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Modern reconstruction of Platecarpus tympaniticus showing crescent-shaped tail fluke

Mosasaurs were large, predatory marine lizards of the Upper Cretaceous. The first fossil Mosasaur, Mosasaurus hoffmanni, was found in the Netherlands in 1776.^p7 It was named in 1822 by W.D. Conybeare.

For the last 20 million years of the Cretaceous period after the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct at the K-Pg event at the end of the Cretaceous period, about 66 million years ago.