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.
Goronyosaurus
Goronyosaurus is an extinct genus of marine lizard belonging to the mosasaur family. Fossils of "Goronyosaurus" are exclusively known from the Dukamaje Formation of Niger and Nigeria and are Maastrichtian in age. Its fossils were first described in the 1930s as Mosasaurus nigeriensis, but subsequent remains revealed a highly unique set of adaptations that prompted the species to be reclassified as the only species of the new genus "Goronyosaurus" in 1972. These unique adaptations have made "Goronyosaurus" notoriously difficult to classify within the Mosasauridae and it is often left out of phylogenetic analyses.