The Miocene is the first epoch of the Neogene period and the fourth of the Cainozoic. It started about 23 million years ago and ended about 5.33 million years ago. The rock beds that mark the start and end are well known, but the exact dates of the start and end of the period are uncertain. The biota becomes 'modern'.
The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words μείων (meiōn, “less”) and καινός (kainos, “new”) and means "less recent", because it has 18% fewer modern sea invertebrates than the Pliocene.
As the earth cooled, it went from the Oligocene epoch, through the Miocene, and into the Pliocene. The Miocene boundaries are not set at any particular world wide event. They are set at regional boundaries between the warmer Oligocene and the cooler Pliocene epochs.
The plants and animals of the Miocene were fairly modern, but familiar present-day species had not yet evolve. Modern families of mammals and birds existed. Whales, seals, and kelp spread. Modern sharks appeared, including the huge Megalodon. Grasslands became more common. Mammalian browsers became less common, and grazer species became more common. About 100 species of ape lived at that time, and cetaceans were very common in the seas. The giganic shark Carcharodon megalodon may have preyed on them.
The climate was warm in the Miocene, especially in the first half. The diagram shows that throughout the Oligocene and the first half of the Miocene, climate remained warm.
This meant that Africa (and elsewhere) was much more forested than today, and that the herbivorous mammals were mainly browsers rather than grazers. In the second half of the Miocene temperatures dropped, and grasslands began to expand.
Another great event, which undoubtedly affected climate, was the refilling of the Mediterranean basin. The so-called Zanclean flood is thought to have refilled the Mediterranean Sea 5.33 million years ago. This reconnected the Mediterranean Sea to the Atlantic Ocean. It is possible that even before the flood there were partial connections to the Atlantic Ocean.
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