CretaceousEarly

The Early Cretaceous, sometimes referred to as the Cretaceous Early, is the first subdivision of the Cretaceous Period. It spans roughly 145 to 100.5 million years ago, from the base of the Cretaceous to the boundary with the Late Cretaceous. The division includes the ages Berriasian, Valanginian, Hauterivian, Barremian, Aptian, and Albian.

Geology and climate during the Early Cretaceous were characterized by warm conditions and high sea levels. Global climates remained tropical to subtropical with limited polar ice, contributing to extensive shallow inland seas that flooded parts of multiple landmasses. Plate tectonics continued to rift continents apart, contributing to rising ocean basins and the gradual opening of new sea routes. The distribution of land and sea created diverse marine and terrestrial environments that favored rapid faunal and floral changes.

Biologically, the Early Cretaceous saw important evolutionary developments. Gymnosperms remained common, but the earliest angiosperms (flowering plants) appeared during this interval, beginning a major shift in terrestrial ecosystems. Invertebrate and vertebrate groups diversified, including the early diversification of flying vertebrates and the continued dominance of various groups of dinosaurs in many regions. Notable fossil assemblages from this time include the Jehol Biota of northeastern Asia, which documents early birds and a diverse ecosystem for plants and animals.

The Early Cretaceous laid the groundwork for the later Cretaceous evolutionary radiations, including more widespread angiosperm diversification and further changes in dinosaur and marine faunas.