Mosasaurus ne irin HALITTAR (ma'ana misali) na mosasaurs, wani dadadden kungiyar na cikin ruwa squamate dabbobi masu rarrafe. Yana rayu daga game da 82 zuwa 66 da miliyan shekaru da suka wuce a lokacin da Campanian da Maastrichtian saukarwa daga Late Cretaceous. An gano burbushin Mosasaurus na farko da aka sani da kimiyya a matsayin kokon kai a cikin dutse na alli kusa da garin Maastricht na kasar Holland a karshen karni na 18, wanda da farko ake zaton kasusuwan kada ko dabbobin ruwa. Skaya daga cikin kwanyar da aka gano a kusa da 1780, wanda Faransa ta kwace a lokacin Yaƙin Juyin Juya Halin Faransa don ƙimar kimarta, an shahara da "babban dabba na Maastricht". A shekara ta 1808, masanin halitta Georges Cuvier ya kammala cewa mallakar wata katuwar ruwan teku ce mai kamanceceniya don sa ido kan kadangare amma in ba haka ba sabanin kowane sanannen dabba mai rai. Wannan ra'ayi ya kasance juyin-juya hali a lokacin kuma ya taimaka wajen tallafawa ra'ayoyin ɓarna na lokacin. Koyaya, Cuvier bai sanya sunan kimiyya ga sabuwar dabba ba;