Clidastes

Shown is a drawing from Williston (1898) that shows the skeletons of three common species of mosasaurs from Kansas; Clidastes propython, Platecarpus tympaniticus and Tylosaurus proriger. Although these three species are shown about the same size in the drawing, in life, Clidastes was the smallest (about 12-15 feet); Platecarpus was the next largest (about 24 feet) and Tylosaurus was the largest (30 plus feet):

AMNH FR 192. A complete skeleton of Clidastes liodontus on display at the American Museum of Natural History.