 the cretaceous (, ), derived from the latin "creta" (chalk), usually abbreviated k for its german translation kreide (chalk), is a geologic period and system from circa  to  years (ma) ago. in the geologic timescale, the cretaceous follows the jurassic period and is followed by the paleogene period of the cenozoic era. it is the last period of the mesozoic era, and, spanning 79 million years, the longest period of the phanerozoic eon. the cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels and creating numerous shallow inland seas. these oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. at the same time, new groups of mammals and birds, as well as flowering plants, appeared. the cretaceous ended with a large mass extinction, the cretaceousâpaleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles, died out. the end of the cretaceous is defined by the kâpg boundary, a geologic signature associated with the mass extinction which lies between the mesozoic and cenozoic eras. ==geology==  ===research history=== the cretaceous as a separate period was first defined by belgian geologist jean d'omalius d'halloy in 1822, using strata in the paris basin and named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths), found in the upper cretaceous of western europe. the name cretaceous was derived from latin creta, meaning chalk. ===stratigraphic subdivisions=== the cretaceous is divided into early and late cretaceous epochs or lower and upper cretaceous series. in older literature the cretaceous is sometimes divided into three series: neocomian (lower/early), gallic (middle) and senonian (upper/late). a subdivision in eleven [[stage (stratigra
Cretaceous Mesozoic