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.
Gasosaurus
The first and to date only fossils, albeit postcranial (missing the skull), were recovered in 1985 during the construction of a gas facility, which explains the dinosaur's unusual name. It consists of laterally compressed teeth, 4 cervical, 7 dorsal, 5 sacral, and 7 caudal vertebrae, both humeri, and highly abraded and reconstructed pelvic and hind limb material that includes the left ilium, left ischium, left pubis, left femur, left tibia and left fibula. The fossils were defined as the type species "Gasosaurus constructus" by the paleontologists Dong Zhiming and Tang Zilu.