The Upper Cretaceous is the last geological epoch in the Cretaceous. It began 100.5 million years ago, and ended 66 million years ago.

The Cretaceous is traditionally divided into Lower Cretaceous (early), and Upper Cretaceous (late), because of the different rocks. The rocks reflect the conditions in which they were formed. From lowest to highest, it is subdivided into the Cenomanian, Turonian, Coniacian, Santonian, Campanian, and Maastrichtian ages.   

The Upper Cretaceous is the time of chalk. Chalk is composed of countless millions of calcareous (CaCO3) plates called coccoliths. They are so small they can only just be seen with a light microscope; details require an electron microscope. The plates are formed by single-celled planktonic algae called coccolithophores, and were laid down in the off-shore seas. 

The only other rock found in chalk is the flint, which is siliceous (silica, SiO2). This derives from those algae and animals which have skeletons of silica. Undoubtedly, this marks periods when the climate was somewhat different.

The Cretaceous was the last period when dinosaurs were the dominant land animals. Triceratops, Tyrannosaurus and Velociraptor lived at this time. The huge Mosasaurus was the dominant marine predator. In the Cretaceous period, birds became more diverse. Flowering plants developed more, and became the dominant plants on land. The Upper Cretaceous ended with the K/T extinction event.

Extinction events 
The end of the Cretaceous period is marked by the huge extinction event which marked the end of the dinosaurs. However, many groups had already disappeared long before then. There was an earlier extinction event in the Upper Cretaceous at the CenomanianTuronian boundary, about 95 to 90 million years ago. All we know about it is that there was huge volcanic activity which led to changes in sea life.

The event brought about the extinction of the pliosaurs, and most ichthyosaurs, and most lines of pterosaurs. Although the cause is uncertain, the result starved the Earth's oceans of oxygen for nearly half a million years. This caused the extinction of about 27 percent of marine invertebrates, including certain planktonic and benthic foraminifera, mollusks, bivalves, dinoflagellates and calcareous nannofossils. This global environmental disturbance increased atmospheric and oceanic temperatures. Boundary sediments show an enrichment of trace elements, and elevated δ13C values. Higher carbon-13 shows a time of lesser biological productivity. This means the seas were no longer so favourable for life at that time, and many species went extinct.

List

Late Cretaceous

Ocean-wide 

 Elasmosaurus
 Mosasaurus

Asia 

 Wannanosaurus
 Protoceratops 
 Sinoceratops
 Jaxartosaurus
 Parasaurolophus 
 Shantungosaurus
 Tsintaosaurus
 Qianzhousaurus
 Gallimimus
 Velociraptor

North America 

 Deinosuchus 
 Pteranodon 
 Quetzalcoatlus 
 Edmontonia 
 Nodosaurus
 Ankylosaurus
 Dracorex 
 Pachycephalosaurus 
 Stygimoloch
 Einiosaurus
 Nasutoceratops
 Pachyrhinosaurus
 Rubeosaurus 
 Chasmosaurus
 Pentaceratops 
 Torosaurus 
 Triceratops 
 Parksosaurus 
 Corythosaurus
 Lambeosaurus 
 Parasaurolophus 
 Edmontosaurus 
 Hadrosaurus 
 Maiasaura
 Daspletosaurus
 Gorgosaurus
 Nanuqsaurus
 Tyrannosaurus Rex
 Struthiomimus
 Chirostenotes 
 Hesperonychus
 Troodon 
 Hesperornis
 Alexornis
 Alamosaurus
 Alphadon

South America 

 Carnotaurus
 Argentinosaurus
 Giganotosaurus

References 

Cretaceous