Xiphactinus

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Extinct genus of ray-finned fishes

title: "Xiphactinus" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["ichthyodectiformes", "marine-fish-genera", "prehistoric-ray-finned-fish-genera", "late-cretaceous-fish-of-north-america", "cretaceous-canada", "fossils-of-canada", "cretaceous-united-states", "fossils-of-the-united-states", "cretaceous-fish-of-europe", "cretaceous-fish-of-australia", "late-cretaceous-fish-of-south-america", "cretaceous-venezuela", "fossils-of-venezuela", "albian-genus-first-appearances", "cenomanian-genera", "turonian-genera", "coniacian-genera", "santonian-genera", "campanian-genera", "maastrichtian-genus-extinctions", "demopolis-chalk", "mooreville-chalk", "fossil-taxa-described-in-1870", "taxa-named-by-joseph-leidy", "cretaceous-argentina", "golfo-san-jorge-basin", "salamanca-formation"] description: "Extinct genus of ray-finned fishes" topic_path: "geography/canada" source: "https://en.wikipedia.org/wiki/Xiphactinus" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Extinct genus of ray-finned fishes ::

| image = Xiphactinus AMNH.jpg | image_caption = Mounted skeleton of X. audax at the American Museum of Natural History | fossil_range = Albian–Maastrichtian

X. vetus Leidy, 1856 | subdivision_ref = | synonyms = {{collapsible list|title=List of synonyms|
Megalodon sauroides Agassiz, 1835
Megalodon? lewesiensis Mantell, 1836
Hypsodon Agassiz, 1837
Hypsodon lewesiensis Agassiz, 1843
Saurocephalus audax Cope, 1870
Saurocephalus thaumas Cope, 1870
Portheus molossus Cope, 1871
Portheus thaumas Cope, 1871
Portheus lestrio Cope, 1873
Portheus mudgei Cope, 1874
Portheus mantelli Newton, 1877
Portheus daviesi Newton, 1877
Xiphactinus gaultinus Newton, 1877
Xiphactinus mantelli Newton, 1877
Portheus lowii Stewart, 1898
Xiphactinus molossus Stewart, 1898
Xiphactinus thaumas Stewart, 1898
Xiphactinus brachygnathus Stewart, 1899
Xiphactinus lowii Stewart, 1900
Hypsodon(?) granulosus Cockerell, 1919
Hypsodon(?) radiatulus Cockerell, 1919
Polygonodon vetus Leidy, 1856
Polygonodon rectus Emmons, 1858
Mossasaurus rectus Emmons, 1858
Portheus angulatus Cope, 1872
Xiphactinus angulatus Schwimmer et al., 1992

Xiphactinus (from Latin and Greek for "sword-ray") is an extinct genus of large predatory marine ray-finned fish that lived during the late Albian to the late Maastrichtian. It is a member of the extinct order Ichthyodectiformes, which represent close relatives of modern teleosts.

The species Portheus molossus described by Cope is a junior synonym of X. audax. Skeletal remains of Xiphactinus have come from the Carlile Shale and Greenhorn Limestone of Kansas (where the first Xiphactinus fossil was discovered during the 1850s in the Niobrara Chalk), and Cretaceous formations all over the East Coast (most notably Georgia, Alabama, North Carolina, and New Jersey) in the United States, as well as Europe, Australia, the Kanguk and Ashville Formations of Canada, La Luna Formation of Venezuela and the Salamanca Formation in Argentina.

Paleobiology

::figure[src="https://upload.wikimedia.org/wikipedia/commons/4/4c/Xiphactinus_audax.png" caption="Restoration of ''X. audax''"] ::

| image1 = Xiphactinus fossil SI.jpg | image2 = Xiphactinus sp. with Gillicus sp. in its stomach (fossil fishes) (Niobrara Formation, Upper Cretaceous; Gove County, Kansas, USA) 2 (32938717214).jpg | image3 = Xiphactinus in Denver Museum.jpg | footer = Several Xiphactinus skeletons are preserved with the fish Gillicus arcuatus swallowed whole.

Species of Xiphactinus were voracious predatory fish. At least a dozen specimens of X. audax have been collected with the remains of large, undigested or partially digested prey in their stomachs. In particular, one 4.2 m fossil "Fish-Within-A-Fish" specimen was collected by George F. Sternberg with another, nearly perfectly preserved 1.9 m long ichthyodectid Gillicus arcuatus inside of it. The larger fish apparently died soon after eating its prey, most likely owing to the smaller prey's struggling and rupturing an organ as it was being swallowed. This fossil is on display at the Sternberg Museum of Natural History in Hays, Kansas.

