ple·​si·​o·​saur ˈplē-sē-ə-ˌsȯr How to pronounce plesiosaur (audio)
: any of an order or suborder (Plesiosauria) of large carnivorous marine reptiles of the Mesozoic with dorsoventrally flattened bodies and limbs modified into flippers

Examples of plesiosaur in a Sentence

Recent Examples on the Web This ancient marine environment had produced fossils of plesiosaurs and dolphin-like ichthyosaurs in other locations, so the researchers expected that any new find was going to be something similar. Jeanne Timmons, Ars Technica, 25 Jan. 2023 Originally thought to be saltwater animals only, recent research indicates that some plesiosaurs could live in freshwater environments (like Loch Ness). Stephen C. George, Discover Magazine, 23 Jan. 2024 This fearsome creature was not the largest animal of the tropical Cretaceous oceans: It was outclassed by several species of enormous long-necked plesiosaurs, such as the 26-foot-long Callawayasaurus colombiensis. Santiago Flórez, Smithsonian Magazine, 6 Feb. 2024 This has only added to the conviction that Nessie is either some surviving example of plesiosaur or a heretofore unknown species descended from those early dinosaurs. Stephen C. George, Discover Magazine, 23 Jan. 2024 Large amounts of plankton-eating fish died off as a result, leaving mosasaurs and plesiosaurs to face eventual extinction due to a shortage of nourishment. Jack Knudson, Discover Magazine, 22 Dec. 2023 Also part of Sotheby’s auction was a fossil of a plesiosaur, a marine reptile that lived in the Jurassic Period. David Chiu, Peoplemag, 19 Sep. 2023 Of course, many still hold out hope for the possibility of a somehow still undiscovered pod of plesiosaurs calling Loch Ness home. Andrew Paul, Popular Science, 24 Aug. 2023 The plesiosaur, a long-extinct marine reptile, lived in the lower Jurassic Period, about 200 million years ago, and is thought to have inspired the legend of the Loch Ness Monster, a mythical creature in Scottish folklore that was believed to live in a lake in the Scottish Highlands. Julia Jacobo, ABC News, 12 July 2023

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'plesiosaur.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


ultimately from Greek plēsios close (akin to Greek pelas near) + sauros lizard

First Known Use

1839, in the meaning defined above

Time Traveler
The first known use of plesiosaur was in 1839

Dictionary Entries Near plesiosaur

Cite this Entry

“Plesiosaur.” Dictionary, Merriam-Webster, Accessed 28 May. 2024.

Kids Definition


: any of a group of large Mesozoic marine reptiles with flattened bodies and limbs changed into paddles

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