Cretaceous

The Cretaceous period saw the last and most diverse group of dinosaurs, including famous species like Tyrannosaurus rex, Triceratops, Velociraptor, and the massive Argentinosaurus. The ecosystems during this time were highly complex, with large herbivores, apex predators, and a variety of smaller theropods and ornithopods coexisting in different environments.

One of the major evolutionary developments during the Cretaceous was the appearance and spread of flowering plants, or angiosperms. These plants rapidly diversified and became dominant in many ecosystems, outcompeting gymnosperms and ferns. The emergence of flowering plants also led to the co-evolution of insects, such as bees and butterflies, which played key roles in pollination.

Geologically, the breakup of the supercontinents continued during the Cretaceous. Laurasia and Gondwana further fragmented into the continents we recognize today, and the Atlantic Ocean widened as the continents drifted apart. Tectonic activity also contributed to the formation of new mountain ranges and volcanic activity, particularly in what is now the western United States and South America.

The Cretaceous climate was warm and humid, with high sea levels creating extensive shallow inland seas. These seas fostered diverse marine ecosystems, including the proliferation of ammonites, mosasaurs, and marine reptiles. However, the warm and relatively stable climate came to an abrupt end with the Cretaceous-Paleogene extinction event, around 66 million years ago.

The leading theory for the K-Pg extinction is the impact of a large asteroid, approximately 10 kilometers in diameter, which struck the Yucatán Peninsula, creating the Chicxulub crater. This impact caused widespread wildfires, tsunamis, and a “nuclear winter” effect that drastically reduced global temperatures. The resulting environmental changes led to the extinction of approximately 75% of all species, including the non-avian dinosaurs, paving the way for mammals to dominate the Cenozoic era.