Download or read book North American Plesiosaurs: Elasmosaurus, Cimoliasaurus, and Polycotylus written by Samuel Wendell Williston and published by Good Press. This book was released on 2022-01-06 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a detailed study of the Plesiosaurs, a group of giant, long-necked marine reptiles that belong to the order Plesiosauria. These animals emerged in the Late Triassic period and became especially predominant during the Jurassic period.