''Styxosaurus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

plesiosaur The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Elasmosauridae Elasmosauridae, often called elasmosaurs or elasmosaurids, is an extinct family of plesiosaurs that lived from the Hauterivian stage of the Early Cretaceous to the Maastrichtian stage of the Late Cretaceous period (c. 130 to 66 mya). The taxo ...

. ''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. Campa ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something 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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period. Three species are known: ''S. snowii'', ''S. browni'', and ''S. rezaci''.

Discovery

The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen of ''Styxosaurus snowii'' a complete skull and 20 vertebrae and was first described by S.W. Williston ''Styxosaurus'' is named for the mythological

River Styx In Greek mythology, Styx (; ; lit. "Shuddering"), also called the River Styx, is a goddess and one of the rivers of the Greek Underworld. Her parents were the Titans Oceanus and Tethys, and she was the wife of the Titan Pallas and the mothe ...

('), which separated the

Greek underworld In Greek mythology, the underworld or Hades () is a distinct realm (one of the three realms that make 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 individu ...

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 is a county located in the U.S. state of Kansas. Its county seat and largest city is Oakley. As of the 2020 census, the county population was 2,762. The county was named for John Logan, a general during the American Civil ...

, which is the source of the genus name coined by Samuel Paul Welles, who described the genus in 1943. 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, 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. In 2023, Elliott Smith and Robin O'Keefe also assigned this specimen to ''Styxosaurus'' but considered it to be indeterminate at the species level. In 2023, another species of ''Styxosaurus'', ''S. rezaci'', was named by Smith and O'Keefe, based on a specimen from the

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...

previously thought to belong to '' Thalassomedon''.

Description

''Styxosaurus'' was a large elasmosaur, with a long neck measuring about in total. The ''S. snowii'' specimen NJSM 15435 was reported to measure , though it lacks the skull and the frontmost neck vertebrae. The cranium of the holotype measures long, with its mandible measuring long. 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 In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the ''apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines, ...

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

plesiosaurs The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

, ''Styxosaurus''

swallowed Swallowing, also called deglutition or inglutition in scientific and medical contexts, is a physical process of an animal's digestive tract (e.g. that of a human body) that allows for an ingested substance (typically food) to pass from the mou ...

its food whole.

Classification

''Styxosaurus snowii'' is from a group called elasmosaurs, and is closely related to '' Elasmosaurus platyurus'', which was found in

Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...

, 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, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

and more than 20

cervical vertebrae In tetrapods, cervical vertebrae (: 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 saurop ...

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'' by Kenneth Carpenter in 1999, it was revalidated by Rodrigo A. Otero in 2016.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 language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

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

Palaeobiology

While most

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

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 dense material used as a weight 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 ''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 more loosely to include ...

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

prey Predation is a biological interaction in which 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 ki ...

before swallowing it.

Gallery

Notes

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 Elasmosauridae Fossil taxa described in 1943 Taxa named by Samuel Paul Welles Sauropterygian genera