T
his chapter examines the life-forms and landforms of the Cretaceous
period and the extinction of the dinosaurs.The Cretaceous, from 135
to 65 million years ago, was named for the Latin word creta,meaning
“chalk”due to vast deposits of carbonate rock laid down worldwide.It was
the warmest period of the Phanerozoic as evidenced by extensive coral reefs,
which built massive limestone deposits (Fig. 159). Coral and other tropical
biota, for which bright sunlight and warm seas are essential, ranged far into
high latitudes.The reefs fringed the continents and covered the tops of extinct
marine volcanoes.
The warm climate was particularly advantageous to the ammonites,
which grew to tremendous size. They became the predominant creatures of
the Cretaceous seas. The dinosaurs did exceptionally well during the Creta-
ceous. However, along with the ammonites and many other species, they mys-
teriously vanished at the end of the period. The extinction was apparently
caused by some sort of cataclysm that created intolerable living conditions for
most species on Earth.
CRETACEOUS CORALS
THE AGE OF TROPICAL BIOTA