Xiphactinus

Xiphactinus

Xiphactinus audax Fossil range: Late Cretaceous
Xiphactinus audax specimen (FHSM VP-333) at the Sternberg Museum of Natural History.
Scientific classification
Class:	Actinopterygii
Superorder:	Osteoglossomorpha
Order:	Ichthyodectiformes
Family:	Ichthyodectidae
Subfamily:	Ichthyodectinae
Genus:	Xiphactinus
Species:	X. audax X. vetus

"The head was as long or longer than that of a fully grown grizzly bear, and the jaws were deeper in proportion to their length. The muzzle was shorter and deeper than that of a bull-dog. The teeth were all sharp cylindric fangs, smooth and glistening, and of irregular size. At certain distance in each jaw they projected three inches above the gum, and were sunk one inch into the jaw margin, being thus as long as the fangs of a tiger, but more slender. Two such fangs crossed each other on each side of the middle of the front. Besides the smaller fishes, the reptiles no doubt supplied the demands of his appetite."

—E.D. Cope

Xiphactinus audax (from Latin and Greek for "sword-ray") was a large, 4.5 to 5 m (15 to 20 feet) long predatory bony fish that lived in the Western Interior Sea, over what is now the middle of North America, during the Late Cretaceous. When alive, the fish would have resembled a gargantuan, fanged tarpon (to which it was, however, not related). Portheus molossus Cope is a junior synonym of the species. Skeletal remains of Xiphactinus have come from Kansas, Alabama, and Georgia; Europe and Australia.

History

A long fragment of a pectoral fin of Xiphactinus audax (USNM 52), collected by Dr. George M. Sternberg.

While the name Xiphactinus has been around since 1870, there has been considerable confusion over which name is actually correct. In 1870, Joseph Leidy named the fish from a 16 inch (40 cm) long fragment of a pectoral fin (USNM 52 - right), collected by Dr. George M. Sternberg, a year before E. D. Cope gave the name of Portheus molossus to a collection of several nearly complete specimens found near Fort Wallace. Leidy's name is correct by virtue of being the first to be published, but Cope's name was more popular and is still in use in many collections of Cretaceous fish.

Leidy (1856) gave a short description of a single tooth found in the Cretaceous marl of New Jersey and named it Polygonodon vetus:

"Based on a specimen of the crown of a tooth found in the marl (cretaceous) of Burlington County by L. T. Germain, Esq., Length three times the breadth; transverse section elliptical; with trenchant borders; with six planes on one side and seven on the other. Length 1½ inches, breadth ½ an inch. May be an incisor of Mososaurus [sic]?"

Leidy (1865) described the tooth in greater detail and included three figures (left) showing what it looked like in (12) posterior, (13) external view, and in cross section. Still believing the tooth to be reptilian, he thought it "may have belonged to Discosaurus or Cimoliasaurus, but the matter must be left for future determination."

The tooth was later determined to be from a sister species of Xiphactinus audax, raising the issue of which genus name should have priority... Polygonodon Leidy 1856 or Xiphactinus Leidy 1870? See Schwimmer, et al. (1997) for a more detailed explanation. Most likely it will remain Xiphactinus.

Paleobiology

A photograph of a disarticulated shark specimen (KUVP 247) at the University of Kansas Museum of Natural History. Inside are the remains of a large Xiphactinus audax inside the shark when it died. Note the large lower jaw, with teeth, in the upper center of this picture. Xiphactinus ribs are also scattered among the shark vertebrae.

The famous "fish-within-a-fish" Xiphactinus audax specimen (FHSM VP-333) at the Sternberg Museum of Natural History. The stomach contents (a large Gillicus arcuatus) is curated as FHSM VP-334. The Xiphactinus is just over 13 feet long. Scientists believe the struggling prey ruptured an organ of its captor as it was swallowed, killing the larger fish.

Skull of Xiphactinus audax.

Xiphactinus audax tooth from the Mount Laurel Formation.

