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.
Ceratosaurus
The first specimen, the holotype USNM 4735, was discovered and excavated by farmer Marshall Parker Felch in 1883 and 1884. Found in articulation, with the bones still connected to each other, it was nearly complete, including the skull. Significant missing parts include an unknown number of vertebrae; all but the last ribs of the trunk; the humeri (upper arm bones); the distal finger bones of both hands; most of the right fore limb; most of the left hind limb; and most of the feet. The specimen was found encased in hard sandstone; the skull and spine had been heavily distorted during fossilization. The site of discovery, located in the Garden Park area north of Cañon City, Colorado, and known as the Felch Quarry 1, is regarded as one of the richest fossil sites of the Morrison Formation. Numerous dinosaur fossils had been recovered from this quarry even before the discovery of "Ceratosaurus", most notably a nearly complete specimen of "Allosaurus" (USNM 4734) in 1883 and 1884.