"In the new research, U-M paleontologist Philip Gingerich and coworkers re-evaluated the four hypotheses by comparing with unprecedented precision the times of first appearance of Teilhardina in Asia, Europe, and North America. To achieve such precision, they used a carbon isotope curve recently documented on all three continents. Carbon in the atmosphere, earth and living organisms differs in the proportion of carbon-12 and carbon-13 present. A flood of carbon-12 is associated with the onset of an event known as the Paleocene-Eocene thermal maximum (PETM), one of the most rapid and extreme global warming events recorded in geologic history. It was during the PETM that modern primates first appeared 55 million years ago. Teilhardina in Asia precedes the maximum flood of carbon-12, Teilhardina in Europe coincides with it, and Teilhardina in North America appears just after the maximum. Based on this evidence, the researchers concluded that none of previously proposed scenarios was likely. Instead, they propose that Teilhardina migrated from South Asia to Europe, crossing the Turgai Straits---an ancient seaway between Europe and Asia---and then spread to North America by way of Greenland.

The whole dispersal event happened within about 25,000 years."
http://www.eurekalert.org/pub_releases/2006-07/uom-agw072506.php
[linked from http://www.junkscience.com/]