Narrator: This is Science Today. Recent discoveries confirm that 65 million years ago, a huge meteor slammed into the earth. But it didn’t kill off the dinosaurs, says paleontologist William Clemens of the University of California, Berkeley. Instead, Clemens points to a changing climate, lots of volcanoes -- and the fact that being big always puts a species at risk.

Clemens: You can see the problem today in trying to maintain populations of elephants or rhinos in Africa. Big animals need lots of room and they need a minimum population size to get together and reproduce, so changes in the topography, the climate, cutting down ranges or breaking them up -- that could be a problem.

Narrator: And whatever killed the dinosaurs, birds and amphibians survived just fine.

Clemens: Yes, you may well have had an impact, it may have had catastrophic effects locally, but to paraphrase a writer in the New York Times who described this discovery as a record of a catastrophic blowtorch of death and destruction -- no, no, that’s way too extreme.

Narrator: For Science Today, I’m Larissa Branin.