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Megalneusaurus is an extinct genus of large pliosaur that lived in the Sundance Sea during the Kimmeridgian, ~156-152 million years ago, in the Late Jurassic. It was named by paleontologist W. C. Knight in 1895.

Temporal range: 156.2–152 Ma
Late Jurassic
Scientific classification

W. C. Knight, 1898
Binomial name
Megalneusaurus rex
(W. C. Knight, 1895)
Illustration of some of the holotype fossils

The genus and type species was based upon ribs, vertebrae, a fore-paddle and fragments of the pectoral girdle discovered in Wyoming, USA in 1895.[1] The species named as Megalneusaurus rex (meaning "great swimming lizard King") in 1898.[2] However some of this material has since been lost, although new material has been discovered from the same site.[3] Based upon the bones very large size, it appears to have grown to a size comparable to Liopleurodon.

Material from southern Alaska have been referred to Megalneusaurus, although this material is from an individual of much smaller size.[4]


Megalneusaurus is said to reach lengths of 7.6–9.7 m (25–32 ft), though there are some estimates that propose a length of 11 meters.[5]


Megalneusaurus hunted in the warm waters of the Sundance Sea some 150 million years ago. The large, inland sea hosted a wide array of marine reptiles.[6]


While no stomach contents of Megalneusaurus have been discovered, it is reasonable to assume that it ate medium-sized marine reptiles such as the ichthyosaur Ophthalmosaurus, and the cryptoclidid plesiosaur Pantosaurus.[citation needed]

See alsoEdit


  1. ^ Knight WC. 1895 A new Jurassic plesiosaur from Wyoming. Science 2: 449.
  2. ^ Knight WC. 1898. Some new Jurassic vertebrates from Wyoming. American Journal of Science 4: 378-381.
  3. ^ Wahl WR, Ross M, Massare JA. 2007. Rediscovery of Wilbur Knight’s Megalneusaurus rex site: new material from an old pit. Paludicola 6 (2): 94-104.
  4. ^ Weems RE, Blodgett RB. 1996. The pliosaurid Megalneusaurus: a newly recognized occurrence in the Upper Jurassic Neknek Formation of the Alaska Peninsula. U.S. Geological Survey Bulletin 2152: 169-175.
  5. ^
  6. ^ "Mesozoic Stratigraphy in the Thermopolis Area". Big Horn Basin Foundation. Retrieved 2007-02-06