paleonet Mosasaurs ate plesiosaurs

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Although the remains of a juvenile polycotylid plesiosaur as stomach contents of a large mosasaur (Tylosaurus) were first discovered by Charles Sternberg in 1918, his brief report did not receive much attention at the time, and the association went unnoticed. Fortunately, the two specimens were acquired by the United States National Museum (Smithsonian) where the mosasaur skeleton was placed on exhibit in 1921. I was able to examine the plesiosaur remains in late 2001 and described them in more detail in a paper just published in the latest volume of The Mosasaur:

Everhart, M. J. 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.

The full text of Sternberg’s 1922 report as well as additional pictures of the partially digested plesiosaur specimen are shown here:

http://www.oceansofkansas.com/sternberg22.html

In this case, the mosasaur was about 9 m long (estimated weight = 1100 kg / 2200 lb.) while the polycotylid was much smaller (about 2 m; 65 kg / 140 lb.); hardly a fair fight:

http://www.oceansofkansas.com/Pliosaurs/TYLODOLI.jpg

The juvenile polycotylid was certainly a large item to swallow, but well within the capabilities of a large Tylosaurus with its powerful bite and flexible (snakelike) skull and lower jaws. Although plesiosaurs had not been previously documented in the diet of mosasaurs, they should not be unexpected since Tylosaurus, in particular, is known to have consumed large fish, birds and other mosasaurs.

See: Martin, J. E. and P. R. Bjork, 1987. Gastric residues associated with a mosasaur from the late Cretaceous (Campanian) Pierre Shale in South Dakota, Dakoterra, 3:68-72).

See also: http://www.oceansofkansas.com/SDSMT.html (middle of page)

Regards,

Mike Everhart

Sternberg Museum of Natural History

Fort Hays State University