They found that the birds, rather than forming aversions to taste, developed aversions to the visual features of whatever made them sick. Still, they knew what they shouldn't eat in order to survive. In a previous study in which 10 crocodilians were fed different types of meat, some slightly toxic, Gallup discovered that like dinosaurs, crocodilians did not develop learned taste aversions.

The scientists concluded that though the asteroid played a role in the extinction of dinosaurs, the "plants had already placed severe strain on the species," Gallup said.

"The prevailing view of dinosaur extinction based on the asteroid impact implies that the disappearance of dinosaurs should have been sudden and the effects should have been widespread, but the evidence clearly shows just the opposite: Dinosaurs began to disappear long before the asteroid impact and continued to gradually disappear for millions of years afterward."