Xiphactinus

Xiphactinus (from Latin and Greek for "sword-ray") is an extinct genus of large (4.5 to 6 metres (15 to 20 ft)) predatory marine bony fish that lived during the Late Cretaceous (Albian to Maastrichtian).[3] When alive, the fish would have resembled a gargantuan, fanged tarpon (to which it was, however, not related).[4] The species Portheus molossus described by Cope[4] 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),[1][5] and Cretaceous formations all over the East Coast (most notably Georgia, Alabama, North Carolina, and New Jersey) in the United States,[1] as well as Europe, Australia[6], the Kanguk and Ashville Formations of Canada,[1] and La Luna Formation of Venezuela.[1][7]

Xiphactinus
Temporal range: Albian–Maastrichtian
~112–66 Ma
Xiphactinus fossil from the National Museum of Natural History
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Ichthyodectiformes
Family: †Ichthyodectidae
Subfamily: †Ichthyodectinae
Genus: †Xiphactinus
Leidy, 1870
Species
  • X. audax Leidy 1870[1]
  • X. vetus Leidy 1856[2]
Synonyms

Portheus molossus Cope, 1871

Paleobiology
Xiphactinus swimming
Xiphactinus audax restoration
Gillicus arcuatus within the stomach of Xiphactinus audax, George F. Sternberg's most famous fossil find.

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 13 feet (4.0 m) fossil specimen was collected by George F. Sternberg with another, nearly perfectly preserved 6 feet (1.8 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 can be seen at the Sternberg Museum of Natural History in Hays, Kansas.[4][8]

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.

Virtually nothing is known about the larval or juvenile stages. The smallest fossil specimen of X. audax consists of a tooth bearing premaxilla and lower jaws of an individual estimated to be about 12 inches (30 cm) long.[4][9]

The species and all other ichthyodectids became extinct near the end of the Late Cretaceous – see Cretaceous–Paleogene extinction event.

An incomplete skull of what may be a new species of Xiphactinus was found in 2002 in the Czech Republic, in a small town called Šachov next to Borohrádek city, by 16-year-old student Michal Matějka.

In July 2010 the bones of a Xiphactinus were discovered near Morden, Manitoba, Canada. The specimen was about 6 metres (20 ft) long and was found with the flipper of a mosasaur between its jaws.[10]

"Unicerosaurus"
Xiphactinus compared to other ichthyodectids

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".[11] 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 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.[12]

References
  1. Xiphactinus at Fossilworks.org
  2. Schwimmer, David R.; Stewart, J. D.; Williams, G. Dent (1997). "Xiphactinus vetus and the Distribution of Xiphactinus Species in the Eastern United States". Journal of Vertebrate Paleontology. 17 (3): 610–15. doi:10.1080/02724634.1997.10011007. JSTOR 4523841.
  3. Sepkoski, Jack (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on July 23, 2011. Retrieved 2009-02-27.
  4. "Xiphactinus audax Leidy"
  5. Haines, Tim; Chambers, Paul (2005). The complete guide to prehistoric life (First ed.). Buffalo, N.Y.: Firefly Books. p. 134. ISBN 978-1-55407-181-4. The first Xiphactinus fossil was found during the 1850s in Kansas.
  6. "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. 1. 2016-02-04. doi:10.18435/B5H596.
  7. Carrillo-Briceño, J., Alvarado-Ortega, J. & Torres, C. (2012). 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
  8. "Xiphactinus Audax" (JPG). Sternberg Museum of Natural History. (archived: oceansofkansas.com).
  9. "Xiphactinus Audax" (JPG). oceansofkansas.com.
  10. "Major Fossil Discovery Underway in Morden" (PDF). Canadian Fossil Discovery Centre. July 16, 2010. Press release.
  11. Armstrong, John R. (1987). Creation/Evolution Newsletter 7 5:21; Geolog. 16, Part 4.
  12. "Kansas Rep. Tom Sloan agrees to back X-fish as state's official fossil / LJWorld.com". .ljworld.com. Associated Press. 2010-10-26. Retrieved 2011-10-12.


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