Mosasaur
Mosasaurs (from Latin "Mosa" meaning the 'Meuse river', and Greek σαύρος "sauros" meaning 'lizard') are an extinct group of large marine reptiles containing 38 genera in total. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-Pg event at the end of the Cretaceous period, about 66 million years ago.
Evolution of dinosaurs
The process leading up to the Dinosauromorpha and the first true dinosaurs can be followed through fossils of the early Archosaurs such as the Proterosuchidae, "Erythrosuchidae" and "Euparkeria" which have fossils dating back to 250 Ma, through mid-Triassic archosaurs such as "Ticinosuchus" 232-236 Ma. Crocodiles are also descendants of mid-Triassic archosaurs.