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Temporal range: 156.2–152 Ma
Late Jurassic
Scientific classification
Binomial name
Megalneusaurus rex

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.

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 also[edit]


  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