Styxosaurus

{{Short description|Extinct genus of reptiles}} {{Automatic taxobox | fossil_range = Late Cretaceous, 100.5-72.1 Ma, {{Fossil range|Cenomanian|Campanian}} <ref>{{cite web |title=International Stratigraphic Chart v2021/05 |url=https://web.archive.org/web/20210605053042/https://stratigraphy.org/ICSchart/ChronostratChart2021-05.jpg}}</ref> | image = Styxosaurus snowii skull.jpg | image_upright = 1.15 | image_caption = Holotype skull of ''Styxosaurus snowii'' | taxon = Styxosaurus | authority = Welles, 1943 | subdivision_ranks = Species | subdivision = * {{extinct}}'''''S. snowii''''' (Williston, 1890; type) * {{extinct}}'''''S. browni''''' Welles, 1952 * {{extinct}}'''''S. rezaci''''' Smith & O'Keefe, 2023 | synonyms = *''Cimoliasaurus snowii'' Williston, 1890 *''Elasmosaurus snowii'' (Williston, 1890) *''Ogmodirus ischiadicus'' Williston & Moodie, 1903/1913 *''Thalassonomosaurus marshi'' (Williston, 1906) Welles, 1943 [originally ''Elasmosaurus''] *''Alzadasaurus pembertonii'' Welles & Bump, 1949 *''Alzadasaurus kansasensis'' Welles, 1952 }}

'''''Styxosaurus''''' is a genus of elasmosaurid plesiosaur that lived during the Late Cretaceous period. Three species are known: '''''S. snowii''''', '''''S. browni''''', and '''''S. rezaci'''''. Fossils are known from North America and are mainly found in the Niobrara and Pierre Shale formations. Older fossils are known from the Graneros Shale.<ref name="SO23" />

==Discovery== {{multiple image | align = left | direction = vertical | total_width = 200 | image1 = Styxosaurus snowii skull diagram.jpg | image2 = Styxosaurus browni skull diagram.jpg | footer = Skull diagrams of ''S. snowii'' (top) and ''S. browni'' (bottom) }} The holotype specimen of ''Styxosaurus snowii'' a complete skull and 20 vertebrae and was first described by S.W. Williston<ref name=Williston_1890_Structure/><ref name=Williston_1890_New/> ''Styxosaurus'' is named for the mythological River Styx (''{{lang|grc|Στυξ}}''), which separated the Greek underworld from the world of the living. The ''-saurus'' part comes from the Greek ''{{lang|grc-Latn|sauros}}'' ({{lang|grc|σαυρος}}), meaning "lizard" or "reptile." The type specimen was found on Hell Creek in Logan County, Kansas, which is the source of the genus name coined by Samuel Paul Welles, who described the genus in 1943.<ref name="Welles, S. P 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.<ref name=carpenter1999/> 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.<ref>{{cite book|last=Everhart|first= M. J.|year=2005|title=Oceans of Kansas - A Natural History of the Western Interior Sea|publisher=Indiana University Press}}</ref> In 2023, Elliott Smith and Robin O'Keefe also assigned this specimen to ''Styxosaurus'' but considered it to be indeterminate at the species level.<ref name="SO23" />

In 2023, another species of ''Styxosaurus'', ''S. rezaci'', was named by Smith and O'Keefe, based on a specimen from the Cenomanian of Nebraska previously thought to belong to ''Thalassomedon''.<ref name="SO23">{{cite journal|last1=Smith|first1=E.A.|last2=O'Keefe|first2=F.R.|year=2023|title=Occurrence of ''Styxosaurus'' (Sauropterygia: Plesiosauria) in the Cenomanian: Implications for relationships of elasmosaurids of the Western Interior Seaway|journal=Journal of Systematic Palaeontology|volume=21|issue=1|article-number=2242846|doi=10.1080/14772019.2023.2242846|bibcode=2023JSPal..2142846A }}</ref>

