Upper Cretaceous

The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series. The Cretaceous is named after the white limestone known as chalk which occurs widely in northern France and is seen in the white cliffs of south-eastern England, and which dates from this time.

During the Late Cretaceous, the climate was warmer than present, although throughout the period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions.

Due to plate tectonics, the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia. India maintained a northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species.

This was a period of great success for dinosaurs, with many new types appearing and diversifying. The hadrosaurs, ankylosaurs, and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated the large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than the North American varieties.Pachycephalosaurs were also present in both North America and Asia.Dromaeosaurs shared the same geographical distribution, and are well documented in both Mongolia and Western North America. By contrast therizinosaurs (known previously as segnosaurs) appear to have been living solely in Asia.Gondwana held a very different dinosaurian fauna, with most predators being abelisaurs and carcharodontosaurs; and titanosaurs being among the dominant herbivores. Spinosaurids were also present during this time. Velociraptors also began in this time.

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