What is a Pliosaur?
These fossils come from an Inland Sea in the Late Cretaceous that covered a large portion of north america around 90 million years ago. The inland sea deposited a formation found in the western USA known as the Mancos, or Tropic Shale. Numerous types of fossils are found in this formation including, Baculites, Ammonites, Pliosaurs, Turtles, numerous species of Sharks, and a wide variety of crustaceans just to name a few. Below are some of the fossils I've come across in the Tropic.

Pliosaur I Discovered From The Tropic Shale In Southern Utah.	Eopolycotylus rankini A new species of plesiosaur I discovered in the summer of 2001, which was later named after me.
	Pliosaur Discovered in Summer of 2005.

External Paleo Links:

The Plesiosaur Directroy, Plesiousauria.com

A great resource for information on Plesiosaurs and Pliosaurs.

Oceans of Kansas website

Another great resource for information on Plesiosaurs and Pliosaurs, and a lot more information on the Tropic, Mancos shale.