419645). The specimen was collected in 1977 from Bearpaw Shale the Custer Battlefield National Park in Montana. (Age is Campanian)

usnmpola.jpg (14137 bytes)
viennaa.jpg (11708 bytes) LEFT: This composite skeleton of Dolichorhynchops osborni is one of the exhibits in the Vienna Museum of Natural History in Vienna Austria.  It was assembled from various sets of partial remains found in the chalk of western Kansas. The skull is a replica.


Unfortunately, plesiosaurs are few and far between in the Smoky Hill chalk. What we do find occasionally are the scattered pieces of plesiosaur carcasses that had been torn apart during scavenging by other predators. The bones are unusually solid and heavy, but some still bear the marks of the teeth that severed them from the plesiosaur's body.

An 'as found' view of a lonely, sub-adult plesiosaur propodial (LACMNH 148920) eroding out on the surface of the Smoky Hill chalk in Gove County, Kansas. From the serrated bite marks that were found on the bone and the fact that no other plesiosaur material was found in the vicinity, it seems apparent that this readily 'detachable' piece was torn away by scavenging sharks before (Squalicorax) being dropped to the sea bottom. (See Everhart, 2003)
Another 'detached' plesiosaur podial (length about 24 inches). This specimen is on exhibit in the Fick Fossil and History Museum in Oakley, Kansas. The deep bite marks on the upper portion of the bone attest to the violence of the scavenging and the size of the scavenger (a large Late Cretaceous shark, Cretoxyrhina mantelli).  See Everhart (2005).
This specimen represents the only plesiosaur skull (FHSM VP-13966) remains that we have ever found in the chalk (Late Coniacian - about 86 mya). The bone fragments were scattered over a large area and are mostly unrecognizable. They remained unidentified until we showed them to J.D. Stewart of the Los Angeles County Museum of Natural History. The two semi-circular shapes are the hinge points for the lower jaw of the plesiosaur, indicating another possible 'detachable' part that was carried off by a shark. (See Everhart, 2003)
A mosasaur's worst nightmare....when the hunter becomes the hunted.  A Brachauchenius-sized pliosaurid attacks a much smaller mosasaur....not much of a fight. This encounter could only have occurred during the Turonian, about 90 mya, because that was the only time that big pliosaurids and mosasaurs lived together in the Western Interior Sea. This image is copyright © by Dan Varner, and may not be used in any form without his written permission. 
juvpoda.jpg (3002 bytes) An upper limb bone or propodial of a young plesiosaur (species indeterminate) found in the Bluffport Marl Member of the Demopolis Formation (Campanian) in Clay County, Mississippi by Lynn Harrell, Jr. Length is about 8 inches / 20.5 cm.  In juvenile plesiosaurs, the limb bones were growing rapidly and the joints were composed primarily of cartilage.  Note the lack of articular surfaces on the ends of this bone compared to some of the adult limb bones shown above.
1988-25a.jpg (5494 bytes) This a picture of the upper half of a partially digested, juvenile plesiosaur propodial (FHSM VP-139632) which was found near the base of the Smoky Hill Chalk (Late Coniacian) in Ellis County, Kansas by the author in 1988. Unfortunately, the rest of the bone (and the animal itself) was no where to be found. While plesiosaurs in general are not well documented from the lower Smoky Hill Chalk, there are occasional remains that show they were there in small numbers. (See Everhart, 2003), and that they were scavenged by sharks.
tateplia.jpg (3104 bytes) The Tate Museum in Casper, Wyoming, has a copy of a nearly complete paddle from a what must have been a huge Jurassic pliosaurid (Megalneusaurus rex). It was one of the largest marine predators that ever lived.  Found about 1898 by W. C. Knight (University of Wyoming) in Natrona County, Wyoming, this pliosaurid may have been 40 feet long and weighed as much as 10 tons. The articulated paddle measures 7.25 feet (2.209 m). tatepl2a.jpg (3203 bytes)
polycota.jpg (7442 bytes) Trinacromerum bentonianum was an earlier Cretaceous polycotylid that lived in the Western Interior Sea during Cenomanian - Turonian time.  It  was quite similar in size and shape to Dolichorhynchops. LEFT:   Paleo-life art by Carl Buell. Copyright © by, and used with the permission of Carl Buell. The original version of this picture was done by Carl for Discover Magazine for a story done on this article: Sato, T. and K. Tanabe, 1998. Cretaceous plesiosaurs ate ammonites, Nature, 394:629-630.

