[url]http://www.nytimes.com/2007/03/28/science/28cnd-mammal.html?ex=1332734400&en=8f6973daa8292236&ei=5088&partner=rssnyt&emc=rss[/url]

[INDENT][I]The mass extinction that wiped out dinosaurs and other life 65 million years ago apparently did not, contrary to conventional wisdom, immediately clear the way for the rise of today’s mammals.

In fact, the ancestral branches of most mammals, including primates, rodents and hoofed animals, emerged long before the global extinction and survived it more or less intact. But it was not until at least 10 million to 15 million years afterward that the lineages of living mammals began to flourish in number and diversity.

Some mammals did benefit from the extinction, but these were not closely related to extant lineages and most of them soon died off....

The new study confirmed and elaborated on earlier research by molecular biologists indicating that many of today’s mammalian orders originated from 100 million to 85 million years ago. The reasons for this evolutionary burst are not clear....

"The big question now is what took the ancestors of modern mammals so long to diversify," he continued. "Evidently we know very little about the macroecological mechanisms that play out after mass extinctions."[/I][/INDENT]