The story
Mosasaurs were marine lizards, relatives of monitor lizards and snakes. The earliest forms, descended from semi-aquatic aigialosaurs, appear about 98 million years ago, and after the great ichthyosaurs faded, mosasaurs spread across the world's seas. They had paddle limbs, a tail fin, and a double-hinged jaw with rows of teeth on the palate to hold slippery prey. Some, like Tylosaurus from Kansas, reached about 12 m. They gave live birth at sea.
Their discovery changed science. A giant skull from a chalk quarry near Maastricht in the Netherlands, found in the 1700s and seized by French troops in 1794, was analyzed by Georges Cuvier in 1808, who recognized a giant lizard related to monitors. It helped prove that species could go extinct. Conybeare named the genus Mosasaurus, Meuse lizard, in 1822. The mosasaurs vanished at the end of the Cretaceous with the asteroid impact, leaving the seas open for sharks and later whales.
Why it mattered
- The Maastricht skull helped establish extinction as a fact in the early 1800s.
- Mosasaurs filled the top predator niche in the Late Cretaceous seas.
- Their extinction cleared marine niches that sharks, toothed whales and sea turtles later filled.
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