Or on spaceships.
No, actually it was vegetation rafts.
I kid you not:
Primates came to the New World (meaning North and South America) from, we think, Africa. As improbable as it sounds, scientists think early primates crossed the Atlantic Ocean and landed on the shores of both continents tens of millions of years ago, probably on some kind of vegetation raft…Fossils have been recovered of early primates in Texas a whopping 43 million years ago, the oldest primate fossil ever found in North America. But the continents looked very different then, compared to now; most importantly, North and South America were completely different islands. The Isthmus of Panama, which we now refer to as Central America, didn’t appear until much later, by which time the climate on both Americas was very different from when the primates first landed there.
When they did first land here, the climate was much warmer than it is now, and the primates evolved and diversified to take advantage of that…Then the planet began to cool, and cool quickly. Forests died out. The poles covered with ice. Many of the flora and fauna that had populated the planet during the Eocene just couldn’t survive in the new, colder world. This event is called the Grande Coupure–occurring about 33.9 million years ago, it was a mass extinction of animals, in which most of the world’s creatures (aside from a precious few, like the Virginia opossum and the dormouse) were unable to adapt to the new climate and perished. It hit the primate family especially hard. In the New World, the primate population shrunk significantly. Any primate living in, say, the Great Lakes region simply went extinct, unable to cope with the new Wisconsin winters.
In South America, the primates contracted to the region around the equator.
Those New World monkey survivors all occupy a particular niche: they are arboreal tropical-forest dwellers. Some of them journeyed back up to Central America later, when the isthmus connected the continents, but were stopped by the deserts in Mexico.
I keep trying to picture those monkeys on those rafts, though. What did they eat? How did they survive? It seems so improbable. And yet I found a Wiki entry dealing with the general phenomenon, entitled “oceanic dispersal.” These “rafts” are not the Huckleberry Finn variety—they are big.
Here’s an article on how rafting works, although it doesn’t go into the monkey story. But it describes a large raft (20-meter by 6-meter by 2-meter) that came to Oregon from Japan after the 2011 earthquake tsunami, which had to be dealt with because it constituted a threat to the Oregon coastal ecosystem.
There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.
[Hat tip: Ace's.]