Xiphactinus audax was a voracious predator fish. At least dozen specimens have been collected the remains of large, undigested or partially digested prey in their stomachs. In particular, one 13 feet (4.0m) 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 due to the smaller fish prey 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.

The most impressive part of a Xiphactinus is its rather bulldog-like expression, with its upturned jaw and giant, fang-like teeth. The jaw was very mobile, capable of opening wide to take in large-sized prey.

Xiphactinus' pectoral fins were held out by solid bony fin rays, giving the appearance of wings. Its body was long -- fifteen to twenty feet -- and there were more than 100 vertebrae along its backbone. Its tail was deep and forked, attached to the body at a narrow base. All of these attributes indicate that Xiphactinus was an extremely fast, powerful swimmer and an active, efficient predator.

Like many other species in the Late Cretaceous oceans, a dead or injured X. audax 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 their 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.

The species went extinct near the end of the Late Cretaceous as the Western Interior Seaway began to recede from the middle of North America along with all the other ichthyodectids - see Cretaceous–Tertiary 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 Sachov next Borohradek city, by student Michal Matejka.

Although it is known that Xiphactinus grew to be very large as adults, we know very little about them as juveniles.

References:

• Xiphactinus page - Oceans of Kansas

• Bardack, D. 1965. Anatomy and evolution of Chirocentrid fishes. University of Kansas Paleontological Contributions, Article 10, 88 pp. 2 pl.

• 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.

• Cope, E. D. 1872d. On the families of fishes of the Cretaceous formation in Kansas. Proceedings of the American Philosophical Society 12(88):327-357.

• 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 fossil fishes called by Professor Cope, Portheus, by Dr. Leidy, Xiphactinus. Zoological Bulletin 2(1): 25-54.

• 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. 1865. Cretaceous reptiles of the United States. Smithsonian Contributions to Knowledge 14(6):1-135, pls. I-XX. (Three figures and a more detailed description of the tooth of Polygonodon (Xiphactinus) vetus Leidy 1856)

• Leidy, J. 1870. [Remarks on ichthyodorulites and on certain fossil Mammalia.]. Proc. Acad. Nat. Sci. Phil. 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).

• Osborn, H. F. 1904. The great Cretaceous fish Portheus molossus Cope. Bull. Mus. Nat. Hist. Vol. 20, Art. 31, pp. 377-381, pl. 10. [AMNH 322199]

• Rogers, K., 1991. A dinosaur dynasty: The Sternberg fossil hunters, Mountain Press Publishing Company, 288 pages.

• Schwimmer, D. R., J. D. Stewart, and G. D. Williams. 1997. Xiphactinus vetus and the distribution of Xiphactinus species in the eastern United States. Journ. Vert. Paleo. 17(3):610-615.

• 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.

• Sternberg, C. H. 1917. Hunting Dinosaurs in the Badlands of the Red Deer River, Alberta, Canada. Published by the author, San Diego, Calif., 261 pp.

• Sternberg, C. H. 1922. Field work in Kansas and Texas. Kansas Academy of Science, Transactions 30(2):339-348.

• 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."

• Stewart, A. 1899. Notice of three new Cretaceous fishes, with remarks on the Saurodontidae Cope. Kansas Univ. Quar. 8(3):107-112. (Xiphactinus, Protosphyraena gigas and Empo (Cimolichthys))

• Stewart, A. 1900. Teleosts of the Upper Cretaceous. The University Geological Survey of Kansas. Topeka 4:257-403, 6 figs., pls. 33-78.

• Stovall, J. W. 1932. Xiphactinus audax, a fish from the Cretaceous of Texas. University of Texas Bulletin No. 3201:87-92, 1 pl.

• Thorpe, M. R. 1934. A new mounted specimen of Portheus molossus Cope. American Journal of Science, 5th series, 28(164):121-126, 2 fig.

• Walker, M.V. 1982. The Impossible Fossil. University Forum, Fort Hays State University 26: 4pp.

• Walker, M.V. 2006. The impossible fossil - Revisited. Kansas Academy of Science, Transactions 109 (1/2), p. 87-96.