CRETACEOUS PERIOD www.johnsibbick.com
The Cretaceous was a period with a relatively warm climate,
resulting in high eustatic sea levels and creating numerous shallow inland
seas. These oceans and seas were populated with now extinct marine reptiles,
ammonites and rudists, while dinosaurs continued to dominate on land. At the
same time, new groups of mammals and birds, as well as flowering plants, appeared.
The Cretaceous ended with a large mass extinction, the Cretaceous–Paleogene
extinction event, in which many groups, including non-avian dinosaurs,
pterosaurs and large marine reptiles, died out. The end of the Cretaceous is
defined by the K–Pg boundary, a geologic signature associated with the mass
extinction which lies between the Mesozoic and Cenozoic Eras.
Flowering plants (angiosperms) spread during this period,
although they did not become predominant until the Campanian stage near the end
of the epoch. Their evolution was aided by the appearance of bees; in fact
angiosperms and insects are a good example of coevolution. The first
representatives of many leafy trees, including figs, planes and magnolias,
appeared in the Cretaceous. At the same time, some earlier Mesozoic gymnosperms
continued to thrive; pehuéns (monkey puzzle trees, Araucaria) and other
conifers being notably plentiful and widespread, some fern orders such as
Gleicheniales appeared as early in the fossil record as the Cretaceous, and
achieved an early broad distribution. Gymnosperm taxa like Bennettitales died
out before the end of the period.
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