[4] The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions.

[4] Due to plate tectonics, the Americas were gradually moving westward, causing the Atlantic Ocean to expand.

[4] In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America.

[4] In the Late Cretaceous, the hadrosaurs, ankylosaurs, and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia).

In the southern hemisphere there was instead a more complex fauna of dryolestoids, gondwanatheres and other multituberculates and basal eutherians; monotremes were presumably present, as was the last of the haramiyidans, Avashishta.

Mammals, though generally small, ranged into a variety of ecological niches, from carnivores (Deltatheroida), to mollusc-eater (Stagodontidae), to herbivores (multituberculates, Schowalteria, Zhelestidae and Mesungulatidae) to highly atypical cursorial forms (Zalambdalestidae, Brandoniidae).

These predators fed on the numerous teleost fishes, which in turn evolved into new advanced and modern forms (Neoteleostei).

In temperate regions, familiar plants like magnolias, sassafras, roses, redwoods, and willows could be found in abundance.

[17] Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater, in combination with increased volcanic activity, such as that recorded in the Deccan Traps, both of which have been firmly dated to the time of the extinction event.

In theory, these events reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology.