''Styxosaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

plesiosaur The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared ...

of the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Elasmosauridae. ''Styxosaurus'' lived during the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

. Two species are known: ''S. snowii'' and ''S. browni''.

Description

''Styxosaurus'' was a large plesiosaur, one of several species of a group collectively called elasmosaurs that appeared in the Late Cretaceous. Elasmosaurs typically have a neck that is at least half the length of the body, and composed of 60-72 vertebrae. ''Styxosaurus'' was a large elasmosaur with a long neck. It reached in length and in body mass. Its sharp

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

were conical and were adapted to puncture and hold rather than to cut; like other

plesiosaurs The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared i ...

, ''Styxosaurus''

swallowed Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. Swallowing ...

its food whole.

Discovery

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen of ''Styxosaurus snowii'' was described by S.W. Williston from a complete skull and 20 vertebrae. Another more complete specimen - SDSMT 451 was discovered near Iona, South Dakota, also in the US, in 1945. The specimen was originally described and named ''Alzadasaurus pembertoni'' by Welles and Bump (1949) and remained so until it was synonymized with ''S. snowii'' by Carpenter. Its chest cavity contained about 250

gastroliths A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In oth ...

, or "stomach stones". Although it is mounted at the School of Mines as if its head were looking up and out of the water, such a position would be physically impossible. ''Styxosaurus'' is named for the mythological

River Styx In Greek mythology, Styx (; grc, Στύξ ) is a river that forms the boundary between Earth (Gaia) and the Underworld. The rivers Acheron, Cocytus, Lethe, Phlegethon, and Styx all converge at the centre of the underworld on a great marsh, whi ...

('), which separated the

Greek underworld In mythology, the Greek underworld, or Hades, is a distinct realm (one of the three realms that makes up the cosmos) where an individual goes after death. The earliest idea of afterlife in Greek myth is that, at the moment of death, an individ ...

from the world of the living. The ''-saurus'' part comes from the Greek ' (), meaning "lizard" or "reptile." The type specimen was found on Hell Creek in

Logan County, Kansas Logan County (standard abbreviation: LG) is a county located in the U.S. state of Kansas. As of the 2020 census, the county population was 2,762. The largest city and county seat is Oakley. The county was named for Gen. John A. Logan. One ...

and is the source of the genus name coined by

Samuel Paul Welles Samuel Paul Welles (November 9, 1907 – August 6, 1997) was an American palaeontologist. Welles was a research associate at the Museum of Palaeontology, University of California, Berkeley. He took part in excavations at the Placerias Quarry in ...

, who described the genus, in 1943.

Classification

''Styxosaurus snowii'' is from a group called elasmosaurs, and is closely related to ''

Elasmosaurus platyurus ''Elasmosaurus'' (;) is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, about 80.5million years ago. The first specimen was discovered in 1867 near Fort Wallace, Kansas, US, and was sent ...

'', which was found in

Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...

, USA, in 1867. The first ''Styxosaurus'' to be described was initially called ''Cimoliasaurus snowii'' by S.W. Williston in 1890. The specimen included a complete

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

and more than 20

cervical vertebrae In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

KUVP 1301
that were found near Hell Creek in western Kansas by Judge E.P. West. The name was later changed to ''Elasmosaurus snowii'' by Williston in 1906 and then to ''Styxosaurus snowii'' by Welles in 1943.Welles, S. P. 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. University of California Memoirs 13:125-254. figs.1-37., pls.12-29. A second species, ''Styxosaurus browni'', was named by Welles in 1952. Although synonymized with '' Hydralmosaurus serpentinus'' in 1999, it has been recently revalidated.Carpenter, K. 1999. Revision of North American elasmosaurs from the Cretaceous of the western interior. Paludicola 2(2):148-173. The following

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

shows the placement of ''Styxosaurus'' within Elasmosauridae following an analysis by Rodrigo A. Otero, 2016:

Palaeobiology

While most

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

s do not use gastroliths for grinding of food, almost all reasonably complete elasmosaur specimens include gastroliths. Although it is possible ''Styxosaurus'' may have used the stones as

ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship, ...

, a ''Styxosaurus'' specimen found in the Pierre Shale of western Kansas included ground up fish bones mixed with the gastroliths. In addition, the weight of the gastroliths found in elasmosaur specimens is always much less than 1% of the estimated weight of the living animal. While

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...

s and some other animals may use gastroliths for ballast today, it appears likely that elasmosaurs used them as a gastric mill. See Henderson (2006) contra Wings (2004).Wings, Oliver (2004): Identification, distribution, and function of gastroliths in dinosaurs and extant birds with emphasis on ostriches (''Struthio camelus''). Ph.D. Thesis, The University of Bonn, Bonn, Germany, 187 pp. URN: urn:nbn:de:hbz:5N-0462
PDF fulltext
''Styxosaurus'', like most other plesiosaurs, probably fed on belemnites, fish (''

Gillicus ''Gillicus'' was a relatively small, 2-metre long ichthyodectiform fish that lived in the Western Interior Seaway, in what is now central North America, during the Late Cretaceous. Description Like its larger relative, ''Ichthyodectes ctenodon ...

'', etc.) and squid. With its interlocking teeth, ''Styxosaurus'' could grab on to its slippery

prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

before swallowing it.

Gallery

References

Sources

*Everhart, M. J. 2000. Gastroliths associated with plesiosaur remains in the Sharon Springs Member of the Pierre Shale (Late Cretaceous), western Kansas. ''Transactions of the Kansas Academy of Science'' 103(1-2): 58–69. *Cicimurri, D. J. and M. J. Everhart, 2001. An elasmosaur with stomach contents and gastroliths from the Pierre Shale (late Cretaceous) of Kansas. ''Kansas Acad. Sci. Trans'' 104(3-4):129-143. *Everhart, M. J. 2005a. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 320 pp. *Everhart, M. J. 2005b. 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. *Everhart, M. J. 2006. The occurrence of elasmosaurids (Reptilia: Plesiosauria) in the Niobrara Chalk of Western Kansas. ''Paludicola'' 5(4):170-183. *Henderson, J. 2006. Floating point: a computational study of buoyancy, equilibrium, and gastroliths in plesiosaurs. ''Lethaia'' 39: 227–244. *Welles, S. P. 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. ''University of California Memoirs'' 13:125-254. figs.1-37., pls.12-29. *Welles, S. P. 1952. A review of the North American Cretaceous elasmosaurs. ''University of California Publications in Geological Sciences'' 29:46-144. figs. 1-25. *Welles, S. P. 1962. A new species of elasmosaur from the Aptian of Columbia and a review of the Cretaceous plesiosaurs. University of California Press, Berkeley and Los Angeles. *Welles, S. P. and Bump, J. 1949. ''Alzadasaurus pembertoni'', a new elasmosaur from the Upper Cretaceous of South Dakota. ''Journal of Paleontology'' 23(5): 521–535. * * * *

External links

''Styxosaurus''
at Oceans of Kansas

at National Geographic
Styxosaurus snowii
at Sachs Vertebrate Palaeontology Research {{Taxonbar, from=Q2555300 Late Cretaceous plesiosaurs of North America Elasmosaurids Fossil taxa described in 1943 Taxa named by Samuel Paul Welles Sauropterygian genera