About 55 million years ago Greenland's eruption and the beginning of the formation of the Atlantic Ocean caused climate warming:
http://www.livescience.com/forcesofnature/070426_petm_volcano.htmlThe article compares atmospheric change at the time to what is happening today.
"During the Paleocene-Eocene Thermal Maximum (PETM), massive amounts of greenhouse gases were injected into the oceans and atmosphere, causing global sea surface temperatures to rise by up to 10 degrees Fahrenheit.
"The event changed global rainfall patterns, broiled and acidified the oceans, and killed up to 50 percent of the world’s deep-sea organisms. The warm climate also opened up new migration routes for horses and other mammals into North America and might have even fueled early primate evolution."
Primates had already evolved but the event presumably separated Old World from New World monkeys.
