Tylosaurinae

Taxobox
name = Tylosaurines
fossil_range = Late Cretaceous

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image_width = 200px
image_caption = "Tylosaurus"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
ordo = Squamata
familia = Mosasauridae
subfamilia = Tylosaurinae
subfamilia_authority = Williston, 1895Williston, S. W. 1895. New or little-known extinct vertebrates. "Kansas University Quarterly" 6:95-98.]
subdivision_ranks = Genera
subdivision =
*"Hainosaurus"
*"Taniwhasaurus"
*"Tylosaurus"

Tylosaurinae Williston, S. W. 1897. Range and distribution of the mosasaurs with remarks on synonymy. "Kansas University Quarterly" 4(4):177-185.] is a subfamily of mosasaurs, a diverse group of Late Cretaceous marine lizards.

Russell (1967, pp. 170 Russell DA, 1967. Systematics and morphology of American mosasaurs. Peabody Museum of Natural History, Yale University, Bulletin 23.] ) defined the Tylosaurinae as follows: "Large rostrum present anterior to premaxillary teeth. Twelve or more teeth in dentary and maxilla. Cranial nerves X, XI, and XII leave lateral wall of opisthotic through a single foramen. No canal in basioccipital or basispehnoid for basilar artery. Suprastapedial process of quadrate moderately large, distally pointed. Dorsal edge of surangular rounded and longitudinally horizontal...Twenty nine presacral vertebrae present. Length of presacral series less than that of postsacral series in "Tylosaurus", neural spines of posterior caudal vertebrae at most only slightly elongated, do not form an appreciable fin. Haemal arches unfused to caudal centra. Appendicular elements lack smoothly finished articular surfaces."

Genera referrable to the Tylosaurinae (informally and collectively known as "tylosaurines" or "tylosaurs") have been found on all continents except Australia and South America. The etymology for the subfamily is derived from the genus of the type species, "Tylosaurus". In general, tylosaurs were large-bodied marine lizards armed with sturdy, conical teeth and an elongated premaxilla and extensions of the dentaries that do not bear teeth to the very end such as is found in other genera of mosasaurs. Cope's original concept of a "battering ram" snout is not supported by fossil evidence. Stomach contents from a tylosaur recovered in South DakotaMartin JE, Bjork PR. 1987. Gastric residues associated with a mosasaur from the late Cretaceous (Campanian) Pierre Shale in South Dakota. "Dakoterra" 3:68-72.] included remains of another mosasaur, a bony fish, the large, flightless seabird "Hesperornis", and possibly a shark, indicating that tylosaurs were generalists. Another specimen collected by Charles Sternberg Sternberg CH. 1922. Explorations of the Permian of Texas and the chalk of Kansas, 1918. Kansas Academy of Science, Transactions 30(1):119-120. (Papers - Fifty-first annual meeting, 1919), State Printer, Topeka.] included the bones of a small plesiosaur (see also Everhart MJ. 2004. Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a "Tylosaurus proriger" (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. "The Mosasaur" 7:41-46.] ).

Lingham-Soliar Lingham-Soliar T. 1992. The tylosaurine mosasaurs (Reptilia, Mosasauridae) from the upper Cretaceous of Europe and Africa. "Bulletin de L’Institut Royal des Sciences Naturelles de Belgique. Sciences de la Terre" 62:171-194.] suggested that tylosaurines were not among the fastest swimming nor the strongest mosasaurids. However, they are lightly built, having greatly reduced the weight of their bodies and possessing relatively small pectoral and pelvic girdles, fore- and hindlimbs. Their bone is highly cancellous and may have been impregated with fat cells during life, adding buoyancy. These traits suggest that tylosaurs may have been ambush predators. Tylosaurs were among the largest mosasaurs, with some species of "Tylosaurus" and "Hainosaurus" reaching lengths of 9-15+ meters, making them among the largest of all marine reptiles. A small species of "Tylosaurus" reported by Russell , "T. "zangerli" has since proven to be a juvenile individual of "T. proriger" 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.] . Everhart Everhart MJ. 2005a. "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.] erected a third species ("T. kansasensis") from the Smoky Hill Chalk.

Polcyn and Bell (2005, p. 322 Polcyn MJ, Bell GL Jr. 2005. "Russellosaurus coheni" n. gen., n. sp., a 92 million-year-old mosasaur from Texas (USA), and the definition of the parafamily Russellosaurina. "Netherlands Journal of Geosciences" 84(3): 321-333.] ) have erected a more inclusive clade, the parafamily Russellosaurina, which includes the "subfamilies Tylosaurinae and Plioplatecarpinae and their sister-clade containing the genera "Tethysaurus", "Russellosaurus", and "Yaguarasaurus"."

Tylosaurs first appear in the fossil record in the early Coniacian Everhart MJ. 2005b. Earliest record of the genus "Tylosaurus" (Squamata; Mosasauridae) from the Fort Hays Limestone (Lower Coniacian) of western Kansas. "Transactions" 108 (3/4): 149-155.] and persist well into the Maastrichtian, a period of approximately twenty million years.

Species and Taxonomy

*Tylosaurinae
**"Tylosaurus" (?paraphyletic)
***"T. proriger"
***"T. nepaeolicus"
***"T. kansasensis"
***"T. pembinensis"
***"T. saskatchewanensis"
***"T. ivoensis" (Possibly a species of "Taniwhasaurus" Caldwell MW, Konishi T, Obata I, Muramoto K. 2008. New species of "Taniwhasaurus" (Mosasauridae, Tylosaurinae) from the upper Santonian-lower Campanian (Upper Cretaceous) of Hokkaido, Japan. "Journal of Vertebrate Paleontology" 28 (2): 339-348.] )
**"Hainosaurus"
***"H. bernardi"
***"H. gaudryi"
**"Taniwhasaurus"
***"T. oweni" (="Tylosaurus haumuriensis")
***"T. mikasaensis"
***"T. antarcticus"

References

Further reading

*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 pp.
*Lindgren, J. et. Siverson, M. 2002."Tylosaurus ivoensis": a giant mosasaur from the early Campanian of Sweden. Royal Society of Edinburgh "Transactions: Earth Sciences" Vol. 93(1):73-93.
*Russell, D. A. 1970. The vertebrate fauna of the Selma Formation of Alabama, Part VII, The mosasaurs, "Fieldiana, Geology Memoirs" 3(7):369-380.