Around 55 million years ago, Earth's climate underwent a short but intense bout of global warming, accompanied by dramatic shifts in plant and animal life. Of particular interest to paleontologists is the sudden appearance in the Northern Hemisphere of several groups of mammals, including the primates. Researchers have long wondered exactly where these creatures, which differed considerably from the animals they replaced, came from. A recent study indicates that at least one key group, and probably others, originated in Asia. Working with samples obtained from southern China's Hengyang Basin, an international team of scientists led by Gabriel J Bowen of the University of California, USA, employed a variety of techniques to constrain the ages of important Asian animal groups. Comparisons of these sequences with those from North America and Europe clearly showed that a group of dog like carnivores known as hyaenodontid creodonts appeared in Asia before showing up in Europe or North America. And members of the primate and hoofed mammal groups, the investigators found, emerged in Asia no later than they did in North America.