==Description== ''Styxosaurus'' was a large elasmosaur, with a long neck measuring about {{convert|5.25|m|ft}} in total.<ref name=carpenter1999/><ref name="gorman2016">{{cite journal | first1 = J.P. | last1 = O'Gorman | title = A Small Body Sized Non-Aristonectine Elasmosaurid (Sauropterygia, Plesiosauria) from the Late Cretaceous of Patagonia with Comments on the Relationships of the Patagonian and Antarctic Elasmosaurids | journal = Ameghiniana | volume = 53 | issue = 3 | pages = 245–268 | doi = 10.5710/AMGH.29.11.2015.2928 | year = 2016| s2cid = 133139689 | url = http://sedici.unlp.edu.ar/handle/10915/108247 | hdl = 11336/54311 | hdl-access = free }}</ref> The ''S. snowii'' specimen NJSM 15435 was reported to measure {{cvt|10|m|ft}}, though it lacks the skull and the frontmost neck vertebrae.<ref>{{Cite journal|author=Mike Everhart|title=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''|volume=2|issue=2|url=http://www.palarch.nl/wp-content/everhart_mj_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_palarchs.pdf|year=2005|journal=PalArch's Journal of Vertebrate Paleontology|access-date=2009-10-02|archive-url=https://web.archive.org/web/20110716064113/http://www.palarch.nl/wp-content/everhart_mj_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_palarchs.pdf|archive-date=2011-07-16|url-status=live}}</ref> The size of specimen SDSM 451 assigned to ''Styxosaurus'' sp. is estimated around {{convert|11.3|m|ft}} in body length and {{convert|3.1|MT|ST}} in body mass.<ref>{{cite journal|last=Zhao |first=R. J. |year=2026 |title=Body reconstruction and size estimation of plesiosaurs |journal=PeerJ |volume=14 |article-number=e21146 |doi=10.7717/peerj.21146 |doi-access=free }}</ref> The cranium of the holotype measures {{cvt|42|cm|ft}} long, with its mandible measuring {{cvt|48|cm|ft}} long.<ref name=carpenter1999/> Its sharp teeth were conical and were adapted to puncture and hold rather than to cut; like other plesiosaurs, ''Styxosaurus'' swallowed its food whole.<ref name=natgeo>{{cite web |url=http://animals.nationalgeographic.com/animals/prehistoric/styxosaurus.html |archive-url=https://web.archive.org/web/20071015060155/http://animals.nationalgeographic.com/animals/prehistoric/styxosaurus.html |archive-date=October 15, 2007 |title= National Geiographic "Styxosaurus" |access-date=2008-02-21}}</ref>

==Classification== thumb|left|Skull of ''S. browni'' ''Styxosaurus snowii'' is from a group called elasmosaurs, and is closely related to ''Elasmosaurus platyurus'', which was found in Kansas, USA, in 1867.<ref>{{cite web |url=http://www.oceansofkansas.com/SDSMT2.html |title= oceansofkansas.com|access-date=2008-02-21}}</ref>

The first ''Styxosaurus'' to be described was initially called ''Cimoliasaurus snowii'' by S.W. Williston in 1890.<ref name=Williston_1890_Structure/> The specimen included a complete skull and more than 20 cervical vertebrae ( [http://www.oceansofkansas.com/KS-Plesio.html KUVP 1301]) that were found near Hell Creek in western Kansas by Judge E.P. West.<ref name=Williston_1890_Structure/>

The name was later changed to ''Elasmosaurus snowii'' by Williston in 1906<ref name=Williston_1906/> and then to ''Styxosaurus snowii'' by Welles in 1943.<ref name="Welles, S. P 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.</ref>

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.<ref name=carpenter1999>Carpenter, K. 1999. Revision of North American elasmosaurs from the Cretaceous of the western interior. Paludicola 2(2):148-173.</ref><ref>Otero RA. (2016) Taxonomic reassessment of Hydralmosaurus as Styxosaurus: new insights on the elasmosaurid neck evolution throughout the Cretaceous. PeerJ 4:e1777 https://doi.org/10.7717/peerj.1777</ref>

The following cladogram shows the placement of ''Styxosaurus'' within Elasmosauridae following an analysis by Otero, 2016:<ref>{{cite journal|last1=Otero|first1=R. A.|title=Taxonomic reassessment of ''Hydralmosaurus'' as ''Styxosaurus'': new insights on the elasmosaurid neck evolution throughout the Cretaceous|journal=PeerJ|date=2016|volume=4|article-number=e1777|doi=10.7717/peerj.1777|pmid=27019781|pmc=4806632 |doi-access=free }}</ref> {{clade| style=font-size:85%; line-height:85%; |label1=Elasmosauridae |1={{clade |1=''Eromangasaurus carinognathus'' |2={{clade |1=''Callawayasaurus colombiensis'' |2={{clade |1=''Libonectes morgani'' |2={{clade |1={{clade |1=''Tuarangisaurus keyesi'' |2=''Thalassomedon haningtoni'' }} |2={{clade |1=CM Zfr 115 |2={{clade |1=''Hydrotherosaurus alexandrae'' |2=''Futabasaurus suzukii'' }} }} |3={{clade |label1=Aristonectinae |1={{clade |1=''Kaiwhekea katiki'' |2={{clade |1=''Alexandronectes zealandiensis'' |2={{clade |1=''Morturneria seymourensis'' |2={{clade |1=''Aristonectes parvidens'' |2=''Aristonectes quiriquinensis'' }} }} }} }} |label2=Elasmosaurinae |2={{clade |1=''Terminonatator pointeixensis'' |2={{clade |1={{clade |1=''Elasmosaurus platyurus'' |2=''Albertonectes vanderveldei'' }} |2={{clade |1='''''Styxosaurus''''' sp. (="''Hydralmosaurus serpentinus''") |2={{clade |1='''''Styxosaurus snowii''''' |2='''''Styxosaurus browni''''' }} }} }} }} }} }} }} }} }} }}

