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.
Massospondylus
The first fossils of "Massospondylus" were described by paleontologist Sir Richard Owen in 1854. Originally, Owen did not recognize these finds as those of a dinosaur; instead he attributed them to "large, extinct, carnivorous reptiles" that were related to today's lizards, chameleons and iguanas. This material, a collection of 56 bones, was found in 1853 by the government surveyor Joseph Millard Orpen in the Upper Elliot Formation at Harrismith, South Africa and was donated to the Hunterian Museum at the Royal College of Surgeons in London. Among the remains were vertebrae from the neck, back, and tail; a shoulder blade; a humerus; a partial pelvis; a femur; a tibia; and bones of the hands and feet. All these bones were found disarticulated, making it difficult to determine if all material belongs to a single species or not. However, Owen was able to distinguish three different types of caudal vertebrae, which he attributed to three different genera: "Pachyspondylus", "Leptospondylus" and "Massospondylus". "Massospondylus" was separated from the other two genera on the basis of its much longer caudal vertebrae, which also led to the scientific name that has been derived from the Greek terms "masson"/μάσσων 'longer' and "sphondylos"/σφόνδυλος 'vertebra'. However, later it was shown that the putative caudal vertebrae of "Massospondylus" were actually cervical vertebrae and that all the material probably belongs only to a single species. On May 10, 1941, the Hunterian Museum was demolished by a German bomb, destroying all the fossils; only casts remain.