Tylosaurus

Taxobox
name = "Tylosaurus"
fossil_range = Late Cretaceous

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image_width = 200px
image_caption =
regnum = Animalia
phylum = Chordata
classis = Sauropsida
ordo = Squamata
subordo = Scleroglossa
infraordo = Anguimorpha
familia = Mosasauridae
subfamilia = Tylosaurinae
genus = "Tylosaurus"
genus_authority = Marsh, 1872 Marsh OC. 1872. Note on "Rhinosaurus". "American Journal of Science" 4 (20): 147.]
subdivision_ranks = Species
subdivision =
* "T. proriger"
* "T. nepaeolicus"
* "T. haumuriensis"
* "T. kansasensis"
* "T. capensis"
* "T. pembinensis"
* "T. saskatchewanensis"

"Tylosaurus" (Greek "τυλος"/"tylos" "protuberance, knob" + Greek "σαυρος"/"sauros" "lizard") was a mosasaur, a large, predatory marine lizard closely related to modern monitor lizards and to snakes. Along with plesiosaurs, sharks, fish, and other genera of mosasurs, it was a dominant predator of the Western Interior Seaway during the Late Cretaceous. "Tylosaurus proriger" was among the largest of all the mosasaurs (along with "Hainosaurus" and "Mosasaurus hoffmannii"), reaching maximum lengths of 15 meters or more (49+ ft). A distinguishing characteristic of "Tylosaurus" is its elongated, cylindrical premaxilla (snout) from which it takes its name and which may have been used to ram and stun prey and also in intraspecific combat. Stomach contents associated with specimens of "Tylosaurus proriger" indicate that this ferocious mosasaur had a varied diet, including fish, sharks, smaller mosasaurs, plesiosaurs, and flightless diving birds such as "Hesperornis". In some paleoenvironments, "Tylosaurus" seems to have preferred shallow, nearshore waters (as with the Eutaw Formation and Mooreville Chalk of Alabama), while favoring deeper water farther out from shore in other environments (as with the Niobrara Chalk of the western U.S.).

Discovery

Like many other mosasaurs, the early history of this taxon is complex and involves the infamous rivalry between two early American paleontologists, Edward Drinker Cope and Othniel Charles Marsh. Originally, the name "Macrosaurus" proriger" was proposed by Cope Cope ED. 1869. [Remarks on "Macrosaurus proriger".] "Proceedings of the Academy of Natural Sciences of Philadelphia" 11(81): 123.] for a fragmentary skull and thirteen vertebrae collected from near Monument Rocks in western Kansas in 1868. It was placed in the collections of the Harvard Museum of Comparative Zoology. Only a year later, Cope redescribed the same material in greater detail and referred it, instead, to the English mosasaur taxon "Liodon". Then, in 1872, Marsh named a more complete specimen as a new genus, "Rhinosaurus" ("nose lizard"), but this name soon proved to be preoccupied. Cope suggested that "Rhinosaurus" be replaced by yet another new name, "Rhamposaurus" which also proved to be preoccupied. Marsh finally erected "Tylosaurus" later in 1872, to include the original Harvard material as well as additional, more complete specimens which had also been collected from Kansas. A giant specimen of "T. proriger", recovered in 1911 by C. D. Bunker near Wallace, Kansas is one of the largest skeleton of "Tylosaurus" ever found. It is currently on display at the University of Kansas Museum of Natural history.

In 1918, Charles H. Sternberg found a "Tylosaurus", with the remains of a plesiosaur in its stomach. [http://www.oceansofkansas.com/Tylo-prey.html] The specimen is currently mounted in the United States National Museum (Smithsonian) and the plesiosaur remains are stored in the collections. Although these important specimens were briefly reported by C. H. Sternberg (1922), the information was lost to science until 2001. This specimen was rediscovered and described by Everhart (2004a). It is the basis for the story line in the new (2007) National Geographic IMAX movie - Sea Monsters, and a book by the same name (Everhart, 2007). Note that the "early photograph" of a "Tylosaurus skull" (above) was taken by George F. Sternberg about 1926 after he collected and prepared the specimen. It was discovered in the Smoky Hill Chalk of Logan County, Kansas. Sternberg offered the specimen to the Smithsonian and included this photograph in his letter to Charles Gilmore. Copies of the original photos are in the archives of the Sternberg Museum of Natural History (FHSM). The specimen is FHSM VP-3, the exhibit specimen in the same museum.