Like many other species in the Late Cretaceous oceans, a dead or injured individual was likely to be scavenged by sharks (Cretoxyrhina and Squalicorax). The remains of a Xiphactinus were found within a large specimen of Cretoxyrhina collected by Charles H. Sternberg. The specimen is on display at the University of Kansas Museum of Natural History. ::figure[src="https://upload.wikimedia.org/wikipedia/commons/1/1b/Xiphactinus_-_head_detail.jpg" caption="Detailed view of the skull of ''Xiphactinus'' at the [[American Museum of Natural History"] ::

Like modern tarpons, Xiphactinus likely spent its juvenile stage of life in shallow seaway margins for protection and to utilize rich food resources, possibly rare in open marine water, though this needs confirmation due to the lack of shallow, nearshore deposits from the Western Interior Seaway. The teeth of the juvenile specimen indicate that the diet of Xiphactinus probably didn't change notably during its growth, implying that even the small specimens would have been fish-eating predators.

"Unicerosaurus"

In 1982, a former Baptist minister, Carl Baugh, began excavations on the limestone beds of the Paluxy River, near Glen Rose, Texas, famous for its dinosaur tracks. Some of the tracks resembled human footprints and had been proclaimed since 1900 as evidence that dinosaurs and modern humans had once lived alongside one another. Scientists' investigations found the supposed human footprints to be "forms of elongate dinosaur tracks, while others were selectively highlighted erosional markings, and still others (on loose blocks) probable carvings." While excavating, he found a solitary "Y-shaped" fossil that he informally called "Unicerosaurus". In a 1987 popular article, John Armstrong described the fossil as a "Y-shaped petrified bone that appears to be the neural spine from a huge fish like the Portheus of Niobrara Chalk" that Baugh's museum "declared to be the forehead horn of a newly discovered dinosaur genus". The museum's exhibit told visitors that the "horn" belonged to "the unicorn of Job 38, one of three dinosaurs mentioned in Scripture; the others being behemoth and leviathan of Job 40 and 41", and that the horn was able to fold back like the blade of a jack knife. Although some Young Earth Creationists shared Baugh's interpretations of the biblical Behemoth and Leviathan, Baugh's claims were not taken seriously either by Christian organizations or the scientific community.

In popular culture

::figure[src="https://upload.wikimedia.org/wikipedia/commons/c/ce/Ichthyodectidae1.jpg" caption="ichthyodectids"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/b6/Xiphactinus_audax.jpg" caption="Depiction of a ''Xiphactinus'' swallowing a ''[[Gillicus]]''"] ::

In October 2010, Kansas House Rep. Tom Sloan (R-Lawrence) announced that he would introduce legislation to make Xiphactinus audax, a.k.a. the "X-fish", the state fossil of Kansas. Ultimately, Tylosaurus was selected instead.

Notes

References

Cope, E. D. 1871. On the fossil reptiles and fishes of the Cretaceous rocks of Kansas. Art. 6, pp. 385–424 (no figs.) of Pt. 4, Special Reports, 4th Ann. Rpt., U.S. Geol. Surv. Terr. (Hayden), 511 p. (Cope describes and names Portheus molossus)
Cope, E. D. 1872a. On Kansas vertebrate fossils. American Journal of Science, Series 3, 3(13):65.
Cope, E. D. 1872b. On the geology and paleontology of the Cretaceous strata of Kansas. Preliminary Report of the United States Geological Survey of Montana and Portions of the Adjacent Territories, Part III – Paleontology, pp. 318–349.
Cope, E. D. 1872c. [Sketch of an expedition in the valley of the Smoky Hill River in Kansas]. Proc. Amer. Phil. Soc. 12(87):174-176.
Everhart, Michael J. 2005. Oceans of Kansas – A Natural History of the Western Interior Sea. Indiana University Press, 320 pp.
Hay, O. P. 1898. Observations on the genus of Cretaceous fishes called by Professor Cope Portheus. Science, 7(175):646. Hay noted, "Professor O. P. Hay made some 'Observations on the genus of Cretaceous Fishes, called by Professor Cope Portheus " discussing the osteology of the genus at some length and particularly the skull, shoulder girdle and vertebral column. He said that in many respects it resembled the Tarpon of our Southern coasts, although possessing widely different teeth, and undoubtedly belonged to the Isospondyli. The conclusion reached that Cope's Portheus is identical with the earlier described genus Xiphactinus of Leidy. (Since the paper was read, the author has learned that Professor Williston has reached the same conclusion.)"
Leidy, J. 1856. Notices on remains of extinct vertebrated animals of New Jersey, collected by Prof. Cook of the State Geological Survey under the Direction of Dr. W. Kitchell. Proceedings of the Academy of Natural Sciences of Philadelphia, 8:221. (printed in 1857 – Naming of Polygonodon vetus, a sister species of Xiphactinus audax, and Ischyrhiza mira Leidy)
Leidy, J. 1870. [Remarks on ichthyodorulites and on certain fossil Mammalia.]. Proceedings of the Academy of Natural Sciences of Philadelphia. 22:12-13. (The naming of Xiphactinus audax from a fragment of a pectoral fin found by Dr. George M. Sternberg (then an Army Surgeon serving in Kansas) in the chalk of western Kansas --- this paper pre-dates Cope's 1872 description of Portheus molossus by over a year).
Shimada, K. and M. J. Everhart. 2004. Shark-bitten Xiphactinus audax (Teleostei: Ichthyodectiformes) from the Niobrara Chalk (Upper Cretaceous) of Kansas. The Mosasaur 7, p. 35-39.
Stewart, A. 1898. Individual variations in the genus Xiphactinus Leidy. Kansas Univ. Quar. 7(3):116-119, pl. VII, VIII, IX, X. Stewart placed a short note on page 116 acknowledging that Xiphactinus Leidy 1870 has priority over Portheus Cope 1872. "Xiphactinus audax Leidy (Proc. Acad. Sci. Phila., 1870, p. 12) has been shown to the a synonym of Saurocephalus Cope (U.S. Geol. Surv., Wyoming, etc. 1872, p. 418). In a letter to Prof. Mudge, dated October 28, 1870, which will shortly be published in the fourth volume of the Kansas University Geological Survey, Cope refers it to Saurocephalus thaumas (Portheus thaumas Cope). After carefully comparing the description and figure of the pectoral spine of X. audax I was led to the same conclusion; and as the genus Portheus was not made known by Cope until 1871 (Proc. Am. Phil. Soc., 1871, p. 173), according to the rules of nonclamature Xiphactinus should have priority."
Stovall, J. W. 1932. Xiphactinus audax, a fish from the Cretaceous of Texas. University of Texas Bulletin No. 3201:87-92, 1 pl.
Walker, M.V. 1982. The Impossible Fossil. University Forum, Fort Hays State University 26: 4pp.

