Dolichorhynchops

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Dolichorhynchops
Fossil range: Late Cretaceous

Dolichorhynchops osborni from the Late Cretaceous of North America

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Sauropterygia
Order:	Plesiosauria
Suborder:	Plesiosauroidea
Family:	Polycotylidae
Genus:	Dolichorhynchops

Species

D. osborni
D. herschelensis

Dolichorhynchops is a genus of polycotylid plesiosaur from the Late Cretaceous of North America, containing two species, D. osborni and D. herschelensis. Simply put, Dolichorhynchops (also known as "Dolly" to paleontologists) was an oceangoing prehistoric reptile. Its Greek generic name means "long-nosed eye," perhaps with reference to the fact that its eyes seem placed rather far forward on its lengthy snout.

[edit] D. osborni

The holotype specimen of Dolichorhynchops osborni was discovered in the upper Smoky Hill Chalk Logan County, Kansas, by George F. Sternberg, as a teenager, in around 1900. The remains were collected by him and his father, Charles H. Sternberg, and then sold to the University of Kansas (Lawrence, Kansas). KUVP 1300 was prepared and mounted by H.T. Martin under the supervision of Dr. S.W. Williston, who described and named it in 1902. A more detailed description and photographs were provided by Williston 1903). The specimen has been on display in the KU Museum of Natural History since that time.

In 1918, Charles H. Sternberg found a large mosasaur with the remains of a plesiosaur in its stomach. The mosasaur specimen is currently mounted in the United States National Museum (Smithsonian) and the plesiosaur remains are stored in the collections. Although these important specimens were briefly reported by C. H. Sternberg (1922), the information was lost to science until 2001. This specimen was rediscovered and described by Everhart (2004a). It is the basis for the story line in the new (2007) National Geographic IMAX movie - Sea Monsters, and a book by the same name (Everhart, 2007).

George Sternberg found a second, less complete specimen of D.osborni in 1926. In his effort to sell the specimen to a museum, Sternberg took detailed photographs of the skull. The specimen was eventually mounted in plaster and was acquired by the Harvard Museum of Comparative Zoology. MCZ 1064 was on display there until some time in the 1950s. This specimen was never completely described although the skull was figured by O'Keefe (2004). (See also Everhart, 2004b)

The specimen of D. osborni on exhibit at the Sternberg, FHSM VP-404 was found by Marion Bonner near Russell Springs in Logan County in the early 1950s. It is, perhaps, the most complete specimen of this species known. It is just under 10 feet in length. The skull was crushed flat but is in very good condition. This specimen was initially reported by Sternberg and Walker (1957), and then was the subject of a Masters thesis by Orville Bonner (1964). Note that it was described by Bonner as "Trinacromerum osborni" which was the accepted genus name at the time.

Two very large specimens of a polycotylid plesiosaur ([http://www.oceansofkansas.com/Pliosaurs/KU40001/KU40001-4.jpg KUVP 40001 and 40002)were collected from the Pierre Shale of Wyoming and later reported on by Adams in her 1977 Masters thesis. Later (1997), she officially described (1997) as a new species of Trinacromerum (T. bonneri). Unknown to her at the time, Carpenter (1996) had revised the Polycotylidae and separated Dolichorhynchops from Trinacromerum. Thus the species would revert back to Dolichorhynchops bonneri, but there is some question as to whether or not the specimens represent a separate species or just larger individuals of D. osborni. The question has yet to be resolved.

Until recently, all known specimens of D. osborni in Kansas had been collected from the upper layers of the Smoky Hill Chalk (Campanian age). Everhart (2003) reported the first remains from the lower chalk (Late Coniacian-Santonian in age). In 2005, the remains of the earliest known D. osborni were discovered in the Fort Hays Limestone in Jewell County, Kansas. This is the first record of a polycotylid plesiosaur in this formation (Everhart, Decker and Decker, 2006).

[edit] D. herschelensis

D. herschelensis was described as a new species in 2005. It was discovered in the Bearpaw Formation of Saskatchewan, Canada, a Late Cretaceous (late Campanian to Maastrichtian) rock formation. The fossil was found close to the town of Herschel in south-western Saskatchewan, from which the species name is derived. The rock formation it was found in consists of sandstones, mudstones and shales laid down in the Western Interior Seaway, just before it began to revert to dry land.

The type specimen of D. herschelensis was discovered in a disarticulated state (ie the bones were scattered about the discovery site). The skull, lower jaw, ribs, pelvis and shoulder blades were all recovered, but the spine was incomplete, so the exact number of vertebrae the living animal would have had is unknown. All four limbs are missing, with the exception of 9 small Phalanges (finger bones) and a small number of limb bones found close by which may belong to the animal in question. The specimen is believed to be an adult, due to the fusion of certain bones (it is generally assumed—not necessarily strictly correctly so—that other animals' skulls, much as humans', consist of dissociated bones interconnected by cartilage fontanelles that do not entirely close until full maturity). It is also believed to have been substantially smaller than its close relative, D. osborni, as some juvenile specimens of D. osborni are larger than the adult specimen of D. herschelensis. Assuming that only a few vertebrae are missing from the skeleton, the animal is estimated to be about 2.5 to 3 metres in length. The snout is long and thin, with numerous tooth sockets. However, very few of the thin, sharp teeth remain.

[edit] References

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.

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.

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. 2004a. 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. 2004b. 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. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 322 pp.

Everhart, M.J., R. Decker and P. Decker. 2006. Earliest remains of Dolichorhynchops osborni (Plesiosauria: Polycotylidae) from the basal Fort Hays Limestone, Jewell County, Kansas. Kansas Academy of Science, Transactions 109(3-4): 261 (abstract).

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

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.

Sato, T., 2005. A new Polycotylid Plesiosaur (Reptilia: Sauropterygia) from the Upper Cretaceous Bearpaw Formation in Saskatchewan, Canada. Journal of Paleontology, 79: 969-980.

Sternberg, C. H. 1922. Explorations of the Permian of Texas and the chalk of Kansas, 1918. Kansas Academy of Science, Transactions 30(1): 119-120.

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.

Williston, S. W. 1902. Restoration of Dolichorhynchops osborni, a new Cretaceous plesiosaur, Kansas University Science Bulletin, 1(9):241-244, 1 plate.