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The Cenozoic or Cainozoic Era (sometimes Caenozoic Era) is the most recent of the four classic geological eras. It covers the 64 million years since the extinction event at the end of the Cretaceous that marked the demise of the last dinosaurs and the end of the Mesozoic Era.
Several different subdivisions have been applied to the Cenozoic. The most commonly encountered recognizes seven epochs -- Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. Less common is a division into two Periods Tertiary and Quaternary. The Tertiary is sometimes divided into the Neogene and Paleogene.
The Cenozoic is the age of mammals. During the Cenozoic, mammals diverged from a few small, simple, generalized forms into a diverse collection of terrestrial, marine, and flying animals. Flowering plants and birds also evolved substantially in the Cenozoic.
Geologically, the Cenozoic is the era when continents moved into their current positions. Australia-New Guinea split from Gondwana to drift north and, eventually, abut South-east Asia; Antarctica moved into its current position over the South Pole; the Atlantic Ocean widened and, late in the Era, South America became attached to North America
References and further reading
British Caenozoic Fossils, 1975, The Natural History Museum, London.