Also, polycotylid artwork by Peter Von ShollyRussell HawleyDoug Henderson, Dan Varner and S. W. Williston.   All are copyright © by the respective artist and may not be reproduced without permission of the artist and Oceans of Kansas Paleontology.


The following comments about 'pliosaurids' and their possible origin was written by Darren Naish and is reprinted here with his permission.

'Pliosaur' is an ambiguous term that, in the past, has been applied to any plesiosaur with a shortish neck and large head. One group of such animals, the mid-->Upper Cretaceous polycotylids, are very distinct from other 'pliosaurs' and are almost certainly related to elasmosaurids (Bakker 1993 and Carpenter 1995, 1997). True pliosaurids, in contrast, are primitive in the plesiosaur family tree as testified by their complete set of mandibular bones, and out-group to all other plesiosaurs (clade Plesiosauroidea). Pliosaurids first appear in the very earliest Jurassic (Hettangian) at Dorset with Eurycleidus and other indeterminate taxa but did not (as far as is presently known) make it as far as the late Upper Cretaceous (polycotylids made it to the end). The term 'pliosaur' should not be used as it refers to an ecotype and not a clade.

Plesiosaurs represent a derived clade in the Sauropterygia Owen, 1860. This group contains a Triassic radiation of amphibious - marine forms long lumped together as a paraphyletic 'Nothosauria' but now consisting of discrete clades that became less land-dependent and more derived in style of paraxial locomotion (i.e. they grade up to the flight of plesiosaurs). Glen Storrs recognizes the most derived 'nothosaurs' (Nothosaurus, Pistosaurus and relatives) as forming the clade Nothosauriformes with the plesiosaurs. Basal- and non-nothosauriforms are predominantly Tethyan in distribution and the presence of the pachypleurosaurs - a clade of lizard-shaped amphibious, small-bodied reptiles - here too suggests that this is the sauropterygian home. Pachypleurosaurs have traditionally been regarded as 'nothosaurs' too but they are increasing regarded as a sauropterygian out-group. Whatever, they are primitive members of the group that includes plesiosaurs.

Placodonts are a problem. Rieppel and Storrs have them as true sauropterygians, but this is mildly controversial. The most comprehensive and current view of placodont relationships is a paper by Mazin in Geobios. It's in French and I haven't understood it all yet. Cladistic analysis of sauropterygian and placodont characters by Rieppel did nest Placodontia within Sauropterygia. If this view does not become accepted, perhaps resurrection of a Euryapsida (Placodontia + Sauropterygia) will do.

These reptiles are modified diapsids and may be neodiapsids up there in the younginiform-sauria crown group. I'm unaware of any derived characters that link sauropterygians (incl. placodonts) with either younginiforms or lepidosaurian saurians (cases have been made for both alternatives). On the other hand, perhaps the nearest relatives to sauropterygians are araescelidians (incl. Petrolacosaurus) in which case they are basal diapsids and not neodiapsids. The description in recent years of a (probable) marine araescelidian with swimming adaptations, Spinoequalis, implies that this relationship is a possibility.

The full text of this comment is available at the Archives of the DINOSAUR mailing list, June 9, 1997.

Skeletal drawing of the polycotylid,  Dolichorhynchops osborni

(Adapted from Buchanan, 1984, based on KUVP 1300)


For more information on Jurassic plesiosaurs: Adam Smith's The Plesiosaur Directory


Adams, D. A. 1977. Trinacromerum bonneri, a new polycotylid plesiosaur from the Pierre Shale of South Dakota and Wyoming.   Unpublished Masters thesis, University of Kansas, 97 pages.

Adams, D. A. 1997. Trinacromerum bonneri, new species, last and fastest pliosaur of the Western Interior Seaway. Texas Journal of Science, 49(3):179-198. (See O'Keefe, F. R. 2008)

Bonner, O. W. 1964. An osteological study of Nyctosaurus and Trinacromerum with a description of a new species of Nyctosaurus, Unpub. Masters Thesis, Fort Hays State University, 63 pages.

Carpenter, K. 1996. A Review of short-necked plesiosaurs from the Cretaceous of the western interior, North America, Neues Jahrbuch für Geologie und Paläeontologie Abhandlungen, (Stuttgart) 201(2):259-287.

