Dinosaurs were doing fine until a huge space rock struck Earth 66 million years ago, and except for a stroke of bad timing, they might still be around. So concludes a paper published online today in Biological Reviews. Studying the latest evidence for the date of the so-called K-Pg extinction and the diversity of life for millions of years before and after it occurred, the authors found that dinosaurs were not already on the way out when the impactor hit, and that other explanations offered for their demise—such as volcanic eruptions—probably don’t hold water. But a temporary drop in the numbers of large herbivores may have left the dino ecosystem vulnerable to catastrophic extinction at just the wrong moment, National Geographic reports. So the big guys perished, and only birds made it through.