Species

Though many species of "Tylosaurus" have been named over the years, only a few are now recognized by scientists as taxonomically valid. They are as follows: "Tylosaurus proriger" (Cope, 1869), from the Santonian and lower to middle Campanian of North America (Kansas, Alabama, Nebraska, etc.); "Tylosaurus nepaeolicus" (Cope, 1874 Cope ED. 1874. Review of the vertebrata of the Cretaceous period found west of the Mississippi River. "U. S. Geological Survey of the Territories, Bulletin" 1 (2): 3-48.] ), from the Santonian of North America (Kansas); "Tylosaurus haumuriensis" (Hector, 1874; ="Taniwhasaurus oweni"), from the lower to middle Campanian of New Zealand; "Tylosaurus kansasensis" Everhart, 2005 Everhart MJ. 2005. "Tylosaurus kansasensis", a new species of tylosaurine (Squamata: Mosasauridae) from the Niobrara Chalk of western Kansas, U.S.A. "Netherlands Journal of Geosciences / Geologie en Mijnbouw" 84 (3): 231-240.] , from the late Coniacian of Kansas.

A closely related genus, "Hainosaurus" ("Haine lizard", named after the Haine River in Belgium) is known from the Creatceous of North America and Europe. Both "Tylosaurus" and "Hainosaurus" are grouped together into the subfamily Tylosaurinae Williston SW. 1898. Mosasaurs. "The University Geological Survey of Kansas, Part V". 4: 81-347 (pls. 10-72).] and are referred to informally as "tylosaurines" or "tylosaurs." Bell Bell GL. Jr. 1997. A phylogenetic revision of North American and Adriatic Mosasauroidea. pp. 293-332 In: Callaway J. M. and E. L Nicholls, (eds.), "Ancient Marine Reptiles", Academic Press, 501 pages.] placed the tylosaurines together with the plioplatecarpine mosasaurs ("Platecarpus", "Plioplatecarpus", etc.) in an informal monophyletic grouping which he called the "Russellosaurinae."

In Popular culture

* "Tylosaurus" appeared in the BBC documentary Sea Monsters (revealed in the encyclopedia). It was the apex predator in what they considered "the most deadly sea ever" (the Cretaceous).
* In the National Geographic documentary, , "Tylosaurus" once again is depicted as the apex predator of the Late Cretaceous seas of North America. By that time (Early Campanian, ~82 ma), mosasaurs were the largest predators living in the Earth's oceans.

References

Further reading

Bell GL. Jr. 1997. Part IV: Mosasauridae - Introduction. pp. 281-292 In: Callaway J. M. and E. L Nicholls, (eds.), "Ancient Marine Reptiles", Academic Press, 501 pages.

Everhart MJ. 2001. Revisions to the biostratigraphy of the Mosasauridae (Squamata) in the Smoky Hill Chalk Member of the Niobrara Chalk (Late Cretaceous) of Kansas. "Kansas Academy of Science, Transactions" 104 (1-2): 56-75.

Everhart MJ. 2002. New data on cranial measurements and body length of the mosasaur, "Tylosaurus nepaeolicus" (Squamata; Mosasauridae), from the Niobrara Formation of western Kansas. "Kansas Academy of Science, Transactions" 105 (1-2): 33-43.

Everhart MJ. 2005. Earliest record of the genus "Tylosaurus" (Squamata; Mosasauridae) from the Fort Hays Limestone (Lower Coniacian) of western Kansas. "Transactions" 108 (3/4): 149-155.

Everhart MJ. 2005. "Oceans of Kansas - A Natural History of the Western Interior Sea". Indiana University Press, 322 pp.

Kiernan CR. 2002. Stratigraphic distribution and habitat segregation of mosasaurs in the Upper Cretaceous of western and central Alabama, with an historical review of Alabama mosasaur discoveries. "Journal of Vertebrate Paleontology" 22 (1): 91-103.

Russell DA. 1967. Systematics and morphology of American mosasaurs (Reptilia, Sauria). "Yale Univ. Bull." 23: 241 pp.

Novas FE, Fernández M, Gasparini ZB, Lirio JM, Nuñez HJ, Puerta P. 2002. "Lakumasaurus antarcticus", n. gen. et sp., a new mosasaur (Reptilia, Squamata) from the Upper Cretaceous of Antarctica. "Ameghiniana" 39 (2): 245-249.

External links

* [http://www.oceansofkansas.com/index.html Oceans of Kansas; includes much additional information and many illustrations and photographs of tylosaurines, including restorations and skeletons.]

* [http://www.oceansofkansas.com/Cope1869b.html E.D. Cope's original description of "Macrosaurus proriger" from western Kansas, with the published figure (1870) and recent photographs.]