Mosasaurinae
Plioplatecarpinae
Tylosaurinae
A mosasaur was not a dinosaur, but rather an ocean-dwelling serpentine marine reptile related to varanids like monitor lizards. These predators evolved from terrestrial ancestors in the early Cretaceous and dominated the oceanic food chain during the late Cretaceous Period.

Genera included Mosasaurus, Tylosaurus, and Platecarpus.

Description

Mosasaurs breathed air, but were powerful swimmers, so well adapted to living in shallow seas that they gave birth to live young, rather than return to the shoreline to lay eggs, as sea turtles do.

The smallest known mosasaur is Carinodens belgicus, which was about 3 to 3.5 m long and probably lived on the sea floor cracking mollusks and sea urchins with its bulbous teeth. Larger mosasaurs were more typical: mosasaurs ranged in size up to 17 m: Hainosaurus holds the record for longest mosasaur, at 17.5 m.

A mosasaur had a body form similar to that of a crocodile, although streamlined for fast swimming in marine waters. Their front leg bones were reduced in length, their paddles strengthened by long finger-bones. Their rear legs were atrophied. Their powerful tails, lashed side to side crocodile-fashion, provided locomotion.

Mosasaurs had a loosely-hinged jaw which enabled them to gulp down their prey almost whole, a snakelike habit that has helped identify the stomach contents fossilized within a Mosasaur skeleton, which included the diving seabird Hesperornis, a marine bony fish, a shark, and part of a smaller mosasaur. Mosasaur bones have been found with embedded shark teeth.

Environment

Sea-levels were high during the Cretaceous, causing marine ingressions in many parts of the world, and a great inland seaway in North America. Mosasaur fossils have been found in the Netherlands and Sweden, in Africa, in Australia, New Zealand, and Vega Island off the coast of Antartica. In Canada and the United States, complete or partial specimens have been found in Alabama and Georgia and in almost all the states covered by the seaway: Texas, southwest Arkansas, New Mexico, Kansas, Colorado, the Dakotas and Montana.

The "dinosaurs" of New Zealand, a volcanic island arc that has never been part of a continent, are a unique series of mosasaurs and plesiosaurs, another group of predatory marine reptiles of the Mesozoic era.

Discovery

The first publicized discovery of a fossil mosasaur preceded any dinosaur fossil discoveries, and drew The Enlightenment's attention to the existence of fossilized animals; the specimen was discovered in 1780 by quarry-workers in a subterranean gallery who quickly alerted Doctor C. K. Hoffman , a surgeon of Maastricht and fossil-hunter though rights of ownership lay with a canon of Maastricht, as owner of the overlying land.

Dr. Hoffman's correspondence among men of science made the find famous. When the Revolutionary forces occupied Maastricht, the carefully-hidden fossil was uncovered, betrayed, it is said, by a case of wine, and transported to Paris, where Georges Cuvier was able to describe it for science, though le grand animal fossile de Maastricht was not described as a Mosasaur ("Meuse reptile") until 1822, and not given its official name, Mosasaurus hoffmani, until 1829. A Mosasaur skull that had actually been discovered at Maastricht earlier, has recently been reidentified in the Teylers Museum, Haarlem.

The Maastricht limestone beds were rendered so famous they have given their name to the ulimate 6-million-year epoch of the Cretaceous: the Maastrichtian .

External links

• BBC Science and Nature: Mosasaurs
• Mike Everhart and David Lewis, "Mesozoic marine monsters of the Mangahouanga": New Zealand fossil fauna
• Mike Everhart, "A day in the life of a Mosasaur": life in the Sea of Kansas, illus. by Carl Buell
• Mike Everhart, "Mosasaurus hoffmani" until 1829.
• Mosasaurus maximus mounted skeleton at University of Texas Memorial Museum