Turned out that global warming wasn't all bad - 10,000 years ago, somewhere between 1,500 and 4,500 metric tonnes of carbon was released into the atmosphere over the course of several thousand years causing the Earth's temperature to rise and lush forests to spring across the continents and mammals flourished, and "hopped" to the Americas from Asia:
As this picture suggests, it now appears that primates (or at least primates like Teilhardina) originated in Asia and moved to Europe. They then moved from Europe into Greenland and then into North America. The paleontologists suggest that a number of mammals may have taken the same path to North America (rather than going over the Bering Land bridge, as has been suggested in the past). Ocean levels dropped around 55 million years ago, and so the primates and other mammals may have been able to move over land bridges between the continents. Teilhardina's particular way of life also implies that this journey had to have passed through a continuous belt of lush forests. Greenland would have had to have been very green indeed for primates to pass through it. The warm, humid climate would have suited such forests well. It just so happens that paleobotanists have been looking at what happened to plants 55 million years ago, and they've documented a swift spread of tropical trees northwards through North America over 10,000 years. So it appears that global warming laid down the path for the primates, and they raced along it.
Carl Zimmer summarizes a recent PNAS paper in his neat science blog: Link