Are you in North America? Statistically speaking, yes. Do you like monkeys? Of course you do. Have you noticed that you live in an extremely monkey-poor region of the Earth? Well, here’s what ruined your chance to have monkeys hanging around in your hometown. Yes, I’m bitter too.
About 50 million years ago, North America was full of monkeys. Sure, they were tarsier-like monkeys, which means they were the creepy, small, huge-eyed kind of monkey that always looks strung-out, but still, they were monkeys. They proliferated up and down both North and South America, changing and adapting for 11 million years. Then, around 39 million years ago, the planet took an ice bath. Temperatures dropped, most North American monkeys died out, and what was left were the platyrrhines—the serviceable but unadaptable monkeys that keep to the trees in the hotter parts of South America. Since that time, there’s never been a suitable hot, continuous band of trees to allow them to expand from South to North America.
What cooled the Earth and killed the monkeys? You’re looking at it. The Drake Passage is the bit of water between Antarctica and South America. Before it became a notoriously dangerous and stormy stretch of ocean, it was a barrier. While scientists don’t now for sure that the elimination of that barrier cooled the world, analysis done on the neodymium in fish fossils showed that minerals from the Pacific started flowing into the Atlantic about 40 million years ago. When the barrier got out of the way, warm Pacific water flowed into the cool south Atlantic water, chilled, and sank.
Before the cool down, even Antarctica was a decent place to live; ice core samples show pollen and other biological matter. After the world chilled, it became and stayed an icy wasteland, and all of North America became, from the perspective of the monkeys, just as inhospitable as Antarctica. As for the platyrrhines, or New World Monkeys, they could have gotten to South America anywhere from 39 to 33 million years ago, but whenever they came, they haven’t left. They need trees and they need heat, and the passage between their continent and North America is, sometimes, devoid of either one. Only one fossil shows how tantalizingly close we came. Researchers working in the Caribbean found a fossil of a platyrrhine monkey that had given up its arboreal ways and seemed adapted to for terrestrial life. If it had survived and if it had made the jump to either American continent, it could have charged up through Mexico and populated the Southwest by now.