any of several extinct carnivorous marine lizards from the Cretaceous Period, having the limbs modified into broad, webbed paddles.

< Neo-Latin Mosasaurus (1823) genus name, equivalent to Latin Mosa the Meuse river (where a species was first discovered) + Neo-Latin -saurus -saur Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
mosasaur or mosasaurus (ˈməʊsəˌsɔː, ˌməʊsəˈsɔːrəs)
n , pl -saurs, -sauri
any of various extinct Cretaceous giant marine lizards of the genus Mosasaurus and related genera, typically having paddle-like limbs
[C18: from Latin Mosa the river Meuse (near which remains were first found) + -saur]
mosasaurus or mosasaurus (ˈməʊsəˌsɔː, ˌməʊsəˈsɔːrəs, -ˈsɔːraɪ)
[C18: from Latin Mosa the river Meuse (near which remains were first found) + -saur]

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
mosasaur   (mō'sə-sôr')  Pronunciation Key 
Any of various medium-sized to large extinct aquatic lizards of the genus Mosasaurus of the Cretaceous Period, having modified limbs that served as paddles for swimming. Mosasaurs were related to the modern monitor lizard, with which they share a similar skull structure.
The American Heritage® Science Dictionary
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Encyclopedia Britannica


extinct aquatic lizards that attained a high degree of adaptation to the marine environment and were distributed worldwide during the Cretaceous Period (144 million to 65 million years ago). The mosasaurs competed with other marine reptiles-the plesiosaurs and ichthyosaurs-for food, which consisted largely of ammonoids, fish, and cuttlefish. Many mosasaurs of the Late Cretaceous were large, exceeding 9 metres (30 feet) in length, but the most common forms were no larger than modern porpoises.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Instead a totally new group enters the sea-monster guild, the long-bodied sea lizards of the mosasaur family.
In reptiles, mosasaur jaws and teeth and their ecology are introduced for instance.
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