==Palaeobiology== While most predators 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, a ''Styxosaurus'' specimen found in the Pierre Shale of western Kansas included ground up fish bones mixed with the gastroliths.<ref>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. </ref> 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.<ref>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. </ref>

While crocodiles 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).<ref>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-04626 [http://hss.ulb.uni-bonn.de/diss_online/math_nat_fak/2004/wings_oliver/ PDF fulltext] {{Webarchive|url=https://archive.today/20070716032356/http://hss.ulb.uni-bonn.de/diss_online/math_nat_fak/2004/wings_oliver/ |date=2007-07-16 }}</ref>

''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 before swallowing it.

== Gallery == {{gallery |File:Styxosaurus and Xiphactinus.jpg|Restoration of ''Styxosaurus'' and ''Xiphactinus'' |File:Styxosaurus_snowii.png|Restoration |File: Canadian Fossil Discovery Centre Morden Manitoba Canada.JPG|Fossil skull and neck}}

==See also== {{Portal|Paleontology}} * List of plesiosaur genera * Timeline of plesiosaur research

==Notes== {{Notelist}}

==References== {{Reflist|2|refs= <ref name=Williston_1890_New>{{cite journal |author=Williston S. W. |title=A New Plesiosaur from the Niobrara Cretaceous of Kansas |journal=Transactions of the Annual Meetings of the Kansas Academy of Science |year=1890b |volume=12 |pages=174–178 |url=https://archive.org/stream/jstor-3623798/3623798#page/n1/mode/2up |doi=10.2307/3623798 |jstor=3623798 }}</ref> <ref name=Williston_1890_Structure>{{cite journal |author=Williston S. W. |title=Structure of the Plesiosaurian Skull |journal=Science |year=1890a |volume=16 |issue=405 |page=262 |jstor=1766513 |doi=10.1126/science.ns-16.405.262 |pmid=17829759 |url=https://zenodo.org/record/1448321 }} ([http://www.oceansofkansas.com/Williston90.htm text on www.oceansofkansas.com])</ref> <ref name=Williston_1906>{{cite journal |author=Williston S. W. |title=North American plesiosaurs: ''Elasmosaurus'', ''Cimoliasaurus'', and ''Polycotylus'' |journal=American Journal of Science |series=Series 4 |year=1906 |volume=21 |issue=123 |pages=221–236 |doi=10.2475/ajs.s4-21.123.221 |bibcode=1906AmJS...21..221W |url=https://zenodo.org/record/1450146 }}</ref> }}

==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. * {{cite journal |author=Williston S. W. |title=Structure of the Plesiosaurian Skull |journal=Science |year=1890a |volume=16 |issue=405 |page=262 |jstor=1766513 |doi=10.1126/science.ns-16.405.262 |pmid=17829759 |url=https://zenodo.org/record/1448321 }} * {{cite journal |author=Williston S. W. |title=A New Plesiosaur from the Niobrara Cretaceous of Kansas |journal=Transactions of the Annual Meetings of the Kansas Academy of Science |year=1890b |volume=12 |pages=174–178 |url=https://archive.org/stream/jstor-3623798/3623798#page/n1/mode/2up |doi=10.2307/3623798 |jstor=3623798 }} * {{cite journal |author=Williston S. W. |title=An Interesting Food Habit of the Plesiosaurs |journal=Transactions of the Annual Meetings of the Kansas Academy of Science |year=1891 |volume=13 |pages=121–122 |url=https://archive.org/stream/jstor-3623988/3623988#page/n1/mode/2up |doi=10.2307/3623988 |jstor=3623988 }} * {{cite journal |author=Williston S. W. |title=North American plesiosaurs: ''Elasmosaurus'', ''Cimoliasaurus'', and ''Polycotylus'' |journal=American Journal of Science |series=Series 4 |year=1906 |volume=21 |issue=123 |pages=221–236 |doi=10.2475/ajs.s4-21.123.221 |bibcode=1906AmJS...21..221W |url=https://zenodo.org/record/1450146 }}

== External links == * [http://www.oceansofkansas.com/SDSMT2.html ''Styxosaurus''] at Oceans of Kansas * [https://web.archive.org/web/20071015060155/http://animals.nationalgeographic.com/animals/prehistoric/styxosaurus.html ''Styxosaurus''] at National Geographic * [https://www.sachspal.de/styxosaurus/ Styxosaurus snowii] at Sachs Vertebrate Palaeontology Research

Category:Late Cretaceous plesiosaurs of North America Category:Elasmosauridae Category:Fossil taxa described in 1943 Category:Taxa named by Samuel Paul Welles Category:Sauropterygian genera