Mosasaurs were huge, serpentine (snake-like) marine reptiles. They were not dinosaurs, but were linked to snakes and monitor lizards.
Mosasaurs were commanding swimming reptiles that had adapted to living in shallow seas. These carnivores (meat-eaters) motionless breathed air. They were a short-lived line of reptiles that went died out during the K-T extinction, 65 million years past.
Some Mosasaurs include the Mosasaurus (40-59 feet long with jagged teeth from the North Atlantic), Platecarpus, Tylosaurus (33-40 feet long with jagged teeth, from the North and Plotosaurus, Clidastes, Plioplatecarpus and Globidens (with smooth teeth for crushing shellfish).
The first Mosasaur discovered, Mosasaurus hoffmani, was establish in the Netherlands in 1780. These predators evolved from semi-aquatic squamates known as the aigialosaurs, close relations of modern-day monitor lizards, in the premature Cretaceous Period.
During the final 20 million years of the Cretaceous Period, with the extinction of the last ichthyosaurs and the refuse of the Cretaceous plesiosaurs and pliosaurs, mosasaurs became the dominant nautical predators. They were well-adapted to living in the warm, shallow epicontinental seas widespread during the Late Cretaceous Period.
Mosasaurs had a body shape alike to that of contemporary monitor lizards (varanids), but were more elongated and streamlined for swimming. Their long head had very pointed, potent jaws with many sharp teeth. Mosasaurs had four little, paddle-like limbs adapted to life in the water. A long tail, perhaps finned, concluded its serpentine body. Their limb bones were reduced in length and their paddles were shaped by webbing between their elongated digit-bones. Their tails were large and supplied the locomotor power.
This method of locomotion may have been alike to that used by the conger eel or sea snakes today. The animal may have lurked and pounced quickly and powerfully on passing prey, rather than hunting for it. Mosasaurs had a double-hinged jaw and elastic skull (much like that of a snake), which enabled them to gulp down their prey nearly whole.
Mosasaurs were carnivores, hunting and consumption fish, turtles, mollusks and shellfish. Fossil ammonites have been establish with many telltale Mosasaur toothprints in their shells, indicating that Mosasaurs frequent bit these hard-shelled animals in order to break their shell and get to the soft animal protein.
The various mosasaurs went extinct during the K-T extinction, 65 million years back. Mosasaurs were so well customized to living in shallow epicontinental seas that they gave birth to live young, rather than return to the shore, as ocean turtles do, to lay eggs.
The initial fossil remains were discovered at the Meuse river about 1780.