Tylosaurinae

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Tylosaurines
Fossil range: Late Cretaceous
Tylosaurus
Tylosaurus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Squamata
Family: Mosasauridae
Subfamily: Tylosaurinae
Williston, 1895
Genera

See text.

Tylosaurinae (Williston, 1895; Williston, 1897) is a subfamily of mosasaurs, a diverse group of Late Cretaceous marine lizards.

Russell (1967, pp. 170) 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."

Taniwhasaurus.
Taniwhasaurus.

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 teeth and a "battering ram" snout composed of the elongated premaxilla and dentaries. Stomach contents from a tylosaur recovered in South Dakota (Martin et Bjork, 1987) included remains of other mosasaurs, bony fish, the large seabird Hesperornis, and sharks, indicating that tylosaurs were generalists. Lingham-Soliar (1992) 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 (1967), T. "zangerli" has since proven to be a juvenile individual of T. proriger (Kiernan, 2002).

Polcyn and Bell (2005, p. 322) 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 Coniacian and persist well into the Maastrichtian, a period of approximately twenty million years.

[edit] Species and Taxonomy

[edit] References

  • 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.
  • 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.
  • 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.
  • 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.
  • Martin, J. E. and Bjork, P. R. 1987. Gastric residues associated with a mosasaur from the late Cretaceous (Campanian) Pierre Shale in South Dakota. Dakoterra 3:68-72.
  • Polcyn, M. J. et Bell, G. L., 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.
  • Russell, D. A., 1967. Systematics and morphology of American mosasaurs. Peabody Museum of Natural History, Yale University, Bulletin 23.
  • Russell, D. A. 1970. The vertebrate fauna of the Selma Formation of Alabama, Part VII, The mosasaurs, Fieldiana, Geology Memoirs 3(7):369-380.
  • Williston, S. W. 1895. New or little-known extinct vertebrates. Kansas University Quarterly 6:95-98.
  • Williston, S. W. 1897. Range and distribution of the mosasaurs with remarks on synonymy. Kansas University Quarterly 4(4):177-185.
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