Carpenter, K. 1997. Comparative cranial anatomy of two North American Cretaceous plesiosaurs, pp. 191-216, In Calloway, J. M. and E. L. Nicholls, (eds.), Ancient Marine Reptiles, Academic Press.

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

Cope, E. D. 1869. [Remarks on fossil reptiles, Clidastes propython, Polycotylus latipinnis, Ornithotarsus immanis.]. Proceedings of the American Philosophical Society xi p. 117. (meeting of June 18, 1869)

Cope, E. D. 1870. Remarks on fossil reptiles from the Cretaceous of Kansas. Proceedings of the Academy of Natural Sciences of Philadelphia, p. 132. (Polycotylus latipinnis)

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.

Cragin, F. W. 1888. Preliminary description of a new or little known saurian from the Benton of Kansas, American Geologist 2:404-407.

Druckenmiller, P. S. 1998. Osteology and relationships of a plesiosaur (Sauropterygia) from the Thermopolis Shale (Lower Cretaceous) of Montana. Unpublished Masters Thesis, Montana State University.

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

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. 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.  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. 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. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 320 pp. ISBN: 0253345472

Everhart, M. J. 2007. Sea Monsters: Prehistoric Creatures of the Deep. National Geographic, 192 p.    ISBN-13: 978-1426200854


Everhart, M. J. 2007. Historical note on the 1884 discovery of Brachauchenius lucasi (Plesiosauria; Pliosauridae) in Ottawa County, Kansas. Kansas Academy of Science, Transactions 110(3-4):255-258.


Everhart, M.J. 2009. Probable plesiosaur remains from the Blue Hill Shale (Carlile Formation; Middle Turonian) of north central Kansas. Kansas Academy of Science, Transactions 112(3/4):215-221.


Knight, W. C. 1898. Some new Jurassic vertebrates  from Wyoming. Amer. Jour. Sci., ser. 4, 5(29):378-380. [Megalneusaurus rex, a giant pliosaurid]

Lingham-Soliar, T. 2000. Plesiosaur locomotion: Is the four-wing problem real or merely an atheoretical exercise? Neues Jahrbuch für Geologie und Paläeontologie Abhandlungen, (Stuttgart) 217:45-87.

Lucas, F. A. 1903. A new plesiosaur. Smithsonian Miscellaneous Collections 45:96, pl. XXVIII (Quarterly Issue Vol. 1), 1457.

Lucas, S. G. 1994. Late Cretaceous pliosaurs (Eurapsida: Plesiosauroida) from the Black Mesa Basin, Arizona, U. S. A. Journal of the Arizona-Nevada Academy of Science 28(1/2):41-45.

Martin, J. E. and L. E. Kennedy. 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. and A. J. Kihm. 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.

Moodie, R. L. 1911. An embryonic plesiosaurian propodial, Trans. Kansas Acad. Sci. 23:95-101, 9 figs, 1 pl.

O'Keefe, F. R. 1999. Phylogeny and convergence in the Plesiosauria. Journ. Vert. Paleon. 19(3):67A. (abstract)

O'Keefe, F. R. 2001. A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia). Acta Zool. Fennica 213:1-63.

O'Keefe, F. R.  2001. Ecomorphology of plesiosaur flipper geometry. J. Evol. Biol. 14:987-991.

O'Keefe, F. R. 2002. The evolution of plesiosaur and pliosaur morphotypes in the Plesiosauria (Reptilia: Sauropterygia). Paleobiology 28(1):101-112.

O'Keefe, F. R. 2004. On the cranial anatomy of the polycotylid plesiosaurs, including new material of Polycotylus latipinnis Cope, from Alabama. Journal of Vertebrate Paleontology 24(2):326-340.

O'Keefe, F. R. 2008. Cranial anatomy and taxonomy of Dolichorhynchops bonneri new combination, a polycotylid plesiosaur from the Pierre Shale of Wyoming and South Dakota. Journal of Vertebrate Paleontology 28(3):664–676.

O’Keefe, F.R. and Chiappe, L.M. 2011. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science 333(6044):870-873.

Riess, J. and E. Frey. 1991. The evolution of underwater flight and the locomotion of plesiosaurs. pp. 131-144, In Rayner, J. M. V. and R. J.  Wooton (eds.), Biomechanics in evolution. Cambridge Univ. Press.

