Tylosaurus
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 An early etching of Tylosaurus
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Tylosaurus (Greek tylos "protuberance, knob" + Greek 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 Upper Cretaceous period. Tylosaurus proriger was among the largest of all the mosasaurs (along with Hainosaurus and Mosasaurus hoffmanni), reaching maximum lengths of 15 meters or more (49+ feet). 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 paleoenviroments, Tylosaurus seems to have preferred shallow, nearshore waters (as with the Eutaw Formation and Mooreville Chalk of Alabama), while favouring deeper water farther out from shore in other environments (as with the Niobrara Chalk of the western U.S.).
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[edit] Tylosaurus discovered
Like many other mosasaurs, the early history of this taxon is complex and involves the infamous rivalry between two American paleontologists, Edward Drinker Cope and Othniel Charles Marsh. Originally, the name "Macrosaurus" proriger was proposed by Cope for a fragmentary skull and thirteen vertebrae collected from the Kansas badlands and 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 reassigned Cope's holotype to another 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, for the original Harvard material as well as additional, more complete specimens which had also been collected from Kansas.
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 from 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.
[edit] How many 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), 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), from the late Coniacian of Kansas.
A closely related genus, Hainosaurus ("Haine lizard", named for 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, 1897) and are referred to informally as "tylosaurines" or "tylosaurs." Bell (1997) placed the tylosaurines together with the plioplatecarpine mosasaurs (Platecarpus, Plioplatecarpus, etc.) in an informal monophyletic grouping which he called the "Russellosaurinae."
[edit] References
- Bell, G. L. 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.
- Bell, G. L. 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.
- Cope, E. D. 1869. [Remarks on Macrosaurus proriger.] Proceedings of the Academy of Natural Sciences of Philadelphia 11(81), p. 123.
- Cope, E. D. 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), p. 3-48.
- Everhart, M. J. 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), p. 56-75.
- Everhart, M. J. 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), p. 33-43.
- Everhart, M. J. 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, M. J. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 322 pp.
- Everhart, M. J. 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), p. 231-240.
- Kiernan, C. R. 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.
- Marsh, O. C. 1872. Note on Rhinosaurus. Am. Jour. Sci. 4(20):147.
- Russell, D. A. 1967. Systematics and morphology of American mosasaurs (Reptilia, Sauria). Yale Univ. Bull. 23:241 pp.
- Novas, F. E., M. Fernández, Z. B. Gasparini, J. M. Lirio, H. J. Nuñez and P. Puerta. 2002. Lakumasaurus antarcticus, n. gen. et sp., a new mosasaur (Reptilia, Squamata) from the Upper Cretaceous of Antarctica. Ameghiniana, 39(2):245-249
- Schumacher, B. A. 1993. Biostratigraphy of Mosasauridae (Squamata, Varanoidea) from the Smoky Hill Chalk Member, Niobrara Chalk (Upper Cretaceous) of Western Kansas, Unpub. Masters Thesis, Fort Hays State University, 68 pp.
- Williston, S. W. 1898. Mosasaurs. The University Geological Survey of Kansas, Part V. 4:81-347, pls. 10-72.
