October 29, 2010 : Mosasaur (Extinct)

Mosasaur

Mosasaurs (from Latin Mosa meaning the 'Meuse river', and Greek sauros meaning 'lizard') are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs are now considered to be the closest relatives of snakes, due to cladistic analyses that have taken into account similarities in jaw and skull anatomies. Mosasaurs were varanoids closely related to terrestrial monitor lizards. They probably evolved from semi-aquatic squamates known as aigialosaurs, which were more similar in appearance to modern-day monitor lizards, in the Early Cretaceous. During the last 20 million years of the Cretaceous Period (Turonian-Maastrichtian), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators.

Mosasaurs breathed air, were powerful swimmers, and were well-adapted to living in the warm, shallow epicontinental seas prevalent during the Late Cretaceous Period. Mosasaurs were so well adapted to this environment that they gave birth to live young, rather than return to the shore to lay eggs, as sea turtles do.

The smallest-known mosasaur was Carinodens belgicus, which was about 3.0 to 3.5 m long and probably lived in shallow waters near shore, cracking mollusks and sea urchins with its bulbous teeth. Larger mosasaurs were more typical: mosasaurs ranged in size up to 17 m. Tylosaurus holds the record for longest mosasaur, at 17.5 m.