Riggs, E. S. 1944. A new polycotylid plesiosaur. University of Kansas Science Bulletin 30:77-87.

Robinson, J. A. 1975. The locomotion of plesiosaurs, N. Jb. Geol. Paläont. Abh., 149, 3:286-332.

Russell, D. A. 1967. Cretaceous vertebrates from the Anderson River N. W. T. Canadian Journal of Earth Sciences 4:21-38.

Russell, L. S. 1935. A plesiosaur from the Upper Cretaceous of Manitoba. Jour. Paleon. 9:385-389.

Sato, T. and K. Tanabe. 1998. Cretaceous plesiosaurs ate ammonites, Nature, 394:629-630.

Schmeisser, R.L. and Gillette, D.D. 2009. Unusual occurrence of gastroliths in a polycotylid plesiosaur from the Upper Cretaceous Tropic Shale, southern Utah. PALAIOS 2009 24: 453-459.

Schultze, H.-P., L. Hunt, J. Chorn and A.M. Neuner. 1985. Type and figured specimens of fossil vertebrates in the collection of the University of Kansas Museum of Natural History, Part II. Fossil Amphibians and Reptiles. Miscellaneous Publications of the University of Kansas Museum of Natural History 77:66 pp.

Schumacher, B. A. and M. J. Everhart. 2004. A new assessment of plesiosaurs from the old Fort Benton Group, Central Kansas. Joint Annual Meeting of the Kansas and Missouri Academies of Science, p. 50.

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.

Schumacher, B. A. and J. E. Martin. 1995. Polycotylus sp.: A short-necked plesiosaur from the Niobrara Formation (Upper Cretaceous) of South Dakota. Jour. Vert. Paleon. 15(suppl. to 3):52A.

Sternberg, G. F. and M. V. Walker. 1957. Report on a plesiosaur skeleton from western Kansas. Kansas Academy of Science, Transactions, 60(1):86-87.

Tarsitano, S. and J. Riess. 1982. Plesiosaur locomotion - underwater flight versus rowing. Neues Jahrbuch für Geologie und Paläeontologie Abhandlungen, (Stuttgart) 164:188-192.

Tarsitano, S. and J. Riess. 1982. Considerations concerning plesiosaur locomotion. Neues Jahrbuch für Geologie und Paläeontologie Abhandlungen, (Stuttgart) 164:193-194.

Thurmond, J. T. 1968. A new polycotylid plesiosaur from the Lake Waco Formation (Cenomanian) of Texas. Journal of Paleontology 42:1289-1296.

Williston, S. W. 1902. Restoration of Dolichorhynchops osborni, a new Cretaceous plesiosaur, Kansas University Science Bulletin, 1(9):241-244, 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, American Journal of  Science, series 4, 21(123):221-234, 4 pl.

Williston, S. W. 1907. The skull of Brachauchenius, with special observations on the relationships of the plesiosaurs. United States National Museum Proceedings 32:477-489. pls. 34-37.

Williston, S. W. 1908. North American plesiosaurs: Trinacromerum. Journal of Geology 16:715-735. figs. 1-15.

Williston, S. W. 1914. Water reptiles of the past and present. Chicago Univ. Press. 251 pp

Other Plesiosaur information on the Internet:


Barry Kazmer's Plesiosaur Paleontology: Barry is digging plesiosaur remains from a quarry in southeastern South Dakota.

Plesiosaur References: A listing of publications related to plesiosaurs from Barry Kazmer's Plesiosaur Paleontology web site.

Australian Mesozoic Marine Reptiles Dann Pigdon's page about plesiosaurs, pliosaurs and ichthyosaurs from Down Under.

Plesiosauria Translation and Pronunciation Guide - An excellent reference by Ben Creisler

Giant pliosaurs -- real and imaginary - A reality check on pliosaurids by Ben Creisler

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

Richard Forrest's listing of plesiosaur specimens and literature - The Plesiosaur Site

Richard Forrest's 5 Questions about Plesiosaurs (serious stuff!)

The Denver Museum elasmosaur (Thalassomedon haningtoni)

"The longest neck in the ocean" (University of Nebraska State Museum elasmosaurs)

A primer on the anatomy of the plesiosaur skull.

Large gastroliths from a Kansas elasmosaur.

Plesiosaur stomach contents and gastroliths

Ben Creisler's Plesiosaur Translation and Pronunciation Guide

Adam Stuart Smith's Sea Saur Page