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.
Marasuchus
Until 2003 "Marasuchus" was thought to be one of the closest relatives of the dinosaurs. At present it has been supplanted by other dinosauromorphs such as "Silesaurus". Nonetheless, "Marasuchus" remains an important animal for understanding the origin and evolution of dinosaur characteristics. The following is a 
cladogram of basal Dinosauriformes according to Nesbitt (2011), and Dinosauria according to Baron "et al." (2017):
Alfred Romer first discovered fossils of the species in the 1960s in the Chañares Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina, all parts of the reptile’s skeletal anatomy are known from fossils except for the skull and lower jaw. The formation was dated as being 235 to 234 million years old.