References

Bardack, D.. (1965). "Anatomy and evolution of chirocentrid fishes". The University of Kansas Paleontological Contributions.
(2016). "''Xiphactinus audax'' Leidy, 1870 from the Puskwaskau Formation (Santonian to Campanian) of northwestern Alberta, Canada and the distribution of ''Xiphactinus'' in North America". Vertebrate Anatomy Morphology Palaeontology.
(2013). "Osteology of ''Eubiodectes libanicus'' (Pictet & Humbert, 1866) and some other ichthyodectiformes (Teleostei): phylogenetic implications". Journal of Systematic Palaeontology.
[https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=35308 ''Xiphactinus''] at [[Fossilworks]].org
Haines, Tim. (2005). "The complete guide to prehistoric life". Firefly Books.
(1997). "''Xiphactinus vetus'' and the Distribution of ''Xiphactinus'' Species in the Eastern United States". [[Journal of Vertebrate Paleontology]].
(2016-02-04). "Xiphactinus audax Leidy 1870 from the Puskwaskau Formation (Santonian to Campanian) of northwestern Alberta, Canada and the distribution of Xiphactinus in North America". Vertebrate Anatomy Morphology Palaeontology.
(2020). "First record of the ichthyodectiform fish Xiphactinus (Teleostei) from Patagonia, Argentina". Alcheringa: An Australasian Journal of Palaeontology.
Carrillo-Briceño, J., Alvarado-Ortega, J. & Torres, C. (2012). [http://www.sbpbrasil.org/revista/edicoes/15_3/08_CarrilloBriceno_et_al.pdf Primer registro de ''Xiphactinus'' Leidy, 1870, (Teleostei: Ichthyodectiformes) en el Cretácico Superior de América del Sur (Formación La Luna, Venezuela)]. ''[[Revista Brasileira de Paleontologia]]'' 15(3):327-335
Konishi, T., Newbrey, M. G., & Caldwell, M. W. (2014). A small, exquisitely preserved specimen of ''Mosasaurus missouriensis'' (Squamata, Mosasauridae) from the upper Campanian of the Bearpaw Formation, western Canada, and the first stomach contents for the genus. Journal of Vertebrate Paleontology, 34(4), 802–819. https://doi.org/10.1080/02724634.2014.838573
(2019). "The smallest recorded specimen of ''Xiphactinus audax'' from the Niobrara Chalk of Kansas and its implications for juvenile ichthyodectid ecology". Historical Biology: An International Journal of Paleobiology.
Armstrong, John R. (1987). Creation/Evolution Newsletter 7 5:21; Geolog. 16, Part 4.
(2010-10-26). "Kansas Rep. Tom Sloan agrees to back X-fish as state's official fossil / LJWorld.com". .ljworld.com.
"State Fossils - Kansapedia - Kansas Historical Society".
"List of State Fossils". Fossilera.

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