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. It is 21 inches long and 9 inches wide. The smallest-known mosasaur was Dallasaurus turneri, which was less than a 1 meter (3.3 ft) long. Larger mosasaurs were more typical: Hainosaurus holds the record for the longest mosasaur, at 17.5 meters (57 ft). Mosasaurs (from Latin Mosa meaning the 'Meuse river', and Greek σαύρος sauros meaning 'lizard') are large, extinct, marine reptiles. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from semiaquatic squamates[1] 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 decline of plesiosaurs, mosasaurs became the dominant marine predators.